TWI360211B - Wafer-level interconnect for high mechanical relia - Google Patents

Description

1360211 IX. DESCRIPTION OF THE INVENTION: TECHNICAL FIELD The present disclosure relates generally to structures and methods for semiconductor devices, and more particularly to electronic wafer level wafer size packages and flip chip packages and assemblies. Structure and method. [Prior Art]

The electronics packaging industry has long had a desire to improve the mechanical performance of lead-free (Pb) solders for wafer-level wafer size packaging and flip chip components. Previous efforts have included minor additions or doping with various elements such as cobalt and zinc. Previous efforts have also included the study of the effects of doping (eg, doping titanium, iron, cobalt, platinum, indium, and nickel) on the mechanical properties of lead-free solders.

One of the problems observed with existing interconnected structures is the failure of early interconnect structures from individual, combined or a series of mechanical damage events, such as drop shock, shock, and shear. Previous attempts to solve this problem and increase the mechanical strength of the joint include the use of Young's m 〇du 1 us and lower hardness solder to aid in reducing the fragile interior by making the solder more flexible. The wiring structure is broken (for example, indium-based lead-free solder, tin-copper-free solder, or tin-silver-copper alloy with less silver content). These prior art attempts have not satisfactorily removed early interconnect failures. Accordingly, it is desirable to have improved joint mechanical strength when using solder to fabricate wafer level wafer scale packages or flip chip components. SUMMARY OF THE INVENTION 5 1360211 The structure described herein includes an interconnect structure disposed between spaced electrical contacts. The interconnect structure contains a lead-free (Pb) tantalum alloy consisting essentially of nickel (Ni), tin (sn), silver (Ag), and copper (Cu). The nickel (Ni) in the lead-free (Pb) solder alloy is in the range of 0.01 to 0.20 by weight (wt%).

An embodiment of the structure described herein is an element comprising a substrate, a first metal layer disposed on the substrate, a solder block body disposed on the metal layer, and a body of the solder block A wafer element coupled to the metal layer. The solder block main system is composed of nickel (Ni), tin (Sn), silver (Ag), and steel (Cu). Nickel (Ni) is in the range of weight percent (wt%) 〇.〇l to 0.20. [Embodiment] The following description and drawings illustrate specific embodiments of the systems and methods described herein. Other embodiments may include structural, logical, process, and other changes. The examples represent only possible variations.

Elements that perform various embodiments of the present structures and methods are described below. Many components can be configured with well-known structures. It should also be understood that the techniques of the present structures and methods can be performed using a variety of techniques. The present invention generally relates to an improved interconnect structure using a solder alloy containing a relatively low proportion of nickel. The improved structure typically provides, for example, a lead-free solder for wafer-scale package (CSP) or flip-chip interconnect structure with improved joint mechanical strength and long-term mechanical reliability. In one embodiment, a nickel assisted lead-free solder alloy having a weight percentage (wt ° / 〇) of 0. 〇 1 to 20 . 20 is used. For example, the lead-free solder alloy preferably consists essentially of tin-silver-copper and 0.01 to 60.20 wt% nickel. Tin, silver, and copper can generally be used in a conventional ratio. The solder alloy may, for example, be reflowed and attached to an under bump metal (which may be formed, for example, as a vacuum deposited film or a plated film). Other conventional manufacturing techniques can be used to make the inner structure as described below. The combination of a salt-free nickel-assisted lead-free alloy and an under-bump-metallurgy (UBM) generally provides improved joint mechanical strength by controlling the solder/UBM interface and tin grain boundaries within the solder block (internal The metal structure of the dendritic structure. This was confirmed by the inventors in the improved high-speed shear state and confirmed by the drop test results, compared to the same structure using a nickel-free lead-free alloy. This joint strength improvement is for the use of wafer level CSP or overlay. It is advantageous to have an electronic component of a crystal interconnect structure in which the component is susceptible to falling, particularly mobile objects such as mobile phones, personal digital assistants, Mp3 players, game consoles and the like. A more specific embodiment of the structure in which the nickel auxiliary solder alloy interconnect structure can be performed will now be discussed in more detail later. In the first embodiment, the solder is used to form an interconnect structure between two different substrates. The interconnect structure typically comprises a solder block composition' and an intermetallic compound (IMC) at the solder block and a metal structure (e.g., UBM) interface on the wafer. The IMC is formed between the solder and the UBM using a metallurgical reaction. UBM is usually classified as a film or a thick film. The film UBM is typically formed by vacuum deposition (e.g., splash deposition or steam forging). The thick film UBM is usually formed by a bond using the 1360211. An example of a suitable UBM structure is steel contact with the name of the welding company. Other possible options include, but are not limited to: the following alloys: Chin / Record / Feed, Chin / Record / Copper, Titanium / Steel Chin Town / Record / Copper, Chin Town / Nickel Vanadium / Copper, Chromium / Nickel / Copper Or chrome / nickel / copper. A composite thick film t-type can be formed using the following alloys: copper-phosphorus/gold, nickel-phosphorus/nickel-palladium/gold, palladium-phosphorus/gold, palladium-phosphorus, nickel/gold or steel/nickel/gold. The joint strength of the interconnect structure depends on the ductility (flexibility) of the solder block and the joint mechanical strength of the IMC at the solder/UBM interface. Although the interconnect structure is expected to have enhanced reliability, the interface imc itself is considered to be quite fragile. Improved joint mechanical performance of the lead-free solder interconnect structure can be assisted by: - or a combination of: improving the microstructure of the solder block, improving the compatibility of the structure (eg, stress level or solubility of the coffee film) And by improving control over the growth and development of the interface IMC. Using the known tempering shear and high-speed cold-drawn ball test ((iv) ρ-υ to simulate a mechanical drop impact event observed using the above-mentioned zen alloy within the wafer level and the overlay internal structure Improvements in the structure of the solder block. This is a test that uses a wide range of test conditions (eg, impact shear, w force pull and impact shear height) to Estimate the use of nickel-assisted solder. Using the known drop test equipment y, he tested the drop test reliability of the structure made of Jin-assisted solder, which is better than the available 妯S妯, he The choice is much better. The test also includes a compatibility test with a variety of 8 1360211 for the total film thickness of the γ UBM selected film and the thickness of the soluble metal. The first test shows the assembly before the substrate is assembled. A wafer-level wafer size or a cross-sectional view of a portion of a flip chip package 100. A wafer component 1〇2 (eg, a typical build-up circuit (1C) die) is provided for subsequent connection to the substrate (see section 2). Figure). A UBM 108, formed on wafer component 1 02, contact with solder bumps 106 (eg, solder bumps or solder balls) at interface mc 114. In actual packages, a large number of solder bumps or solder balls are typically used. Figure 2 shows the assembly A cross-sectional view of a portion of the solder interconnect structure 2. The wafer element 1〇2 is bonded to a substrate 104 (eg, a printed circuit board) by a solder block 106. A conventional metal surface treatment is formed on the substrate 104. Or layer n〇, which is conductive to solder adhesions and is in contact with solder bumps 1〇6 at interface IMC 112. Solder block 106 possesses the solder alloy composition described herein. Metal surface treatment 110 may 'for example, It has a copper upper layer similar to UBM. "But it is not always the case. If the metal surface treatment has a copper surface treatment, the thickness is usually significantly larger than the UBM on the wafer side. The copper surface treatment on the substrate 104 can be, For example, about 2 to 5 micrometers (pms). Various substrate 104 surface treatments can be used. For example, a common substrate surface treatment is copper on the surface along with the organic layer to protect the steel from oxidation 'called' Copper OSP''. Other Examples are nickel phosphorus/gold, or silver (sometimes referred to as immersion silver plating). The thickness of the interface IM C 1 1 4 can be, for example, less than about 2 〇 micrometers (pms). The thickness of the UBM 108 can be, for example, The thickness below about 2. pm (βs) β can vary greatly in other embodiments. 9 1360211

The interconnect structures and methods described herein can be implemented, for example, in other types of wafer size or wafer level packages (eg, on-chip-on-board (COB') component applications or Standard flip chip package for flip chip packaging applications. Examples of such implementations are disclosed in U.S. Patent No. 6,441,487 (issued to Alenius et al. on August 27, 2002, entitled to the use of high-stretch solder ball wafer size packages) and US patents. No. 5,844,304 (issued to Kata et al. on December 1, 1998, entitled Process for Manufacturing Semiconductor Components and Semiconductor Wafers), and U.S. Patent No. 5,547,740 (Approved to Higdon et al., August 20, 1996, titled The solderable contact of the crystallographic circuit component is described in U.S. Patent No. 6,251,501 (issued to Higdon et al., entitled: Surface Mounting Circuit Components and Solder Bump Methods, June 26, 2001), each of which is incorporated herein by reference. This is incorporated herein by reference in its entirety to the teachings of the application, structure, and method of manufacture.

The interconnect structure itself is now discussed in more detail in a specific example. In one embodiment, a lead-free solder alloy consists essentially of tin-silver-steel and 〇.〇1 to 〇20 wt% nickel. An example of this lead-free solder alloy is 98.4% tin 1·0/ό silver-0.5% copper-0.1%. As an example of the composition of the tin-silver-copper composition, the silver component may be about 0.25 to 4.0 wt〇/〇, and the copper may be about 2.0 wt0/〇. The tin component can be, for example, from about 99.75 to 94.5 wt%, or provide a balance of any of the ingredients listed above. As in any solder composition, there are typically trace elements present which are not critical and are not expected to affect the properties of the interconnected structure while remaining within conventional standards. The solder alloy can be, for example, a discontinuous solder sphere (i.e., solder ball) or a solder paste type. The solder can, for example, be reflowed to a UBM formed by vacuum deposition of a thin crucible or a plated film. 10 The above solder alloy composition, together with the application of UBM, provides a smoother, thicker thickness at the UBM/solder interface that minimizes the heterogeneous growth of this fragile interface. In the example, the upper layer of the UB is copper, and the solder block is, in a preferred embodiment, the UBM upper surface steel is formed as a metal intermetallic (IMC) layer during the reflow process, in the UBM. The boundary layer. Conversely, if the UBM is only a copper layer, it will never be at any point or interface in the process. In addition, the use of the above structure can surround the internal branches of the tin grain boundary within the solder reflow block. Weld a low degree of intermetallic. This assists in making the solder block more flexible than unrecorded. In one embodiment, the UBM structure has a shoulder because of the film requirements required by certain packaging industries. This is in contrast to electro-forged copper only, which does not conform to the UBM fabrication seal. U B in the preferred embodiment. Other thin film metal layers should be used in the UBM upper layer to form the IMC. For example, the minimum thickness of the copper layer in the UBM should be such that in the preferred embodiment, the smoothing of the IMC layer in the copper and solder in the UBM can also contribute to the formation of the IMC. In other embodiments, the different metals in the UBM react with the solder and form the IMC and its properties, such as by reacting nickel tin in the UBM in a nickel-phosphorus-based UBM instead of copper. Smooth IMC layer. It can assist in the better implementation of the reaction of thinner metal. It is clear that most of this reveals that this rather thick skin is completely consumed. A limited amount of copper is then provided in the solder zone to limit the amount of copper used in a thin layer. For example, nickel sharp β is expected to be about 7,000 angstroms. The nickel reacts. To some extent, the structural combination contributes. Example 1360211 in the solder Within the expected nickel doping range described herein, it was observed that the interface IMC thickness was thicker than the same nickel-free doped alloy. It is further observed that the smoother microstructure of the interface IMC is more satisfactory than the zigzag, scalloped microstructures prevalent in lead-free alloys without nickel. This smoother microstructure allows for an average stress within the IMC. The jagged, ruffled microstructure has a region of higher stress because the structure is not as homogeneous as a smoother microstructure.

For example, Figure 3 shows a nickel-free doped interface IMC configuration 300. Configuration 300 shows a glitch 3 02 that is unpleasant. Conversely, Fig. 4 shows the configuration of the interface IMC 1 14 having the nickel doping as described above. The surface 400 of the interface IMC 114 is substantially smooth compared to the nickel-free doped IMC. Regarding the fabrication of the interconnect structure itself, conventional wafer level wafer size and flip chip process can be used. For example, solder can be applied to the UBM and solder reflow to achieve a dazzle to form a solid weld between the solder and the UB.

In another embodiment, a thick film copper UBM can be used. Nickel in the solder reacts with copper during the reflow process to form a smooth interface IMC 1 14 layer (see Figure 2). Improved interconnect structures and methods have been described by the foregoing disclosure. The above structures and methods generally provide the advantage of mechanical integrity through the use of nickel-doped tin-silver-copper alloy solders, the flexibility of the solder block and the heterogeneous growth and formation of the interface IMC thickness, It is the most vulnerable structure in the interconnected structure and both are improved. The overall structure is significantly more ductile than other available options, increasing the ability of the structure to absorb destructive mechanical energy from, for example, the impact of 12 1360211 drop shock, shock and shear. The above description of the specific embodiments fully discloses the general principles of the disclosure, and others can be easily modified and/or changed by applying the present knowledge and used in various applications without departing from the basic concepts. Therefore, such changes or modifications are within the meaning and range of equivalents of the disclosed embodiments. The words and terms used herein are for the purpose of description and not limitation.

BRIEF DESCRIPTION OF THE DRAWINGS For a fuller understanding of the present disclosure, reference is now made to the drawings, in which like reference A cross-sectional view of a wafer level wafer size or a portion of a flip chip package before assembly to a substrate. Figure 2 illustrates an assembled solder interconnect structure in accordance with an illustrative embodiment of the present disclosure. Figure 3 shows the interface of the nickel-free doped interface IMC (intermetallic compound).

Figure 4 illustrates a nickel-doped interface IMC configuration in accordance with an illustrative embodiment of the present disclosure. The examples presented herein are illustrative of specific embodiments and are not to be considered as limiting the invention in any way. [Main component symbol description] 100 Package 102 Wafer component 104 Substrate 106 Solder block 13 1360211 108 UBM 110 Metal surface treatment 112, 114 Interface IMC 200 Solder interconnect structure 300 Configuration 302 Surge 400 Surface

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Claims (1)

1360211 第丨 (8) 丨竹年1丨月卫Application Patent Range 1. An internal structure, disposed between two spaced electrical contacts, etc. Electrical contacts including a first metal contact and a second Metal contacts, each of which is on a different substrate, the interconnect structure comprising: a lead-free (Pb) solder alloy comprising nickel (Ni) and tin (Sn), the nickel (Ni) Between 0.01 and 0-20 in weight percent (wt%); an intermatal compound (ICC) layer having a top surface and a bottom surface, the top surface being in contact with the solder alloy, and the bottom surface In contact with the first metal contact, the IMC layer comprises a copper and a recorded compound. 2. The interconnect structure of claim 2, wherein the interconnect structure is included in a flip chip package. 3. The interconnect structure of claim i, wherein the first metal contact comprises a record. 4. The interconnect structure of claim 1, wherein the solder consists essentially of nickel (tin), tin (Sn), silver (Ag), and copper. 5. The interconnect structure of claim 1, wherein the individual substrate of the first metal contact is a semiconductor die, the semiconductor die & The second metal contact is electrically coupled. The internal structure of claim 1, wherein the first metal contact comprises a top layer comprising copper. 7. The interconnect structure of claim 6 wherein the first metal contact further comprises an intermediate layer below the top layer and the intermediate layer comprises nickel. 8. The interconnect structure of claim 1, wherein the copper and nickel compound promotes smoothing of the top surface of the IMC layer. 9. An interconnect structure comprising: a semiconductor substrate comprising an integrated circuit; an under-bump-metallurgy (UBM) on the substrate, the .UBM comprising nickel And the integrated circuit is electrically coupled to the UBM; an intermetallic compound (IMC) layer is disposed on the UBM, the IMC layer comprises a compound of copper and nickel; and a solder block body is disposed on the IMC layer The solder bulk body comprises nickel (Ni), tin (Sn), silver (Ag), and copper (Cu), wherein the nickel (Ni) is in the range of 0.01 to 0.20 by weight (wt%). 10. The component of claim 9, wherein the solder block body comprises: 16 1360211 weight percent (Wt%) greater than about 94.5 tin (Sη); weight percent (wt%) less than about 4.0 Silver (Ag); copper (Cu) having a weight percentage (wt%) of less than about 2.0; and nickel (Ni) having a weight percentage (wt%) of less than about 0.1. 11. The interconnect structure of claim 9, wherein the solder block body comprises: a weight percentage (wt%) of about 0.25 to 4.0 silver (Ag); and a weight percentage (wt%) lower than About 2.0 copper (Cu). 1. The interconnect structure of claim 9, wherein the under-metal layer (UBM) is a film having a top layer of copper and a recorded underlying layer. 1. The interconnect structure of claim 9, wherein the IMC layer has a thickness that is less than about 2.0 microns. 1. The interconnect structure of claim 9, wherein the sub-ball metal layer (UBM) is a film composed of one or more alloys selected from the group consisting of the following: Each consists of: aluminum (A1) - nickel vanadium (NiV) - copper (Cu); titanium (Ti) - nickel vanadium (NiV) - copper (Cu); titanium (Ti) - nickel (Ni) - copper (Cu Titanium tungsten (TiW) - copper (Cu); 17 1360211 titanium tungsten (TiW) - nickel (Ni) - copper (Cu); titanium tungsten (TiW) - nickel vanadium (NiV) - copper (Cu); Cr)-nickel (Ni)-copper (Cu); and chromium (<: 〇-nickel-vanadium (1^¥)-copper ((:11). 15. Interconnected as described in claim 9 a structure wherein the UBM has a structure selected from the group consisting of: (i) aluminum (A1)-nickel vanadium (NiV)-copper (Cu); and (ii) titanium (Ti)-nickel hunger ( NiV)-copper (Cu). 1. 6. An interconnect structure located between two spaced apart electrical contacts, the interconnect structure comprising: a lead-free (Pb) solder alloy that passes An interfacial intermetallic compound (IMC) layer in a sub-metal layer (UBM) is reflowed and attached to a copper-containing under-ball metal on a top surface, under the ball a metal is disposed between the two contacts, and the lead-free (Pb) solder alloy comprises nickel (Ni), tin (Sn), silver (Ag), and copper (Cu); wherein the nickel (Ni) content is The weight percentage (wt%) is in the range of 0.01 to 0.20; and wherein the IMC layer comprises a compound of copper and nickel.