CN102543784A - Solid-state hot-compression low-temperature bonding method using nickel micro needle cones - Google Patents

Abstract

The invention provides a solid-state thermocompression low-temperature bonding method using nickel micro-needle cones. A layer of metal nickel covered with needle-cone shapes is prepared on one side of the solder joint to be bonded, and solder is used on the other side. The device is used to align the electrical interconnect solder joints, heat the solder joints to a certain temperature not higher than the melting point of the solder cap, and apply a bonding pressure for a certain period of time to achieve the mosaic bonding of the needle taper and the solder at the interconnection points , A thin layer of precious metal is electroplated on the nickel microneedle cone layer to prevent the surface from being oxidized before bonding. After the bonding is completed, the solder joint is heat treated at a certain temperature for a period of time to achieve diffusion reaction and eliminate holes. The method provided by the invention can overcome some defects of the prior art in the application of the new packaging technology, avoid the heat damage to the device caused by the reflow process temperature, and the problems of solder spreading and solid-liquid phase rapid response in fusion welding.

Description

A solid-state thermocompression low-temperature bonding method using nickel microneedle cones

technical field

The invention relates to the field of semiconductor chip packaging, in particular to a method for realizing solid-state interconnection and bonding between components through the use of a metal layer with a special needle cone shape on the surface.

the

Background technique

The micro-interconnection technology of semiconductor chip packaging is constantly innovating. Now the interconnection technologies in chip manufacturing mainly include: lead frame type; wire bonding; ball array; QFN; chip flip chip; bump bonding; load; 3D Packaging and other technologies. The innovation of electrical interconnection technology is the key to the development of microelectronics technology. The traditional fusion bonding technology is to control the temperature to make the metal at the bonding point melt and wet the two sides of the bonding point. After cooling, the bonding point solidifies, so as to obtain good welding. , such as reflow soldering.

Traditional reflow soldering and other processes need to increase the soldering temperature above the melting point of the solder. The high temperature environment will have a bad impact on some chips or substrates and reduce the reliability of the product. Alternative lead-free solders have not been able to achieve the same or lower soldering temperatures as the high-lead bumps used until now in the chip-to-package substrate flip-chip process require the use of environmentally hazardous lead. The method of melting the solder also needs to prevent bridging between solder joints.

In order to achieve the desired bonding strength, organic substances such as fluxes and adhesives are sometimes required. Flux needs to be applied to at least one surface to be bonded, and flux includes a vehicle and an activator. The flux medium serves to isolate the surface of the solder from the atmosphere during the second reflow, reducing the risk of high-temperature oxidation of the solder. The activator is usually an organic acid or an inorganic acid, which is used to remove the oxide film on the solder surface to improve wetting sex. After the soldering is completed, the flux or flux residue needs to be removed, usually including cleaning the package with a solvent, or going through a baking process to volatilize the residual solvent or low-boiling point flux or flux residue. Flux application and residue removal take production time, and the smaller the chip-to-chip or chip-to-substrate gap, the more difficult it is to completely remove the flux residue.

It is a major trend in the development of chip interconnection technology to seek low soldering temperature. There are now numerous relevant literature and patents describing chip-to-substrate or chip-to-chip stack interconnection processes by non-fusion methods. These include the use of single metals or alloys with low melting points (such as indium alloys, etc.), mechanical methods to embed metal blocks or metal bumps, active reaction layers, and low-temperature sintering of nanoparticles. Generally speaking, solid-state electrical interconnection can significantly increase the interconnection density because it avoids fusion soldering, does not require flux, and can eliminate the adverse effect on bond strength and reliability that occurs between the solder and the pad on the substrate during the fusion process Excessive interfacial reaction, and due to the reduction of process temperature, the process flow and cost are also reduced.

There have been many reports on copper-copper solid-state bonding, among which surface-activated bonding (SAB) technology can realize atomic-level connections between various metals at temperatures as low as room temperature. The copper surface used to achieve surface activation bonding is generally finely chemical-mechanical polished to achieve nanoscale flatness, and the ways to obtain a highly activated metal surface include argon atoms, ions, and plasma treatment. After surface oxides and contamination are removed, the activated chip or wafer surface requires vacuum protection to control the rate of re-oxidation and direct bonding at higher vacuum levels. A series of high-planarity metal-metal direct bonding technologies based on surface activation, including copper-copper solid-state bonding, have relatively high requirements on wafer processing technology and are often used for wafer-level interconnection.

In response to the high operating temperature of certain devices, new bonding materials and technology systems have been developed to replace tin-based solders that cannot withstand high temperatures. For example, metal indium is considered to be a promising solder due to its low melting point. Low-temperature soldering metals, the current research on the use of indium in the packaging field is mainly reflected in the use of indium and other solder metal layers, such as silver, tin, copper, gold, etc., to react with intermetallic compounds with higher melting points. For example, using a multi-layer structure of silver and tin film at about 180 ° C with contact pressure, silver is supersaturated in liquid indium to generate solid-phase products, so that the soldering process temperature is lower than that of traditional lead-free solder.

The bonding technology realized by using nano-metal particles has also been widely reported. The most commonly used is nano-silver particles. When the diameter of the metal particles reaches the nanometer level, the sintering temperature decreases significantly with the reduction in size and the increase in surface energy. Sinter bonding at a temperature much lower than that of fusion welding, even as low as room temperature, to obtain solder joints with high temperature stability. The preparation of nano-silver particles can be obtained by drying the solvent in the gel. For silver particles with a diameter of about 100 nm, the bonding can be carried out at a temperature of 300 °C and a pressure of 25 MPa. The shear strength obtained Above 10 MPa. This method has a wide application prospect in high-power components and large-area chip array packages because the solder joints have relatively high electrical and thermal conductivity.

the

Contents of the invention

Aiming at the technical problems existing in the above-mentioned prior art, the present invention proposes a solid-state thermocompression low-temperature bonding method using nickel microneedle cones, which can overcome some defects of previous processes in the application of new packaging technology and avoid reflow The thermal damage caused by the soldering process temperature to the device, as well as the problem of solder spreading and rapid solid-liquid phase response in fusion soldering.

In order to achieve the above object, the technical scheme adopted in the present invention is as follows:

A method of solid-state thermocompression low-temperature bonding using nickel microneedle cones, comprising the following steps:

1) Select components to be bonded with matching electrical interconnection pads;

2) Form a bump whose surface part is made of a soft first metal and whose bottom part is made of a second metal on one side of the pad of the couple to be bonded;

3), preparing a nickel microneedle cone layer on the pad on the other side of the couple to be bonded;

4), bonding the components to be bonded, including aligning the pads on the surface of the couple to be bonded, so that a plurality of bumps with soft metal are matched with each nickel microneedle cone area on the other side surface; and aligning the contact area Heating to a first temperature and bringing the two sides into contact completes electrical interconnect bonding at the pad region.

Electrodeposition (including but not limited to electroless plating, vapor deposition, etc.) is used to place metal blocks in the electrical interconnection area of components (such as flip-chip substrates, or PCB side pads of ball grid array packages, and patterned by photolithography , chemical corrosion and other methods) to prepare the nickel microneedle cone layer; by controlling the electrodeposition parameters including time, current density, and additive concentration, the height of the needle cone is controlled from 200 nanometers to 2000 nanometers.

After the nickel microneedle cone film is prepared, an anti-oxidation layer is prepared on the surface. The anti-oxidation layer is an oxidation-resistant metal or alloy at high temperature, with a thickness of about several nanometers to tens of nanometers, and does not change the surface morphology of the needle cone, including but not Limited to electroplating and vapor deposition methods;

This precious metal can be Au, Pt, Ag, Pd;

Use the adapter to align the couple to be bonded so that the well-shaped needle cone film area matches and aligns with the solder bump area one by one;

Heat the aligned bonding couple to a suitable temperature, apply a bonding pressure, wherein the bonding pressure needs to be maintained for a few seconds to a few minutes during the first temperature, and then release the bonding pressure, the holding time is determined by the type of solder metal, temperature, bond It is determined by the optimization results that meet the pressure requirements.

According to the specific use occasion, select this temperature within the range of 5-100 °C lower than the melting point of the solder metal;

The bonding pressure is generally between 1 - 20 MPa, depending on the bonding temperature;

The time is generally between 5 s - 20 min, depending on the bonding pressure and bonding temperature;

The second metal under the bump is prepared by an electrodeposition method;

Wherein the first metal cap on the surface of the bump has a relatively low melting point and is prepared by an electrodeposition method;

The heating to the first temperature can be through contact or non-contact heating, the first temperature does not exceed the melting point of the first metal and the solder metal, and the first temperature is determined by the optimization result of the first metal type and the bonding pressure requirement ;

Place the couple to be bonded in the first and second fixtures of the thermocompression bonder respectively, keep the temperature lower than the first temperature, and move one of the first or second fixtures or both of them to make one side more A soft metal bump and the pad metal block prepared with micro needle cones on the surface of the other side are in contact with each other, and the temperature is rapidly reached and maintained by the heating device, while pressure is applied between the first and second fixing devices and Hold until bonding is achieved at the point of contact and remove the bonded component from the adapter;

Heat treatment at the second temperature for a period of time t to improve bonding properties

This temperature is generally lower than the bonding process temperature.

Because the nickel microneedle cone structure has the characteristics of large real surface area, high reactivity at the micro-nano scale, and special sharp structure and array morphology, it has many new functional properties and can be applied in the electronic packaging industry. The present invention utilizes it to achieve good mechanical engagement with the solid lead-free solder cap that is greatly softened at a higher temperature, and the huge real surface area can promote the interdiffusion of the bonding interface to improve the bonding force and the like.

The solid-state thermocompression bonding method using nickel microneedle cone disclosed by the present invention is to make the solder layer and the nickel microneedle cone film layer mechanically occlude and diffuse under the condition of a temperature lower than the melting point of the solder and a certain pressure. realized by the reaction. The advantages and positive effects of this method are: the solder does not melt during the process, the solid-state bonding can improve the interconnection density and product reliability, has controllable interface reaction characteristics, and does not require organic substances such as flux, thus simplifying the process flow.

Detailed ways

Below in conjunction with specific embodiment the present invention is described in further detail:

Example 1:

    Under-bump metallurgy (UBM), copper pillar bumps, nickel barrier, and bump surfaces formed on bare die with I/O pads by standard photolithographic patterning, sputter deposition, and electrochemical deposition A typical copper pillar bump size is 60 μm in diameter and 40 μm in height. A typical nickel barrier layer thickness is about 1 μm. A typical tin layer thickness is 5 μm with a height difference of less than 0.5 μm. The nickel microneedle cone layer and the surface anti-oxidation gold layer were prepared by chemical deposition or electrochemical deposition on the pad area of the flip-chip substrate. The overall thickness was about 5 μm, the surface needle cone height was about 1 μm, and the gold thickness was about 10 nm. This thickness of gold plating does not affect the needle cone topography. Fix the chip, which has been washed with acid to remove the oxide layer on the surface of the bump, and the substrate face-to-face and fix it on the flip-chip bonder and align it. The temperature is quickly raised to the bonding temperature of 180 ° C, and at the same time, the bonder applies a pressure of 10 MPa, etc. Effective static pressure was maintained for 5 minutes to complete the preliminary bonding. During the initial bonding process, the nickel micro-needle cone with higher hardness penetrates the tin block, the hardness of the solder layer decreases significantly at high temperature, the creep rate accelerates, and the micro-needle cone forms a mosaic through plastic deformation to form a mechanical bond. The deformation caused by thermal compression during this process is about 1 - 3 μm. After the preliminary bonding is completed, the chip is heat-treated in a protective atmosphere at 140°C for 6 hours. During this process, the tightly bonded nickel and tin react at the interface to form a certain thickness of intermetallic compound layer. Holes are eliminated by diffusion.

Example 2

The front I/O pads of the bare chip with I/O pads on the front side and through-silicon vias (TSVs) to the device side on the back form the under-bump metal layer (UBM) and tin layer, typically tin The layer thickness is 2 - 5 μm, and the height difference is less than 0.5 μm. The chip is usually thinned to less than 100 μm, and the nickel microneedle cone layer and the surface anti-oxidation gold layer are prepared on the surface of the ground and exposed TSV filling metal. The overall thickness is about 5 μm, and the height of the surface needle cone is about 1 μm. The thickness is about 10 nm. After using plasma to remove the surface oxide layer and contamination particles, two or more silicon wafers with this structure are stacked and fixed in the bonding machine, and the temperature is raised to a bonding temperature of 180 ° C. At the same time, the bonding machine applies 7.5 The equivalent static pressure of MPa is maintained for 5 minutes to complete the initial stacking bonding. After completing the preliminary bonding, heat-treat the chip in a protective atmosphere at 140°C for 6 hours to improve the bonding strength.

Example 3

Prepare the nickel microneedle cone layer and the surface anti-oxidation gold layer on the metal block of the pad area of the printed circuit board (PCB) for ball grid array (BGA) surface mounting, the overall thickness is about 5-10 μm, the surface needle The cone height is about 1-2 μm, and the gold thickness is about 10 nm. The BGA package planted with tin alloy solder balls with a size of 300 - 800 μm is pickled to remove the oxide layer on the surface of the solder balls, and fixed and aligned with the PCB in the bonding machine, and the temperature is raised to a bonding temperature of 180°C , and at the same time, the equivalent static pressure of 10 MPa is applied by the bonding machine, and it is kept for 5 minutes to complete the preliminary stacking bonding. After the preliminary bonding is completed, the chip is placed in a 140°C protective atmosphere for heat treatment for 6h.

In the above description, many specific details are set forth for the purpose of illustration, but the protection scope of the present invention is not limited thereto, and the present invention may be practiced without completely following the details of the procedures or tools provided herein.

For example, the stud bump material can be electrodeposited nickel but not limited to copper, and the solder cap material can be a low-melting-point metal such as indium, or other alloys with a lower melting point. For die-to-substrate flip-chip interconnects and multi-die stacked vertical interconnects, the positions of the bump side and the pin-taper side can be interchanged. It is easy for those skilled in the art to implement the content of the claims of the present invention by using other equipment even without using a thermocompression bonding machine. Similarly, the matching sequence of temperature requirements and pressure in the bonding process can also be adjusted according to the needs of actual operations, for example.

Claims (11)

1. a solid state heat compression low-temperature bonding method that uses nickel micropin awl is characterized in that, comprises that step is following:

1), select to have mutual coupling the electrical interconnection pad treat key;

2), on a wherein face down bonding dish of treating the bonding idol, form surface portion by soft first metal, the projection that the bottom is made up of second metal;

3), preparation nickel micropin awl layer on the pad of the opposite side of treating the bonding idol;

4), engage and to treat key, comprise treating that bonding idol surface pads aims at, make that mate in each nickel micropin awl zone on a plurality of projections that have a soft alloy and the opposite side surface; And be heated to first temperature to contact area, and make contact both sides to accomplish the electrical interconnection bonding of welding disking area.

2. the solid state heat compression low-temperature bonding method of use nickel micropin awl as claimed in claim 1; It is characterized in that; Wherein the preparation of nickel micropin awl film can realize through electrodeposition process; Comprise the electro-deposition parameter of time, current density, additive concentration through control, control pin cone height is not waited to 2000 nanometers by 200 nanometers.

3. the solid state heat compression low-temperature bonding method of use nickel micropin awl as claimed in claim 2; It is characterized in that; Behind the preparation nickel micropin awl film, at the surface preparation antioxidation coating, antioxidation coating is an oxidation resistant metal or alloy under the high temperature; Thickness is about several nanometers to tens nanometer, and does not change the surface topography of pin awl.

4. as the sharp solid state heat compression low-temperature bonding method that requires 1 described use nickel micropin awl, it is characterized in that, treat wherein that contacting with each other of key also comprises to apply bonding pressure.

5. the solid state heat compression low-temperature bonding method of use nickel micropin awl as claimed in claim 4; It is characterized in that; Wherein bonding pressure need keep the several seconds by several minutes during first temperature; Release key resultant pressure then, the optimize results decision that the retention time is required by solder metal kind, temperature, bonding pressure.

6. the solid state heat compression low-temperature bonding method of use nickel micropin awl as claimed in claim 1 is characterized in that second metal of its bumps lower floor is through the electrodeposition process preparation.

7. the solid state heat compression low-temperature bonding method of use nickel micropin awl as claimed in claim 1 is characterized in that wherein first metal cap of bump surface has than low melting point, prepares through electrodeposition process.

8. the solid state heat compression low-temperature bonding method of use nickel micropin awl as claimed in claim 1; It is characterized in that; Wherein being heated to first temperature can be through contact or contactless mode of heating; First temperature is no more than the fusing point of first metal and solder metal, the optimize results decision that first temperature is required by first metal species and bonding pressure.

9. the solid state heat compression low-temperature bonding method of use nickel micropin awl as claimed in claim 2 is characterized in that the said method of treating that key engages is:

To treat that the bonding idol is positioned over respectively in hot compression connector first and second fixtures; Keep temperature to be lower than first temperature; Through first or second fixture one or both of moving each other; Make a plurality of soft alloy projections of a side and opposite side surface preparation have the pad metal piece of micropin awl to contact with each other, make temperature reach first temperature fast and keep, exert pressure between first and second fixtures simultaneously and keep through heater; Realize bonding until the contact point place, take off the element that bonding is accomplished from connector;

Under second temperature, through after a while tHeat treatment, improve to engage performance.

10. the solid state heat compression low-temperature bonding method of use nickel micropin awl as claimed in claim 9 is characterized in that wherein temperature and contact pressure keep the several seconds by several minutes, is the optimize results decision by first metal species, temperature, pressure requirement.

11. the solid state heat compression low-temperature bonding method of use nickel micropin awl as claimed in claim 9 is characterized in that wherein second temperature is by first metal species and retention time tOptimize results decision.