KR20040093740A - A miniaturized contact spring - Google Patents

Abstract

The present invention provides a method for increasing the yield strength and fatigue strength of miniature contact springs 507 that can be made into an array with a very small pitch. The present invention also provides a method of minimizing adhesion of the contact pad material to the tip of the spring when repeating contact without affecting the reliability of the small spring 507. In addition, the present invention provides a method for manufacturing a spring 507 that allows a relatively high current flow without significantly degrading its lifetime.

Description

Interconnect device and miniature spring manufacturing method {A MINIATURIZED CONTACT SPRING}

Small springs can also be manufactured with pitches of less than 10 μm, since such small spring arrays can also be manufactured at pitches less than 10 μm, such as integrated circuits, PCBs, interposers, for purposes such as testing, burn-in, and packaging. It has been widely used as electrical contacts for space transformers and contact pads or I / O terminals on probe chips. Miniaturized stress metal film springs, typically patterned by photolithography, include a fixed portion, also called an anchor portion, attached to the substrate, and a free portion initially attached to the substrate. A lifted portion, also referred to as a free portion, is away from the substrate forming a three-dimensional structure due to the inherent stress gradient in the spring upon release. Typically, the stress gradient in the film is created through sequential deposition of a plurality of thin film layers by sputtering or electroplating under different process conditions. A typical stress metal film spring is shown schematically in FIG. 1A, which has an annotating portion 101 and a spring tip 105 associated with a terminal 102 or electrical connection attached to a substrate or electrical element 103. A free portion 104. Examples of such structures are disclosed in US Pat. No. 5,613,861 (Smith) and PCT / US00 / 21012 (Chong, Mok).

Other types of springs include discrete springs that are fabricated individually or in groups and mounted on a substrate, such as those used in wafer test or hot test assemblies or including integrated solid devices, such as semiconductor devices. Another type of such spring is a cantilever fabricated together on a substrate using photolithography, as disclosed in patent documents such as PCT 01/48818, PCT WO97 / 44676, US Pat. No. 6,184,053, and PCT WO01 / 09952. cantilever) spring. Some of these springs are fabricated individually or in groups on a sacrificial substrate and then mounted on a substrate comprising a semiconductor device or a substrate used in a wafer test or hot inspection assembly. FIG. 1B is a schematic cross-sectional view of a typical photolithographic patterned freestanding cantilever spring fabricated on a sacrificial layer, with a base region at one end attached to an electrical contact pad 202 of a substrate 203. 201, a contact tip region 204 at the other end of the spring, and a main body 205 at the center of the spring connecting the base region 201 and the contact tip region 204. The problem with this type of spring is that these springs are too long. Shorter and smaller springs are preferred for testing and high temperature inspection of some current and next generation integrated circuits, including contact terminal pads having very small pitches of, for example, 20-50 μm.

A method for producing shorter springs using a photolithographic process to add thicker metal coatings is defined in this patent document. One method is disclosed in WO 01/48870. This method uses electroplated photoresist to allow the metal to be plated on top of the freestanding spring. However, at the dimensions required for probe ICs with a pad pitch of less than 150 μm, the freestanding spring is insufficient to maintain the backside photoresist without significantly reducing the height of the probe required for compliance. Has strength. Any non-uniformity in the photo process also causes the spring height to be non-uniform so that it cannot meet the uniformity requirements needed to remain on the IC pad during testing.

The method disclosed in patent application (WO 01/48870) also has additional problems in controlling the lift height after plating. One of the purposes of having a freestanding spring is to provide a configuration or structure that supports thicker plated metal. If only one side of the spring is plated, the spring is bent by the stress in the plated film so that the lift height is different. If the film is stretchable, the film is bent upwards, and if the film is compressive, the film is downwards. All of these stress conditions are difficult to control for the spring lift uniformity and tolerance required to test the IC. In addition, the compressive spring is stronger than the tension spring, and the spring with the compressive plating film has a lower lift height to the point that it is not flexible enough to be a useful probe. There is also a limit to the height at which the freestanding spring can be lifted prior to plating to compensate for this compression effect. The probe needs to contact the IC electrical pads at an angle of less than 90 degrees. Increasing the lift height allows the spring to rotate around it and draw a 360 degree circle to the substrate. As a result, the process disclosed in this patent application does not meet the requirements for controlling the uniformity of the lift height of the spring array required for IC testing.

One method of forming a probe in patent application WO 01/48870 is to assemble a tip on a plated spring and a spring fabricated on a sacrificial substrate to a second interconnect substrate. This assembly process adds placement errors, resulting in a higher manufacturing cost than fully integrated connection buttons as described herein.

Another method disclosed in U.S. Patent No. 6,528,350 separates the photoresist coating, i.e. the mask from the spring, and allows the plating of the freestanding portion of the spring using a release layer island. If the release mask is stopped adjacent to the base (anchor) of the spring and does not extend along the base of the spring, the thickness and width of the free portion of the spring adjacent to the base become much larger than the base area at the time of plating. As a result, the freestanding portion of the spring is mechanically weaker near the base area. Since the bending moment is the best in this area, when the spring tip is applied during the IC test, the spring ruptures early and thus cannot meet the life requirement of the probe required for the IC manufacturing line. In other methods described in US Pat. No. 6,528,350 in which the photoresist mask does not cover the freestanding portion and the ankle portion of the spring during plating, there are still discontinuities within the width that tend to break. Alignment of the mask and control of the spring release process also cause serious problems, resulting in uneven plating and variations in lift uniformity. Another important issue in this process arises from the high resistance of the relatively thin release layer and the stress metal film through which the plating current flows. The current density varies widely with the distance from the power connection point at the edge of the substrate. As a result, the properties of the plated film, such as microstructure, thickness, stress, etc., vary widely in different regions of the spring. As a result, this process does not produce an array of springs with fairly uniform and controlled properties, such as lift height, which is essential for effective IC testing.

The present invention includes a number of means for avoiding the problems associated with the above two methods, and provides a solution to fabricate an array of springs suitable to meet the stringent requirements of IC testing at the wafer level. In particular, the present invention makes it possible to produce arrays of springs with fairly uniform lift heights and properties and durability. For example, the present invention discloses an example of enclosing an entire spring core, i.e. both the freestanding and the anchored portions, with an electrodeposited film having a stable stress capable of maintaining a spring height with proper uniformity after electrodeposition. Doing. In another example, a method of selectively plating a spring without using any photoresist mask is disclosed.

Miniature contact springs undergo a number of contact operations during testing that apply various levels of stress to the spring, including cyclic stress. In addition, in packages that use contact springs to couple two elements, such as chips and chip carriers, the springs are stressed during testing and operation. The spring must be able to withstand this stress without failure. However, small springs of about 400 μm × 60 μm × 20 μm size have been observed to fail, i.e., plastically deform, after 10,000 touchdowns of contact force typically exceeding about 1 gf. The main cause of failure is that the alternating stress exceeds the fatigue strength of the spring material. Fatigue strength refers to the alternating stress level at which a material can withstand a certain number of cycles. This is usually part of the yield strength of the material and corresponds to signs of plastic deformation, ie instantaneous permanent deformation. Experimental observations have shown that a spring against failure is required to improve the performance and quality of the spring, since a force in excess of about 1 gf is generally required to form good reproducible contacts on aluminum with low contact resistance. Should increase considerably. Springs with larger cross sections can withstand similar or greater forces without failure because the resulting stress is lower, but they limit the spring's pitch.

In certain operations, such as high temperature inspection of the device, the contact spring is required to contact the device terminal, for example at a high temperature of about 100 ° C. Such contacts may also be required to allow relatively high currents to flow, for example 250 to 500 mA, during this operation. Under this condition, the contact resistance should be considerably low, for example 0.1 milliohms, so that the tip region of the contact of the spring may be damaged by overheating. One way to achieve low contact resistance is to increase the contact force by increasing the thickness of the spring. However, a higher contact force increases the stress generated in the body of the spring, especially near the base region, thus increasing the probability that the spring will fail early during repeated touchdowns.

In addition, the material from the electrical contact pads or terminals tends to stick to the tip of the spring while repeating contact. If the pad material sticks to the tip of the spring to increase the contact resistance, or to form a compound that sticks on the exposed portion of the pad material, the electrical contact drops after repeated touchdown. This also shortens the life of the spring. Therefore, the tip structure of the contact portion is preferably made of a material that is not strongly adhered to the contact pad or the terminal.

Therefore, a mechanism is needed to maximize the yield strength and fatigue strength of the small springs within the compact requirements.

There is also a need for a mechanism to minimize adhesion of the contact pad material to the tip of the spring without substantially affecting the reliability and electrical conductivity of the spring when repeating contact.

There is a need for a method of making a spring that is highly resistant to compliant stresses that provides a uniform spring height and provides a sturdy tip structure.

The present invention relates generally to highly miniaturized springs. More specifically, the present invention relates to compact contact springs and methods of increasing the yield strength and fatigue strength of these springs.

1A is a schematic diagram illustrating an exemplary stress metal film spring according to the prior art.

1B is a schematic diagram illustrating a typical cantilever spring according to the prior art.

2 shows a stress-strain curve of a thin film zone corresponding bulk material.

3A and 3B are schematic views showing a stress metal film spring having a multilayer structure according to the present invention.

4 is a schematic diagram illustrating a stress metal film having a multilayer structure including at least one high thermal conductivity film, in accordance with an embodiment of the present invention.

5 is a schematic diagram illustrating a solution for spring design and fabrication in which metal filled vias, insulating polymer film, and electrical traces are used, in accordance with an embodiment of the present invention.

6 is a schematic view of a stress metal film spring formed on a via providing electrical connections to the backside of a substrate, in accordance with the present invention.

7 is a schematic view of a stressed metal film spring plated to improve toughness, in accordance with the present invention.

8 is a schematic representation of a plated stress metal film spring coated with a photoresist, in accordance with the present invention.

9 is a schematic representation of a plated stress metal spring coated by a photoresist patterned to expose the tip of the spring, in accordance with the present invention.

10 is a schematic representation of a plated stress metal spring having tip material of a plated contact on an exposed portion of a tip in accordance with the present invention.

11 is a schematic representation of a plated stress metal spring having a tip material of a contact after photoresist removal, in accordance with the present invention.

12A is a schematic diagram of a stress metal film spring having a tapered variable width, in accordance with an embodiment of the present invention.

12B is a schematic diagram illustrating a tapered stress metal film spring in which a tip region is coated with a contact material, in accordance with an embodiment of the present invention.

13 is a schematic representation of a stress metal spring plated with tip material of contacts in an insertable array, in accordance with the present invention.

14A and 14B are schematic views showing two cross-sections of a typical freestanding non-stress metal cantilever spring in accordance with one embodiment of the present invention.

The present invention provides a method for increasing the yield strength and fatigue strength of small contact springs that can be made into arrays with very small pitches. The present invention also provides a method of minimizing adhesion of the contact pad material to the tip of the spring when repeating contact without affecting the reliability of the small spring. In addition, the present invention provides a method for manufacturing a spring that allows a relatively high current flow without significantly degrading its lifetime. The present invention also provides a method for manufacturing a robust spring for coupling a die-bonding terminal to a corresponding input-output pad of a substrate comprising an inorganic or organic material for the manufacture of a reliable package. The bond can be prepared, for example, using a solder or conductive adhesive comprising an conductive adhesive film anisotropically.

The stress metal spring according to the present invention comprises a multilayer film structure. The thin film has a substantially higher yield strength and fatigue strength than the corresponding bulk material, so these springs can repeat the touchdown during testing or hot inspection without any large plastic deformation.

Deposition of compressively stressed films onto core films has been found to be useful for increasing the life of springs. This makes it possible to produce stress metal springs that can exert great forces on the electrical contact pads or terminals.

The thin film is deposited so as to have a gradient change in composition, either continuously or in minute discontinuous steps across the interface between two different materials, so the modulus of elasticity generally increases gradually from the spring surface towards the spring core. The resulting spring appears to greatly increase its life during repeated touchdowns.

Suitable materials and / or processes have been found to be useful for increasing the robustness of interfaces in multilayer structures. It is preferred that materials of similar lattice parameters are used for adjacent films, and that amorphous or nano-crystalline films are used as the interface. The interface can be formed by "phasing-in" the material of two adjacent layers or by using an alloy of the materials of two adjacent layers.

The thickness of the free portion of the thin film is preferably in the range of 4 to 35 μm, which allows for a reliable and low electrical contact resistance between the spring tip and the contact pad or electrical terminals made of different materials.

At least one highly thermally conductive film in a multilayer film structure is preferably used in dissipating heat during testing or high temperature inspection at relatively high currents.

Changing process parameters during deposition of the film forming the spring structure has been found to be useful for improving the quality and reliability of the spring. For example, thin films, including coatings of spring cores, are deposited with suitable microstructured features such as, for example, very small particle sizes less than 200 nm, in order to increase both the yield strength and the fatigue strength of the spring.

The force used to make good electrical contact between the spring and the contact pad is substantially reduced. The suitable range of contact force for aluminum (Al) is 0.8 to 10.0 gf. For contact pads made of gold, copper or solder, the force for good electrical contact is much smaller. The low force of the photolithographically patterned small contact springs includes a probe chip assembly comprising a probe chip, i.e., a substrate having an IC terminal, an interposer and an attachment probe spring in contact with the assembly fixture for testing and high temperature inspection and packaging. To facilitate the configuration of the. The assembly is greatly simplified by the use of these low force springs since bending, warping and alignment problems are minimized.

Methods for improving the life of the spring include methods for minimizing the surface roughness.

Changes in the dimensions of the spring, such as width and thickness, have also been found to be useful for improving life. In one embodiment, the free portion of the spring is tapered.

The present invention also provides a low cost effective method of electrodepositing the top film onto stress metal springs, circuit traces and electrical contact pads without using any masks.

In one embodiment, the tip region of the spring, called a button spring tip, is selectively coated with a material that minimizes adhesion of the contact pad material during repeated touchdowns, using a lithographic process. The thickness of the spring tip region is formed before the spring is released from the substrate.

In another embodiment, after the spring is lifted and electroplated as required with a material that minimizes adhesion of the contact pad material while repeating the touchdown, a photoresist is applied and patterned to selectively coat the tip region.

The solution to stress metal springs can be applied to other types of cantilevers. One embodiment is applicable to other cantilever springs, with or without a button contact structure in the contact tip region of the spring. Multilayer films are sequentially selected and deposited according to the particular principle of making robust high performance springs with high durability and increased lifetime. This principle requires the film to be selected and deposited sequentially in such a way that the elastic modulus of the outer layer of the spring is lower than the elastic modulus of the inner layer and the elastic modulus gradually increases from the surface layer of the spring to the innermost layer.

In another embodiment, to increase both the yield strength and the burst strength of the spring, a thin film comprising a non-stressed metal cantilever spring is deposited to have a suitable microstructured feature, such as an ultra-small particle size of less than 200 nm.

In yet another embodiment, the non-stress cantilever spring layer consists of at least one deposited film layer with built-in compressive stress.

According to the same principle, shorter springs with stronger and higher strength can be produced.

The present invention is applicable to the testing and high temperature inspection of various types of solid state devices such as silicon and III-V devices, display devices, surface acoustic devices, micro-electromechanical (MEMS) devices.

The invention is also applicable to a package in which the electrical terminals of the electronic device are coupled to corresponding contact pads of adjacent substrates.

Small springs can be manufactured using discrete component manufacturing techniques such as thin films or wire bonding. In general, for springs that work satisfactorily in a wide range of applications, the yield strength of the material should be higher than the stress applied to the spring during testing or hot testing or in the assembled package. Many thin film stress metal springs have been observed to plastically deform during testing because the yield strength of the spring material is lower than the applied stress. Stress metal films typically comprise a strong core film made of a material such as molybdenum (Mo) or its alloys, tungsten (W) or its alloys, and additional tops such as nickel or nickel-cobalt (Ni-Co) alloy films Has a film coating. Some of these films are relatively thick and typically have a thickness of 4 × 10 ³ nm, which is required to increase the force that needs to be applied by a spring to the contact surface for good electrical contact. High yield strength of such films is required to ensure satisfactory spring performance.

Since the stress metal springs produced by the present invention are fabricated on a substrate or electrical device using thin film / IC or MEMS technology, the springs disclosed herein can be used to produce probe cards, interposers, space transducers, PCBs, wafers, and electronics. Testing, high temperature inspection and packaging (three-dimensional packaging and chip to chip-carrier bonding) including devices and microchips with very small contact pads or I / O terminals with a range of 3 to 100 μm It is particularly suitable for applications, including). Most existing technologies are not suitable for these applications. The size of the corresponding spring or spring terminal is very small, 10 to 1,000 mu m in length, 3 to 500 mu m in width and 0.1 to 40 mu m in thickness. The radius of rotation of the lifted core is usually 20 to 2,000 μm. The idea of the present invention can also be used to create springs or spring terminals outside the disclosed size and pitch ranges. The idea of the present invention can also be applied to both stress metal springs and other small springs including thin films.

In one embodiment of the present invention, multiple layers of very thin films having a thickness of less than about 1.5 to 2 μm are used to increase the yield strength of the thin film spring material. This is particularly suitable for forming a coating layer on the thin film spring core. The stress-strain curve of the thin film shown schematically in FIG. 2 is very different from the stress-strain curve of the corresponding bulk material. The material in the thin film exhibits higher yield strength, that is, the film retains elasticity at higher stress than the same material in bulk form, and is relatively plastically deformed before failure. In general, the strength of a thin film is much closer to the theoretical strength of the material than the yield strength of the corresponding bulk material. For example, when the film thickness increases to 2 μm or more, the film exhibits increased bulk stress-strain properties. As a result, the elastic limit of the thicker film is lower than the elastic limit of the thinner film. In addition, the grain size of very thin films is much smaller than that of relatively thick films, thereby increasing both yield strength and fatigue strength. Thus, springs with thinner films are more robust.

In this preferred embodiment, the discontinuities in the atomic arrangement are intentionally introduced at the interface between two adjacent films so that both films have respective mechanical properties and the interface prevents defect propagation from one film to another. Changing the deposition parameters after the film has been deposited to the required thickness is one way to accomplish this. Another way to form this interface is to deposit two different materials sequentially next to one another. This involves using two different materials with similar lattice parameters in two adjacent layers to enhance bonding at the interface, for example Cu and Ni. This approach also works if the lattice parameters of two adjacent layers are not very similar to each other. Using this approach, a plurality of thin film layers can be deposited to make up the desired spring film thickness. The upper layer of the spring is preferably a thin film structure that prevents deterioration of the surrounding environment and sticking of the contact material to the spring surface during storage or operation. This embodiment is schematically illustrated in FIGS. 3A and 3B, where A, B, C, and the like represent different materials. In order to form the next adjacent layer by depositing the same material but using different process parameters, an asterisk indicating the adjacent layer, ie A and A ^* , is used.

Multi-layer springs formed in this way are annealed at relatively low temperatures for a short time, for example at 150 ° C. for 10 minutes, if desired, to mitigate internal stresses in the film to facilitate bonding between adjacent layers and add to the rigidity of the springs. Can be.

In variations of this embodiment, deposition conditions may be varied to produce less than about 200 nm of amorphous or amorphous thin film between two relatively thick film layers of about 2000 nm or less to facilitate bonding between adjacent layers. Examples of such interlayer film materials include Au, Ag, Ni, Cu, and the like.

Various deposition techniques, such as physical vapor deposition (eg sputtering or CVD), electro-deposition, and chemical vapor deposition, can be used to deposit the multilayer film. In certain embodiments of springs suitable for making good electrical contact with contact pads or terminals of various materials, the springs have a stress gradient of about 1-4 μm with a stress gradient over the thickness (from the compressed bottom to the extended one). A sputter deposited core of a thick Mo-Cr film. After the free portion of the spring is loosened using a film deposition technique such as electroplating technique (dc and / or pulse deposition), a multilayer thin film, for example Ni or an alloy thereof covering the core, is deposited on the front side of the core to The spring thickness is about 18-35 μm. Electrodeposition techniques, ie electroplating and electroless plating, are the preferred techniques for coating the core film. Pulsed plating, an electrodeposition method, is particularly useful for coating because it tends to produce higher concentration films. A composition modulated electrodeposition technique may be used to deposit the multilayer film.

Electrical contact pads on different substrates or electrical elements having a very thin (thickness less than about 2 μm) film or a multilayer of relatively thick film, for example thicker than about 2 μm, and a stress metal spring comprising a free layer of 1 to 45 μm It has been found to be suitable for forming good electrical contacts having a variety of materials including electrical terminals. The preferred thickness range in making the free portion of the spring is 4 to 35 μm. The tip at the free end of these springs having an appropriate thickness within this preferred range, and predominantly gold (Au), copper (Cu) or commonly used lead-free or lead-containing solder or aluminum ( Good electrical contact (very low contact resistance) was made between the electrical contact pads or terminals comprising Al).

In another preferred embodiment, the resistance to failure of the spring, which consists of a relatively thin thickness of 0.2 μm or another film having a thick film of 10 to 15 μm, is achieved by electrodeposition, for example, of all or relatively thick top films, in particular springs. By electroplating the film on the core film in such a way that the film close to the surface remains under compressive stress, it is substantially increased. This means that the finished spring is designed to be prestressed in advance. In order to maintain pre-stressed conditions, both the top material and the core material must have a high elastic limit to withstand plastic deformation. In addition, the interface between the different film layers must be strong. In a typical embodiment, the overlying film with compressive stress is made of nickel and has a thickness of about 10 μm on both sides of the Mo—Cr core film. For example, using appropriate deposition conditions, such as additive concentration in an electrodeposition bath, such films can be produced. The spring created in this way can withstand many touchdowns without any failure. One cause of a spring failure is that high spring stresses occur on the surface of the spring when the spring is pressed to contact the electrical contact pads or terminals. The fatigue strength of the material is generally lower under tensile mean stress than under compressive mean stress. The method described above minimizes the occurrence of elongation stress on the spring surface when the spring is pressed in contact with the contact pad or terminal, thus increasing the spring's resistance to failure. This approach and the following disclosure allow for the manufacture and use of thin stress metal film springs having a relatively large overall thickness useful for generating the high contact forces required for electrical contact pads or terminals in some applications.

Note that the complete spring is designed to be compressive. Pre-stressing is preferably achieved by compressive stress. However, the range may be low in compressive stretch stress versus compressive stress, for example, stretch force 30 MPa versus compressive force 70 MPa. The stress depends on the thickness of the Ni plating for the same additive concentration. The thinner the film, the higher the stress. For example, for a 1.5 μm thick film, the stress has a compressive force of about 70 MPa. The range of compressive stresses that can be produced in plated Ni springs having the same additive concentration is about 6-70 MPa (compression) over a thickness range of 25-1.5 μm. Thus, stresses for various Ni film thicknesses can be controlled through changes in additive concentration.

Another effect of changing the concentration of the additive in the plating method is reflected in the grain size of the plated film. For plated springs that currently increase the concentration of the additive, the particle size was found to be one fifth (20%) of the initially plated sample with the smaller additive concentration. Smaller particle sizes increase the yield strength of the thin film (dependency of d ^-1/2 ). This is a major factor in increasing the life of the spring during repeated touchdowns. The preferred range of diameters of particles, such as Ni, in the film covering the spring core is 3 to 500 nm, with the preferred value usually being 50 nm. The plated top film seems to be stronger as the particles become more equiaxed, for example with a ratio of large to small particles of less than two.

In another preferred embodiment, the selection of the film material for the deposition of a multilayer stack of films consisting of relatively thick (less than about 1.5 to 2 μm) films, or thicker than about 1.5 to 2 μm, has a lower modulus of elasticity. The film is deposited near the spring surface and the film with higher modulus of elasticity is deposited on the core side. In a variant of this embodiment, the film is selected and deposited on the core in such a way that the modulus of elasticity from the surface of the spring to the spring core increases substantially continuously, i.e., the composition is deposited to gradient. Gradient changes in modulus and composition from the spring surface to the core, across the interface between two different materials, either continuously or in minute discontinuous steps, are used to disperse stress at critical locations and thus permanent damage To prevent the start of. In these configurations, because the springs are pressed into electrical contact with the contact pads or terminals, the critical elongation stresses that agglomerate damage at the surface are lower at the surface as the stress spreads from the surface into the spring at a higher rate below the surface. This reduces the probability of cracking on the spring surface during repeated touchdowns, thus increasing the life of the spring. As an example of this embodiment, the spring surface layer (ie, the outer surface of the overlayer stack) may be a palladium alloy (containing Ni, Co or Pt), a gold alloy (containing Ni or Co), a Pt alloy, or the like. On the other hand, the film layer closer to the spring core, for example Mo-Cr, is made of nickel or a Ni alloy, for example Ni-Co. The higher the concentration of Pd or Au in nickel, the smaller the modulus of elasticity. Thus, in another example, the life of the spring is increased by depositing nickel or alloys thereof. Thus, in another example, the life of a spring by depositing a nickel or alloy thereof with a higher modulus of elasticity on a core film such as Mo-Cr and subsequently depositing a layer of increased Pd amount on the top film containing Ni. This increases. In this case the outer film comprises, for example, 10-50 w% of Ni and 90-50% of Pd at a relatively high concentration of Pd. As described above, in the gradient film, the concentration of Pd in Ni continuously changes from the core to the surface. The latter can be achieved during the deposition process through changes in the deposition parameters of conventional deposition techniques, for example electrodeposition. The modulus of elasticity of the core material may be higher than that of other films.

Combinations of various materials can be used to fabricate a multilayer film stack on a stress metal spring core. They can be applied to both very thin (less than 2 μm) films and relatively thick films, for example 2 to 20 μm. Such combinations are Ni, Au, Ag, Cu, Co, Rh, Ru, Pt, Os, Pd, TiN, W or Ni-Co, Pd-Ni, Pd-Co, Co-Pt, Au-Pt, Pd-Rh , Ni-P, Ni-Mo, Ni-Co-Pd, Ni-Mo-W, Ni-PW and the like. Ni containing less than about 12% W, or Ni containing 2% Mo, or at least two materials such as Cu-Rh-Pd or Pd-Ni or Pd-Co, Ni-Co or Co-Pt, etc. Solid solutions are particularly preferred candidates for making multilayer thin film stacks because they improve the mechanical properties of the film.

Multilayer films are particularly suitable for making electrical contact with terminal / contact pads during testing and pyrotechnic processes that require relatively high current flow. It is common in the art to form frequent probe contacts on terminal pads at current levels of 250 to 500 mA. For this reason, poor contact often occurs due to excessive heat generated in the contact region. According to the modeling of the heat flow, the highest temperature reaches near the tip region of the spring. Melting of the spring tip region has also been observed in several cases. According to the present invention, such a problem can be overcome by adding a good heat conducting film, such as Cu, with a typical thickness of about 0.75-2 μm to the multilevel film stack constituting the spring. The heat can be quickly dissipated from the tip area by the Cu, thus minimizing damage during testing or hot testing. Of course, different thicknesses of good heat conducting films, eg greater than 2 μm, may serve for this purpose.

4 is a schematic of a spring finger including a Cu film to improve thermal conductivity. In order to improve heat dissipation from the spring tip, other high thermally conductive materials may be used instead of or in addition to Cu. Examples are Au, Ag, Al, and the like. In this solution, a film with high thermal conductivity can be deposited before or after the spring is lifted. If the film is electrodeposited after lifting, a high conductive film can be deposited around the core film. If the film is deposited on only one side or tip region of the spring and its vicinity, this deposition can be done before the spring is lifted and patterned.

If the probe tip to the electrical contact resistance of the contact pad is minimized, the temperature rise near the tip region of the spring is minimized. The reduction in contact resistance can be achieved by increasing the force exerted on the contact pad by the probe tip. The electrical contact resistance between the spring tip and the contact pad or terminal has been found to be less than 1π when the contact is secure and stable. The preferred range of values for good electrical contact and good heat dissipation is 0.1 to 0.2 Ohm or less.

In another embodiment of the present invention, the thin film spring can be strengthened against failure by strengthening the interface between different film layers and defects between two adjacent film layers for defect propagation. For example, the interface between the core spring material (Mo-Cr) and the adjacent layer of the Ni film can be significantly strengthened, and the bond between the two layers at the interface may result in paging-in Ni at the end of the Mo-Cr deposition. Can be made substantially stronger. Paging-in may be performed as follows. Simply before the end of the Mo-Cr deposition, Ni deposition is initiated. Then, the Mo-Cr deposition rate gradually becomes zero, during which the deposition parameters are suitably increased in the Ni deposition rate. Ni or its alloy is deposited on the Ni surface of the core for subsequent Ni or its alloy deposition on the core by other methods such as electrodeposition. As a result, a strong bond is formed and the strength of the interface is improved. The formation of this interface can be applied to improve the quality of the interface between two adjacent electrodeposited film layers. In that case, deposition of another electrodeposited film B in the vicinity of completion of deposition of the electrodeposited film A is followed, and an alloy of A _x B _1-x can be deposited using appropriate process parameters.

In another embodiment of the present invention for depositing a thin coating layer on a spring core, deposition parameters are intermittently changed during deposition to improve the quality of the coating film. It is known that depositing relatively thick film materials often results in increased pores in the film layer near the top of the film, typically at thicknesses in excess of about 1.5 to 2 μm. As a result, changing film parameters, such as changing from dc plating to pulsed plating, or changing current density during deposition, greatly improves the quality of the film. As a result, the film becomes stronger during testing or operation and resists initial failure. Changes in deposition parameters during electrodeposition can change the microstructure, such as grain size and crystal structure and film stress of the precipitate.

5 is a schematic diagram illustrating a solution to the design and manufacture of a stress metal spring according to the present invention, where 501 is an electrical pad, 502 is a via filled with metal, 503 is an insulating film such as a polymer film, and 504 Is an electrical trace, 505 is a release layer, 506 is a plated film, 507 is a spring core, 508 is a plated film on the surface, and 509 is a substrate. This design allows good electrical contact to be made with reduced force, thus substantially increasing the resistance to failure during repeated touchdowns. The fatigue life of the structure is a strong function of the applied stress. Therefore, achieving low stable contact resistance at low contact force, ie being able to lower stress in a smaller size structure, is highly desirable to improve the life and performance of the spring. Reportedly, some small springs manufactured in a manner different from the present invention, which are used for testing or high temperature inspection of electronic devices, require a contact force in the range of 2 to 150 gf. In some instances, it has been exemplified that stress metal springs having a basic structure according to the invention shown in FIG. 5 can make very good contact with much smaller forces. In these examples, some films covering the front surface of the core film, such as Ni or Ni alloys, were not very thin, more than 2 μm, and the outer surface of the spring was a relatively hard and environmentally stable material such as Pd-Co or Rh. Coated with. However, the force of 1.4 gf at the contact between these springs and Al, one of the most difficult materials to make electrical contact, formed a good, low and stable contact resistance. In fact, it has been found that for effective electrical contact between these springs and Al it is desirable that the force remain within the range of about 0.8 to 10.0 gf. Larger forces tend to damage contact pads 501 and smaller forces fail to penetrate surface oxides reproducibly. In contacting other materials such as Au, Cu and solder that do not form strong oxides, such as the material on Al, the force required to form good electrical contact is much smaller, for example 0.2 gf. Good electrical contact was made between the probe spring and the gold contact pad with a force as low as 0.01 gf. As described above, good electrical contact with low contact resistance allows testing of the circuit or device at higher currents without significant degradation of spring quality due to high thermal problems. As a result, having the structure shown in FIG. Probe springs are preferred for tests or high temperature inspections that require higher current flow. Similar springs having a multi-layered structure, for example of very thin films of less than about 2 μm, are also suitable for such tests or high temperature inspections that require higher current flow.

As mentioned above, the ability to make good electrical contact between a spring and a contact pad or terminal at a very low force brings many advantages. The microelectronics industry has introduced a low dielectric constant material and copper metallization into deep submicron integrated circuits, opening up substantial demand for low force probe contact during chip testing and high temperature inspection. Low k dielectric materials are relatively soft. As a result, the spring structure described herein is particularly suitable for applications to circuits comprising Cu films and low dielectric materials. These springs can be in good electrical contact on Cu, for example with a relatively small force of less than 1 gf. Thus, the chance of damaging circuit elements is minimized.

Another important advantage from the small force contact is related to the manufacture of interposers. As is known in the art, a probe card assembly may be connected to a probe chip (or space transformer) and a load-board (tester) for electrical connection between the IC to be tested and the tester. Interposers are often used. Cantilever type springs are attached to these interposers to facilitate electrical connection. In probe card assemblies currently available on the market, the force exerted by each of these interposer springs is relatively large, for example 15 to 30 gf. Interposers with small stress metal springs made by the present invention can be in electrical contact with opposing contact terminals with much smaller forces, for example from 0.005 to 2 gf, because the contact terminals are generally for example gold This is because it is made of a material other than aluminum. This small contact force can be applied by these springs consisting of only a core material such as MoCr without plating. Of course, in some applications a relatively thin plating layer containing gold is desirable to increase mechanical properties such as electrical conductivity of the spring or resistance to wear of the spring tip. If the contact force of the spring is small, the total force applied by the interposer with thousands of springs is significantly reduced. Thus, using the present invention, current photolithographically patterned small stress metal springs are used in constructing probe card assemblies, interposers, and assembly facilities for testing and high temperature inspection and packaging, including probe chips. This greatly simplifies by the use of these small force springs because bending, warping and alignment characters are minimized. Due to the small force exerted by the springs of the invention on the contacts to establish a good electrical connection, bulky mechanical supports and even interposers for the assembly may not be necessary in many applications. Thus, using the small force springs disclosed herein greatly increases yield and reliability, and also reduces cost and complexity.

It is known that increasing the thickness of the spring can increase the contact force of the spring against the contact pads or electrical terminals. Equations are available to calculate the force as a function of the spring's dimensions. In stress metal springs, the thickness of the core material, for example Mo-Cr, is typically kept below about 5-6 μm to facilitate lifting of the free portion of the spring after patterning to the substrate. In order to increase its thickness for applications requiring an increase in contact force, a film is subsequently deposited on the spring, for example by electrodeposition. Selective deposition of additional films on springs using photolithography or other methods is quite complex and expensive due to the non-flat structure of the springs. In the present invention, a much simpler and more effective method of depositing another film by electrodeposition is applied on a spring and, if necessary, on a circuit trace. This method does not require the use of any masking. In this case, electrical contact to the array of springs may be achieved by blanket deposition of the electrically conductive thin film on the back of the substrate or back patterning of the film to provide better control of current density. From the back. Electrical continuity is established using vias, such as 502, passing through the substrate, which are springs, adhesive layers 505, spring metal 507, traces 504, or contact pads 501. It is filled with an electrically conductive material in electrical contact with it. As a result, the film is deposited only on the electrically conductive surface that is electrically connected to the appropriate terminals of the power supply at the back of the substrate. This configuration allows for selective electroplating on all sides on the lifted spring, thus electroplating other metal structures that surround the spring and are not covered with traces and insulating material. Preferred substrates include inorganic materials such as ceramics, quartz, silicon, glass. Other substrates including organic materials such as polymers, epoxies, FR4 and polyimides can also be used within the scope of the present invention. Examples of organic material substrate groups include printed circuit boards using FR4, Dupont's Thermount and Nelco's N4000.

WO 01/48870 reports plating of materials onto a lifted stress metal spring. However, due to the non-flat structure, complicated photoresist patterning was used for the electroplating material on one side of the lifted spring. In the present invention, this method did not work well in the manufacturing process because stress is present in the film predominantly deposited on one surface of the core spring material, which affects the spring lift height. Also, apparently, due to the surface tension effect, the photoresist deposited on the free portion and the base of the spring tend to attract the lifted portion toward the base because the spring core is made very thin and lifts properly. As a result, this method is not suitable for obtaining a reproducible and controlled height for an array of springs. In the present invention, this problem is eliminated by electrodepositing the envelope of the material on the spring core without using any photoresist mask as shown in FIG. The two sides of the core spring are also fairly balanced in this case, thus minimizing the change in lift height of the spring due to plating. Thus, plating of the spring core without the use of a mask uses substrate through vias to establish electrical contact from the substrate surface opposite the surface on which the spring is located, thereby removing all core surfaces (and other electrically conductive surfaces around the spring if necessary). It is highly desirable to create an envelope of the electrodeposited film that covers it.

6 shows the spring lifted before plating, and FIG. 7 shows the spring after plating. In order to maintain adequate stress of the plated film, it is important to compensate for the change in current density that occurs when the area of the lifted spring changes. The current supply must be programmed to manage the stress in the film to compensate for changes in spring thickness that reduce the current density.

A problem that is commonly encountered in many touchdowns, for example as many as 100,000, is the formation of contact pad material for the tip region of the stress metal spring. This affects the contact resistance and the life of the spring, especially when the contact pad is made of aluminum. This problem is minimized if the probe tip area is coated with a metal or electrically conductive material that does not adhere well or at all to a contact material such as Al, for example. Examples of such coating materials are materials of the platinum group, including rhodium (Rh), palladium and ruthenium and for example palladium-nickel, palladium-rhodium, palladium-cobalt, palladium-gold-rhodium and titanium nitride, Ir And their alloys comprising two or more additives such as -Au, Ir-Pt, gold-cobalt, zirconium nitride and the like. After the stress metal spring has been released from the substrate, for some applications, even if a thin film of this coating material is deposited on the body of the probe spring for application of a smaller force and lower current, in some applications the coating is deposited only near the tip region of the spring. It is desirable to. The reason for not depositing all of the coating material on the body of the spring is to optionally be flexible in order to coat the spring tip region, for example in selecting the coating material for the desired modulus and film thickness. The presence of some coating material with a relatively large thickness in the body of the spring can affect the reliability of the spring. The present invention provides a new solution for depositing such a coating to accurately control only the tip region of the stress metal spring using techniques compatible with integrated circuit technology. In this solution, a "button", preferably consisting of a plurality of electrically conductive films, is produced in the tip region of the spring and in contact with the electrical contact pads or terminals. In one embodiment of this solution, the aforementioned coating material is deposited as the final overlap layer on the "button" before the free portion of the probe spring is released from the substrate. As a result, the problem associated with subsequent lifting of the free portion of the spring to an appropriate height is minimized, since only a small part of the spring is restrained by the coating material of the tip and the rest is bent freely and lifted. This method is used for smaller force springs that do not require additional thickness and improved spring conductivity for larger forces (MoCr springs are thin and resistant).

The process steps for producing a spring having the above described "buttoned" tip are as follows. After deposition of a stress metal spring core film such as for example Mo-Cr, a mask such as, for example, a photoresist is deposited on the core film and patterned using a technique that defines a spring such as photolithography. The spring is etched, the photoresist is removed, and an additional photo process is subsequently followed, leaving all core films except the tip region of the spring covered with a mask. Subsequently, a film such as Rh, which is later deposited on the core of the spring, as an overlapping layer, is deposited to a predetermined thickness on the exposed tip region of the spring, and then for example Pd-Ni, Pd-Rh, Pd-Co A final overlap layer comprising the coating material described above, such as Rh or TiN, is deposited to a thickness of about 1-4 μm. The thickness range of the coating layer may of course be larger, for example 1 to 20 μm, in order for the invention to work. In a variation of this embodiment, the film deposited on the tip region of the spring may also be made of a material other than the material to be deposited later on the body of the spring. In removing the mask, etching is used to cut off the lower portion of the spring and release the free portion of the spring from the substrate. Next, the top film is deposited on the body of the spring to a predetermined thickness, while protecting the tip region of the already prepared spring with, for example, a mask of photoresist or polyimide.

The thickness of the resulting tip area can be designed to be approximately equal to the rest of the lifted spring. The mask is then removed and a probe spring is obtained having a coating material of a predetermined thickness on the tip region of the spring. Although many film deposition techniques can be used to deposit the overlap layer, electrodeposition is preferred for such deposition. In another variation of this embodiment, instead of patterning the fingers of the spring after the coating film has been deposited on the tip regions of the spring, after patterning the deposited core film into the spring fingers, on the tip regions of the spring before release of the spring. Selective deposition of the overlap film may also be made. The remaining subsequent process steps are the same for both embodiments.

A preferred method of manufacturing a button on a raised plated spring such as that shown in FIG. 7 is described below. After the spring is lifted from the substrate using photolithography, the tip region of the spring is selectively coated by one or more suitable materials (button making). In this method, photoresist is deposited on a lifted spring using well known techniques such as spinning or spraying or plating. The preferred method is to spin on the photoresist. Unlike an unplated spring, a thick photoresist can be applied to the spring because the sheath of the relatively thick material on the core substantially stiffens the spring. Because of this improved stiffness, the height of the spring is not greatly affected by the application of the photoresist. The spring covered with photoresist is shown in FIG. 8. For plating of the photoresist, electrical terminals on the back of the substrate are used to connect to the power source as discussed above. The back terminal is connected to a spring on the front side of the substrate through metallized vias. Next, using photomask and photolithography techniques as shown in FIG. 9, the photoresist is substantially removed from the tip region of the spring comprising the top surface and sidewalls of the tip region. Then, as described in the foregoing sentence, using a conventional technique, preferably electroplating, a tip coating material such as, for example, Pd-Ni, Pd-Co is deposited on the tip region of the spring. Sputtering or CVD can be used, in which case a coating material is also deposited on the photoresist layer, which is later removed with unnecessary top coating material using conventional solvents leaving only the coating material on the tip area. Electroplating of the tip region of the spring not covered with photoresist allows for substantially covering the tip region. Preferred materials for the button include platinum group materials (ie Pd, Pt, Rh, Os, Ru, Ir), Ni, Co, Au, Ag. This structure is shown in FIG.

In the process described in the foregoing sentence, the tip button is plated, and then a sheath of a relatively thick Ni-like material is deposited on the core, which substantially stiffens the spring. Because of this enhanced rigidity and the relatively small area covered by the spring by the button, the spring lift height is not greatly affected by the button plating. After the tip of the button is plated, the photoresist is removed leaving the final structure as shown in FIG. Note the anchor portion 516.

Variation of the solution described in the above sentence to selectively coat the spring tip region and deposit the top film after lifting of the spring core film, in case no metalized through hole is present in the substrate to enable back connection This may also be used. In this case, a stress metal spring is first produced by an electrically conductive material such as Au, Ag or Cu, using a technique such as sputtering or electrodeposition or CVD, after the lifted spring is produced to the desired thickness, including the top film on the core film. It is deposited entirely on the substrate comprising a. This conductive layer is used to provide an electrical connection for button electroplating of the spring tip. Photoresist is then deposited over the electrically conductive surface. Using photolithography techniques as described in the foregoing sentence, the coating material is selectively deposited only on the tip region of the spring. The thin conductive material deposited prior to photoresist deposition is then removed by wet or dry etching techniques.

FIG. 12B illustrates a particular embodiment of a selectively coated spring tip region with improved spring life, where 1215 represents a tip button with a protective coating such as Pd-Co or Pd-Ni alloys, and the like. Here, the free portion 1218 of the spring is substantially tapered. As described below, in this embodiment, the life of the spring is substantially improved, and the coating material in the tip region shows no degradation during repeated touchdown.

FIG. 13 shows the results of tip (button) plating by applying a photoresist and then exposing the tip region by patterning and selectively coating the tip region by electroplating of Pd-Co alloy. In general, only a relatively small area of the spring tip may contact the IC terminals or electrical contact pads on other elements of the probe card test assembly for electrical testing or pyrotechnic operation, but all the tips may be covered with substantially plated buttons. have. Covering a large area of the spring tip by the button material provides flexibility in designing the spring and test assembly. In addition, coupling springs to the IC terminals or contact pads of electrical components for packaging applications using techniques such as soldering is greatly facilitated through the use of buttons that substantially cover the spring tips. In such a case, the button plating material is selected from the group that forms good bonds with solder such as Pb-Sn or alloys containing Sn, such as Pb-Sn commonly used in the microelectronics packaging industry. Examples of button materials or spring coating materials for forming contacts with solder or conductive adhesives in packaging applications include, for example, cobalt, nickel, gold, copper, cobalt or alloys, as well as platinum group materials such as palladium, platinum, ruthenium, and the like. There is a multilayer film stack comprising a.

The resistance of the stress metal spring to failure can be increased by designing a spring having a variable width that increases from the tip region to the base of the finger. While repeating the touchdown, most spring breaks occur near the base of the spring. Since the stresses generated during contact with the contact pads are generally the highest near the base of the spring finger, the stress near the base can be significantly reduced by increasing the width near the base area. For example, the free portion of the spring can be patterned to have a substantially trapezoidal shape. Increased resistance to failure can also be achieved by thickening the area closer to the base of the spring, which reduces stress near the spring base area during constant force.

12A and 12B are schematic diagrams illustrating a particular embodiment 1200 of a spring having a tapered variable width, where 1216 represents a fixed spring base and 1218 represents a free portion of the spring with tapering for a relatively uniform stress distribution. Indicates. By tapering the free portion 1218 of the spring, the resistance to failure of the spring is greatly increased. An important point here is that the shape of the free portion 1218 of the spring is properly formed in this case via tapering, so that bending stress is evenly distributed along the spring 1200. In addition, the tapering increases the spring's compliance. The concept thus allows the design solution to maximize the force at the minimum stress for some flexibility. Parallel sides in the base region (ie anchor) may also extend to some lifted region (ie free portion), such as 1218a, before tapering begins. FIG. 12B schematically illustrates a button and tapered spring that has been found to withstand multiple touchdowns without failure.

In an exemplary embodiment, the stress metal spring core member including the anchor portion and the free portion attached to the substrate is a high modulus material such as Mo, Mo-Cr, W, Ti-W. The core member is optionally coated to cover all exposed surfaces after the free portion of the spring is lifted. As a result, an envelope is formed comprising at least one metal film deposited by electroplating without a mask using metallized through holes in the substrate to establish electrical contact from the backside (opposite the spring side) of the substrate. The sheath balances the stress in the free portion and extends to the anchor portion without any discontinuity that mechanically weakens the film and prematurely fails. Typically, Ni or a Ni alloy is deposited on the core member. If desired, additional films such as Pd alloys are optionally electroplated onto Ni. Selective deposition of an additional layer of palladium alloy film onto the tip region of the spring is done using conventional photolithography and electrodeposition (electroplating and / or electroless plating) or deposition techniques such as sputtering or CVD. Typical thickness of Mo-Cr is 4 μm. The thicknesses of the electroplated nickel and palladium alloy films on both sides of the Mo-Cr film are 2-20 μm and 1-10 μm, typically 12 μm and 4 μm, respectively. In this case, the elastic modulus of the film decreases from the core toward both sides of the spring. For example, the thickness of a button comprising an additional deposit of palladium alloy film in the contact tip region is 1-20 μm, with a typical value of 12 μm.

Another feature of the invention is the elimination of stress concentration points on the spring surface. It has been observed that failure of a spring, such as a crack, often begins at the surface during repeated touchdowns. Therefore, surface roughness needs to be minimized. As shown in Figure 5, many roughnesses on the sidewalls of the lifted spring are generated during patterning of the core film consisting of Mo-Cr, W or Zr-Ni, for example by wet etching. A top film, such as 506, subsequently deposited on core 507 follows the rough contour of the side, resulting in a rough surface on the side of the finished spring structure. According to the present invention, forming the spring core pattern by dry etching comprising ionized species minimizes this roughness. In using electroplating to form the top film, roughness is also minimized using a process of sequential plating and reverse plating to form the thickness of the spring. The reverse plating parameter is adjusted such that only a portion of the plated thickness is removed during reverse plating. Also, by electropolishing, chemical or electrochemical polishing, first polishing the side of the wet etched core 507 or the side of the fully plated spring can minimize roughness.

In another embodiment, a stand-off is provided on a substrate or electrical element such that a spring in which the core film is entirely covered with the top film precipitate is allowed by the designed height and position of the standoff. Or with the maximum overdrive on the terminal.

The aforementioned solution can be used for the manufacture of a variety of other cantilever springs other than stress metal springs that are partially lifted due to intrinsic stress gradients in the film. One of the important points regarding the performance of these other cantilever springs is that the tip ends of the springs are pressed to contact the contact pads, i.e. input / output (I / O) pads of the wafer or other substrate, or elements of the test or pyrometer assembly. In this case, since the stress in this region is the highest, the propensity for failure, for example, near the base or the angled end of the cantilever spring, is deformed or cracked. Mathematical representations are available to represent the effect of spring length on stress near the base region. When the spring is pressed in contact with the contact pad, the length of the spring is now about 700 to 2,000 μm to minimize the stress in the base area while bending the spring to increase the resistance to failure during repeated touchdowns. It is designed relatively large. However, this cantilever for some current and next generation testing and high temperature inspection of micro integrated circuits where the spring probe array is matched with a very dense device I / O pad array with more dense pitches, for example about 20-50 μm. Limit the application of the spring. As a result, it is highly desirable to find a means for forming shorter springs with a tighter pitch that is strong enough to withstand higher stresses, especially without failure near the base region.

The free portion of the cantilever type spring needs to be thicker in order to increase the spring constant to exert the required force at the spring contact point against the contact pad. In some embodiments, thicker springs may be formed by electroplating one or more metals or alloys thereof, such as nickel or nickel alloys or palladium alloys, on photolithographically patterned freestanding spring cores such as Mo-Cr alloys. Is formed. In some other embodiments, the spring is patterned using photolithography and manufactured by electroplating a relatively thick layer of at least one metal or metal alloy film, such as nickel or nickel alloy, on the seed layer. In many of these embodiments, a button type contact structure is also provided in the contact tip area to improve contact characteristics and maintain contact integrity during touchdown repeats during wafer testing and high temperature operation. However, such embodiments still require a relatively thick film to construct the body of the spring to apply the required contact force at the contact tip end. For relatively shorter springs of about 100 to 700 micrometers in length, increasing the thickness of the spring results in higher stresses near the base end resulting in shorter spring life.

The solution for producing shorter types of springs with or without buttons such as the contact structure at the tip region of the springs is described below, where the strength at the base or body area of the springs is strengthened against mechanical failure such that Spring performance, strength, durability and lifespan are greatly improved.

14A and 14B are two cross-sectional views of a typical freestanding non-stressed metal cantilever spring in accordance with the present invention. The freestanding cantilever spring includes a base region 1401 at one end attached to the electrical contact pad 1402 of the substrate 1403, a contact tip region 1404 at the other end of the spring, and a contact tip region 1404. Combined button 1406 and a body deposited with Ni film 1408 and Pd alloy film 1409. The spring length may extend from the substrate surface while being substantially parallel to the surface of the substrate to which the spring is attached or at an angle to the surface. Typically, the base 1401, the tip 1404 and the body of the spring are made of the same material in the same operation using film deposition techniques such as, for example, electroplating, sputtering or CVD.

Contact tip region 1404 includes a button type contact structure 1406 to facilitate reliable and durable contact, which selectively deposits a film on contact tip region 1404 as an integral part of the tip region. It can be made by or made separately and attached to the tip area. Likewise, base region 1401 may be attached to a post that may be fabricated integrally with a spring or separately fabricated and joined to the base using conventional techniques such as soldering, soldering, and the like. To fabricate the post in its entirety, the film may be polished after the selective deposition of holes into the sacrificial substrate using techniques such as electroplating.

Having a button type contact structure 1406 in the spring tip region 1404 is useful for achieving reliable and durable electrical contact to the opposing contact pads in a wafer test or pyrometer assembly. In this case, an appropriate material may be selected that has the desired contact properties and thickness in constructing such a button, which is not essential but may comprise the same material as the body 1405 or base 1401 of the spring. However, the choice of material for each of the three parts should be made to give toughness to all parts of the spring so that they withstand wafer test and hot inspection processes while repeating the touchdown without failure. Many materials suitable for a variety of electroplating have been used to make cantilever type splices. Such materials include, for example, nickel and its alloys, gold, rhodium, Pd and its alloys, elements of copper, platinum groups and their Alloys, titanium, molybdenum and alloys thereof, and the like. However, the challenge remains to produce shorter springs with the required toughness. Non-stressed metal cantilever springs manufactured today are relatively long, for example between 1 and 2 mm. The main challenge in the art is to support permanent drives in the microelectronics industry to create deep sub-micron integrated circuits with greater circuit density and smaller pitch between input / output terminals. To find a means to make an array of springs that are much shorter and more robust.

The present invention allows such an array of tough contact springs to be manufactured by applying the principle of selection of special materials to the construction of button- or non-button springs comprising metal films. Applying these principles, the selection of the appropriate material provides a special method of film deposition, thus producing contact springs with the desired toughness.

The special material selection principle known to have a very important effect in improving the performance and reliability of the spring is as follows. A multilayer film comprising a base, a tip region of the spring and three parts of the body and a button is deposited with a film of low modulus near the surface of the spring in contact with the IC terminal for testing, and a film of progressively high modulus facing the It has a gradient material composition to be deposited towards the surface. The mechanical strength of the button is not as important as the mechanical strength of the body and base area of the spring, which determines the strength of the spring. However, in accordance with the teachings of the present invention, the button film has, if necessary, an elastic modulus of the film on the button surface having a lower elastic modulus than the lower film layer, which elastic modulus gradually increases as it moves away from the button surface. It may be chosen. This gradient change in composition and modulus of elasticity from the contact surface of the spring to the opposing surface disperses the stress at critical locations, suppressing damage to the spring, in the form of continuous or discontinuous steps over the interface between two different materials. It can be used to As a result, the life of the spring increases. This is caused by mechanical failure in the spring anywhere, including the base 1401 of the spring, when the tip 1404 of the spring is pressed to contact a contact pad on another substrate, such as a semiconductor wafer or other element of a test or pyrometer assembly. Increase resistance to

According to the above principle, one embodiment of a non-stressed metal cantilever spring has a nickel film as the base layer and a nickel alloy film containing about 20% palladium or palladium as the top layer, where nickel is This is because the modulus is higher than that of the palladium alloy. In general, other films may be deposited to form a multilayer spring, so long as the selection principle is applied to determine the deposition sequence. Additionally, very thin film layers may be deposited between the two main film layers if desired to enhance the strength or tack of the interface. For example, as is well known in the art, gold or nickel or rhodium strikes can be used for this purpose. In this case, the button 1406 on the tip region 1404 may comprise an additional film layer of the palladium alloy. The button 1406 may be manufactured as an integral part of the contact tip region 1404 or may be separately attached to the tip region 1404.

Springs as shown in FIGS. 14A and 14B are typically deposited on the sacrificial layer and then removed to provide a freestanding cantilever spring. Substrate 1403 may also have multilayer metal and electrically conductive blind vias or through vias such as 502 shown in FIG. 5. Films 1408 and 1409 and other additional layers are deposited by conventional techniques such as electroplating. If desired, a suitable thin adhesion promoting layer and / or seed layer comprising a material such as titanium may be deposited prior to the deposition of the electroplating layer. The thickness of each film layer is determined by the desired contact force or spring constant, which can be calculated from various mathematical expressions. Various spring sizes in the thickness range of 1-50 μm may be used, for example, based on design requirements for force and pitch, and the like. Taking the total spring thickness of 30 [mu] m as an example, the thicknesses of the nickel and palladium alloys in this embodiment are 25 [mu] m and 5 [mu] m, respectively. In this case, the thickness of the additional palladium layer at the button may be 3 to 20 mu m. Note that the above figures are only used as examples. As long as the basic principle is satisfied, free fluctuations in the value to ensure the robustness of the spring are allowed.

In another embodiment, the core film consists of molybdenum-chromium alloy or titanium-tungsten or molybdenum-tungsten, and top layers of nickel and palladium alloy films are sequentially deposited. In this case, the button 1406 on the tip region 1404 includes the palladium alloy of additional deposition thickness, as above. The button 1406 may be fabricated by selectively depositing an additional thickness of palladium alloy layer on the region 1404 using photolithography. The discussion of exemplary thickness ranges, deposition techniques, adhesion promotion layers, seed layers, and the like, in the foregoing sentence also applies in this case.

As discussed above, the film of this embodiment of a non-stressed metal cantilever spring may be selectively deposited with pressure stress to further improve the robustness. The toughness is further improved by properly selecting the film deposition parameters such that the film's grain size is very small, from 3 to 500 nm. Examples of such deposition parameters include the concentration of the additives in the electroplating bath, the current density and the temperature.

The interconnect devices and associated manufacturing methods described above are suitable for a variety of applications including testing of electronic devices, wafer-level high temperature inspection and packaging of electronic devices. The electronic device includes devices such as integrated circuits, liquid crystal displays, MEMS, printed circuit boards, or any combination thereof. Packaging involves coupling and establishing an electrical connection between two elements or a substrate using the contact spring elements described above, where the coupling may be made with or without solder or conductive adhesive.

Metric Terms and Abbreviations for Chemical Elements

Μm-microns = 10 ^-6 meters

nm-nanometer, or millimeter-micron = 10 ^-9 meters

Ag-silver

Al-aluminum

Au-gold

Co-cobalt

Cr-Chrome

Cu-copper

Mo-molybdenum

Ni-nickel

Pb-lead

Pd-Palladium

Pt-platinum

Rh-rhodium

Ru-ruthenium

Sn-tin

Ti-titanium

W-tungsten

The invention applies to all types of small springs. Preferred embodiments disclosed herein are examples only and do not limit the invention. Other modifications and variations of the present invention will be apparent to those skilled in the art from the foregoing detailed description. Although only specific embodiments of the present invention have been specifically described herein, it will be apparent that numerous modifications may be made without departing from the spirit and scope of the invention.

Accordingly, the invention is limited only by the claims contained in the claims.

Claims (61)

An interconnect device for establishing electrical contact between two components, At least one elastic core member, The elastic core member includes an anchor portion and a free portion attached to the substrate, The substrate includes at least one through-via filled therein with an electrically conductive material, The free portion initially contacts the substrate and away from the substrate due to an inherent stress gradient in the core upon release, The core member is enveloped electrodepositedly with at least one layer covering all exposed surfaces of the core member. Interconnect device. The method of claim 1, Wherein said envelope comprises an electroplated film. The method of claim 1, Wherein the free portion is substantially tapered or substantially trapezoidal in shape with a progressively decreasing width toward the tip of the probe over the substantial length of the free portion. The method of claim 1, The at least one layer is selected from the group of materials comprising at least one of nickel, palladium, platinum, rhodium, ruthenium, osmium, iridium, gold, silver, copper, cobalt, aluminum, tungsten, and any alloy thereof. Interconnect devices. The method of claim 1, At least one average grain size of said at least one layer is in the range of 3 to 500 nm. The method of claim 1, At least one layer is electroplated with intrinsic compressive stress. The method of claim 1, At least one layer near the surface of the core member wrapped in the electrodeposited manner has a lower modulus of elasticity than the core surrounded by the layer. The method of claim 1, Wherein the sheath comprises a plurality of different sequentially deposited films. The method of claim 8, The electrodeposited film generally has a gradual decrease in elastic modulus of the deposited film toward the outermost surface from the innermost core, or substantially discontinuously toward the outermost surface from the innermost core. Interconnect devices deposited in a reducing manner. The method of claim 1, And a film layer optionally provided over said electrodeposited core member in a probe tip region. The method of claim 10, Wherein said film layer comprises at least one of said groups of palladium, rhodium, platinum, iridium, osmium, ruthenium, cobalt, nickel, gold, and alloys thereof. The method of claim 1, Wherein said free portion has a size in the range of 10 μm to 1000 μm in length, 3 μm to 500 μm in width, and 0.1 μm to 40 μm in thickness. The method of claim 1, Wherein the outermost layer of the at least one layer comprises a platinum group material consisting of Pd, Pt, Ir, Rh, Ru, and Os, and any one of nickel, gold, and copper. The method of claim 1, Wherein the substrate comprises any one of ceramic, glass, silicon, quartz and organic materials. The method of claim 1, Wherein said core member comprises any one of Mo, Cr, Ti, W, Zr, Mo-Cr, and Ti-W. A method of manufacturing a plurality of miniaturized springs on a substrate, each miniature spring comprising an electrically conductive core member, the core member contacting the anchor portion, initially contacting the substrate, and releasing. A free portion away from the substrate due to an inherent stress gradient in the core, the free portion having a tip region at its end, and the anchor portion having a plurality of metalized through vias. In the small spring manufacturing method is fixed, Electroplating the spring core member with at least one film layer to cover the entire surface of the core member including the free portion without using a mask, Electroplating of the core member is performed using through vias in the substrate to establish electrical contact to the core member from the side of the substrate opposite the side on which the core member is located. How to make a compact spring. The method of claim 16, At least one film layer is electroplated by inherent compressive stress. The method of claim 16, Wherein said at least one film layer is electroplated with an average particle size in the range from 3 to 500 nm. The method of claim 18, Wherein said particle size of at least one electroplated film is controlled by altering the composition and / or current density of additives in said electroplating bath during plating. The method of claim 16, The at least one film layer is any one of Pt, Pd, Rh, Ir, Ru, Os, cobalt, nickel, gold, silver, copper, aluminum; And a material group comprising an alloy comprising at least one of the group consisting of Co, Ni, Au, Cu, Ag, Al, Pt, Pd, Rh, Ir, Ru, Os, W. The method of claim 16, Selectively coating said tip region to form a contact button after said electroplating of a core member, The contact button comprises at least one electrically conductive material that is not strongly adhered to an opposing contact pad or terminal, And the tip region is optionally selectively coated to form the contact button before the free portion is released from the substrate or after the free portion is released from the substrate. The method of claim 21, Wherein said at least one electrically conductive material comprises at least one of a group consisting of palladium, rhodium, platinum, iridium, osmium, ruthenium, cobalt, nickel, gold, silver, copper and alloys thereof. The method of claim 16, Forming a pattern of the core film by dry etching. The method of claim 16, Polishing the core film prior to deposition of the layer. The method of claim 16, Polishing the outermost surface using any of an electropolishing, chemical polishing, and electrochemical polishing process. An interconnect device for establishing electrical contact between two components, At least one elastic core member, The elastic core member includes an anchor portion and a free portion attached to a substrate having a multilevel metallization having at least one metallized via, The free portion initially contacts the substrate and away from the substrate due to an inherent stress gradient in the core upon release, The core member is enveloped electrodepositedly with at least one layer covering all exposed surfaces of the core member. Interconnect device. An interconnect device for electrically connecting two components, At least one elastic core member comprising an anchor and a free portion attached to a substrate, the free portion initially contacting the substrate and upon release, the core. The at least one elastic core member away from the substrate due to an inherent stress gradient in it, At least one layer covering the core member in an electrodeposition manner to form an envelope covering all the exposed surfaces of the core member; A film layer optionally provided in the tip region of the probe onto the electrode body wrapped in the electrodeposition manner; Interconnect device. The method of claim 27, Wherein said envelope comprises an electroplated film. The method of claim 27, Wherein the free portion is substantially tapered or substantially trapezoidal in shape with a progressively decreasing width toward the tip of the probe over the substantial length of the free portion. The method of claim 27, The at least one layer is selected from the group of materials comprising at least one of nickel, palladium, platinum, rhodium, ruthenium, osmium, iridium, gold, silver, copper, cobalt, aluminum, tungsten, and any alloy thereof. Interconnect devices. The method of claim 27, At least one layer is electroplated with intrinsic compressive stress. The method of claim 27, At least one average grain size of said at least one layer is in the range of 3 to 500 nm. The method of claim 27, The sheath comprises a plurality of different sequentially electrodeposited films, The electrodeposited film is interconnected in which the elastic modulus of the deposited film generally decreases progressively from the innermost core toward the outermost surface or substantially discontinuously decreases from the innermost core toward the outermost surface. Device. The method of claim 27, Wherein the anchor portion is attached to a substrate having a plurality of through vias filled with an electrically conductive material. The method of claim 27, Wherein said film layer comprises at least one of said group of materials consisting of palladium, rhodium, platinum, iridium, osmium, ruthenium, cobalt, nickel, gold, silver, copper, and alloys thereof. The method of claim 27, Wherein said free portion has a size in the range of 10 μm to 1000 μm in length, 3 μm to 500 μm in width, and 0.1 μm to 40 μm in thickness. A method of manufacturing a plurality of miniaturized springs on a substrate, each miniature spring comprising an electrically conductive core member, the core member contacting the anchor portion, initially contacting the substrate, and releasing. And a free portion away from the substrate due to an inherent stress gradient in the core, the free portion having a tip region at its end and the anchor portion fixed to the substrate. In Electroplating the spring core member with at least one film layer to cover the entire surface of the core member including the free portion, without using a mask, Selectively coating the tip region to form a contact button after electroplating of the core member, The contact button comprises at least one electrically conductive material that is not strongly bonded to opposing contact pads or terminals. How to make a compact spring. The method of claim 37, At least one film layer is electroplated by inherent compressive stress. The method of claim 37, Wherein said at least one film layer is electroplated with an average particle size in the range from 3 to 500 nm. The method of claim 39, Wherein said particle size of at least one electroplated film is controlled by altering the composition and / or current density of additives in said electroplating bath during plating. The method of claim 37, The material used for the inner layer has a higher modulus of elasticity, The material used for the outer layer has a lower modulus of elasticity, The modulus of elasticity of the layer decreases gradually from the innermost layer to the outermost layer, or discontinuously decreases from the innermost layer toward the outermost layer. The method of claim 37, The at least one film layer includes Pt, Pd, Rh, Ir, Ru, Os, cobalt, nickel, gold, silver, copper, aluminum, tungsten; And at least one of these alloys. The method of claim 37, Wherein said substrate comprises any one of ceramic, glass, silicon, quartz and organic materials. The method of claim 37, The core member is a miniature spring manufacturing method comprising any one of Mo, Cr, Ti, W, Zr, Mo-Cr, and Ti-W. The method of claim 37, Electroplating of the core member is performed using through vias in the substrate to establish electrical contact to the core member from a side of the substrate opposite the side on which the core member is located. The method of claim 37, The tip region is selectively coated to form the contact button before the free portion is released from the substrate or after the free portion is released from the substrate. The method of claim 37, The at least one electrically conductive material is Pt, Pd, Rh, Ir, Ru, Os, cobalt, nickel, gold, silver, copper, tungsten; And at least one of a group of materials comprising alloys thereof. The method of claim 37, Forming a pattern of the core film by dry etching. The method of claim 37, Polishing the core film prior to deposition of the layer; Selectively polishing the outermost surface using any of an electropolishing, chemical polishing, and electrochemical polishing process. A method of manufacturing a small spring on a substrate, each said small spring comprising an anchor portion and a free portion, said free portion having a tip region at its end, the width of the spring from the vicinity of the anchor portion toward the tip region. In the method of manufacturing a small spring that gradually decreases, Depositing a core film member; Patterning the body of the core film member to form the anchor portion and the free portion; Releasing the free portion from the substrate; Depositing at least one top film layer on the core film member covering the entire surface of the core film member; Forming a photoresist film on the core film member coated with the at least one top film; Patterning the photoresist film to expose an area on the tip region coated with the at least one top film; Coating the exposed tip area covered with the at least one top film layer with an electrically conductive contact material that minimizes contact adhesion that occurs when the touchdown is repeated; Removing the photoresist film from the core film member Small spring manufacturing method comprising a. 51. The method of claim 50 wherein The electroplating is performed using through vias in the substrate to establish electrical contact to the spring from the side of the substrate opposite the side on which the spring is located. 51. The method of claim 50 wherein At least one top film layer is electroplated with inherent compressive stress. 51. The method of claim 50 wherein Wherein said at least one top film layer is electroplated to an average grain size in the range of 3 to 500 nm. The method of claim 53, wherein The particle size of the at least one electroplated film is controlled by changing the composition and / or current density of additives in the electroplating bath during plating. 51. The method of claim 50 wherein The material used for the inner film layer has a higher modulus of elasticity, The material used for the outer film layer has a lower modulus of elasticity, The elastic modulus of the film layer gradually decreases from the innermost film layer toward the outermost layer or discontinuously decreases from the innermost film layer toward the outermost film layer. 51. The method of claim 50 wherein And the contact material is deposited by any one of electroplating, sputtering and chemical vapor deposition. The method of claim 56, wherein The electroplating is performed using through vias in the substrate to establish electrical contact to the spring from the side of the substrate opposite the side on which the spring is located. 51. The method of claim 50 wherein The at least one top film layer on the core film member may comprise Pt, Pd, Rh, Ir, Ru, Os, cobalt, nickel, gold, silver, copper, aluminum, tungsten; And at least one of these alloys. 51. The method of claim 50 wherein The contact material is a small spring manufacturing method comprising any one of Co, Ni, Au, Cu, Ag, Pt, Pd, Rh, Ir, Ru, Os. 51. The method of claim 50 wherein Wherein said substrate comprises any one of ceramic, glass, silicon, quartz and organic materials. 51. The method of claim 50 wherein The core film member is a small spring manufacturing method comprising any one of Mo, Cr, Ti, W, Zr, Mo-Cr, and Ti-W.