Cu-Sn series welding flux for high-reliability welding joint and preparation method of Cu-Sn series welding flux

Abstract

The invention belongs to the technical field of new materials, and discloses a Cu-Sn series solder for a high-reliability welding head and a preparation method of the Cu-Sn series solder. The preparation method comprises the following steps: carrying out polishing, cleaning and glow sputtering cleaning treatment on a base material to obtain a clean base material; under argon, sputtering a copper target by adopting a magnetron sputtering technology, and depositing a pure copper layer on the surface of the clean base material; simultaneously sputtering a copper target and a tin target so as to deposit a copper-tin co-sputtering layer on the surface of the pure copper layer; sputtering a tin target to deposit a pure tin layer on the surface of the copper-tin co-sputtering layer to obtain a Cu-Sn series solder with a multi-layer structure; and in the copper-tin co-sputtering layer, the atomic ratio of Cu to Sn is (5-9): 1. The preparation method is simple and free of pollution in the whole process, the cost is saved, and the use efficiency is improved; and the prepared Cu-Sn series welding flux can effectively reduce the Cu-Sn mutual diffusion distance in the transient liquid phase welding process, holes are reduced, welding is more sufficient, and the reliability of a welding joint is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of new materials, and in particular to a Cu-Sn solder for a high-reliability welding head and a preparation method thereof. Background Art

[0002] Compared with the first and second generation semiconductor materials, the third generation semiconductor materials have a wider bandgap, higher breakdown electric field, higher thermal conductivity, higher electron saturation rate and higher radiation resistance. They are more suitable for making high temperature, high frequency, high power and radiation-resistant devices. They can be widely used in high voltage, high frequency, high temperature and high reliability fields, including radio frequency communications, radars, satellites, power management, automotive electronics, industrial power electronics, etc.

[0003] With the widespread application of third-generation semiconductor materials, not only are package solder joints required to have lower sizes, but they are also required to have better heat dissipation performance and high-temperature reliability. Transient liquid phase welding technology can effectively reduce the bonding temperature and bonding time, and the intermetallic compound solder joints obtained after bonding have high service temperatures and excellent thermodynamic properties. Therefore, transient liquid phase welding technology is one of the most promising interconnect technologies.

[0004] Cu-Sn solder has excellent electrical and thermal conductivity, low reactivity, low price and easy to obtain, and is the most cost-effective advanced transient liquid phase welding packaging solder. The intermetallic compounds formed by Cu-Sn solder after transient liquid phase welding mainly include Cu6Sn5 phase and Cu3Sn phase. Excessive Cu6Sn5 phase in the weld will reduce the thermal fatigue life, tensile strength, fracture toughness and isothermal shear fatigue life of the solder joint, while the Cu3Sn phase has better Young's modulus, fracture toughness and melting point, higher conductivity and shear strength. Therefore, a single Cu3Sn phase is an important guarantee for obtaining high-strength and high-reliability welded joints.

[0005] At present, traditional Cu-Sn solders are mostly prepared by electroplating. However, it is difficult to accurately control the composition and thickness ratio of Cu-Sn solders by electroplating, and it is impossible to obtain a single Cu3Sn phase intermetallic compound. The prepared Cu-Sn solders have a long subsequent bonding time, and there are holes in the weld, which can easily lead to the initiation of cracks in the weld area and reduce its strength. Summary of the invention

[0006] In order to solve the above technical problems, the present invention provides a Cu-Sn solder for high-reliability welding joints and a preparation method thereof. The present invention proposes to prepare the Cu-Sn solder by magnetron sputtering technology from the perspective of controlling the types of Cu-Sn intermetallic compounds, and it is easy to control the element ratio of the solder layer by co-sputtering deposition and generate a Cu3Sn phase after bonding. The solder composition and thickness ratio of the Cu-Sn solder can be accurately controlled, and the holes in the weld area can be effectively reduced, and the reliability of the welding joint can be improved. The method is simple and easy to commercialize.

[0007] The Cu-Sn solder for a high reliability welding head and the preparation method thereof of the present invention are realized by the following technical scheme:

[0008] The first object of the present invention is to provide a method for preparing a Cu-Sn solder for a high reliability solder joint, comprising the following steps:

[0009] Step 1, pretreatment of the substrate: polishing and then cleaning the substrate to obtain a pretreated substrate.

[0010] It should be noted that the present invention does not limit the type of substrate, as long as it can meet the requirements of electronic packaging. For example, 6061 aluminum alloy, a commonly used metal for packaging, can be used.

[0011] The present invention takes into account that there may be impurities such as oil stains and surface defects on the substrate surface, so it is first polished and then cleaned to remove impurities on the substrate surface and improve its surface roughness, so as to improve the quality of subsequent Cu-Sn solder formation.

[0012] It should also be noted that since the subsequent glow sputtering cleaning treatment and the magnetron sputtering process in each step are carried out in the magnetron sputtering equipment, the present invention installs the pretreated substrate on the workpiece turntable in the vacuum chamber of the magnetron sputtering equipment, and places the pure copper target and the pure tin target on the target position in the magnetron sputtering vacuum chamber, respectively, to facilitate the subsequent glow sputtering cleaning treatment and the deposition of the pure copper layer, the copper-tin co-sputtering layer and the pure tin layer.

[0013] Step 2, glow sputtering cleaning treatment: performing glow sputtering cleaning treatment on the pretreated substrate to obtain a clean substrate.

[0014] It should be noted that the present invention takes into account that adsorbents and oxide layers may still exist on the surface of the pretreated substrate, which may affect the subsequent film-based bonding strength of the Cu-Sn solder and the substrate, so the pretreated substrate is further subjected to glow sputtering cleaning treatment.

[0015] Step 3, depositing a pure copper layer: in an argon atmosphere, magnetron sputtering technology is used, with a copper target as a sputtering target material, to deposit a pure copper layer on the surface of the clean substrate.

[0016] It should be noted that the present invention takes into account the factors such as high purity, good density and good uniformity of the thin film prepared by magnetron sputtering technology, and therefore adopts magnetron sputtering technology to deposit a layer of pure copper on the surface of the substrate to achieve better connection between the Cu-Sn solder and the substrate through the pure copper layer.

[0017] Step 4, depositing a copper-tin co-sputtering layer: using a copper target and a tin target as co-sputtering target materials, depositing on the surface of the pure copper layer at the same time, so as to deposit a copper-tin co-sputtering layer on the surface of the pure copper layer.

[0018] It should be noted that the present invention adopts magnetron sputtering technology, with copper target and tin target as co-sputtering target materials, so that the copper sputtered by the copper target and the tin sputtered by the tin target can form a copper-tin co-sputtering layer during the sputtering process. The present invention can adjust the composition ratio of copper and tin in the formed copper-tin co-sputtering layer by adjusting the process parameters of magnetron sputtering, so that a single Cu3Sn phase can be obtained by adjusting the composition ratio, so that the Cu-Sn solder finally obtained by the present invention has high strength and high reliability. At the same time, the preparation using magnetron sputtering technology can reduce the diffusion reaction distance of copper and tin during subsequent heat treatment, solve the hole problem caused by long-distance mutual diffusion of copper and tin, and further improve the high strength and high reliability of the Cu-Sn solder finally obtained by the present invention.

[0019] It should also be noted that the present invention can adjust the atomic ratio of Cu and Sn in the copper-tin co-sputtered layer by regulating the sputtering power of the copper target and the tin target during the magnetron sputtering process. By adjusting the atomic ratio of Cu and Sn in the copper-tin co-sputtered layer to 5 to 9:1, it is ensured that the copper-tin component ratio in the formed copper-tin co-sputtered layer is controllable, thereby avoiding the problem of failure to form a full Cu3Sn phase due to an excessively high or low copper-tin component ratio, and ensuring that the Cu-Sn solder finally obtained by the present invention can obtain a single Cu3Sn phase.

[0020] In some preferred embodiments of the present invention, when the atomic ratio of Cu to Sn is 6.5:1, the overall atomic ratio of Cu to Sn in the Cu-Sn solder is 3:1, which is easy to bond in subsequent heat treatment to form a Cu3Sn phase.

[0021] Step 5, depositing a pure tin layer: using a tin target as a sputtering target, depositing a pure tin layer on the surface of the copper-tin co-sputtering layer to form a Cu-Sn solder with a multi-layer structure composed of a pure copper layer, a copper-tin co-sputtering layer and a pure tin layer on the surface of the substrate.

[0022] It should be noted that the present invention takes into account the factor that the low-melting-point tin layer needs to melt and diffuse with the solid copper-tin co-sputtered layer in the subsequent bonding process, and further deposits a pure tin layer on the surface of the copper-tin co-sputtered layer, so that the pure tin layer melts at low temperature and diffuses with the solid copper-tin co-sputtered layer at low temperature, and the connection is achieved by cooling and solidifying.

[0023] It should also be noted that the present invention takes into account that the traditional Cu-Sn solder is composed of two layers of pure copper layer and pure tin layer, and the prior art needs to melt the pure tin layer at low temperature when compounding the pure copper layer and the pure tin layer, and then make it undergo solid-liquid interdiffusion with the high melting point solid phase copper to generate intermetallic compounds, and realize connection after solidification. However, the subsequent bonding time of the Cu-Sn solder prepared by the above method is relatively long, and there are holes in the weld, which easily leads to the initiation of cracks in the weld area and reduces its strength. Compared with the traditional Cu-Sn solder, the present invention adds a copper-tin co-sputtering layer between the pure copper layer and the pure tin layer, that is, by sequentially depositing a pure copper layer, a copper-tin co-sputtering layer and a pure tin layer on the surface of the substrate, a Cu-Sn solder with a multilayer structure compounded by a pure copper layer, a copper-tin co-sputtering layer and a pure tin layer is formed, thereby reducing the diffusion distance of liquid Sn and solid Cu during subsequent heat treatment, and solving the hole problem caused by the long-distance interdiffusion of copper and tin.

[0024] In some preferred embodiments of the present invention, in the Cu-Sn solder, the atomic ratio of Cu to Sn is 3.36:1-2.36, so as to adjust the copper-tin ratio and control the formation of a single Cu3Sn phase after subsequent heat treatment.

[0025] In some preferred embodiments of the present invention, when depositing the copper-tin co-sputtering layer, argon gas is introduced, the argon gas flow rate is adjusted to 15sccm~25sccm, and the working gas pressure is controlled to be 0.1Pa~1Pa; and during sputtering deposition, the sputtering power of the copper target is controlled to be 100W~150W, the sputtering power of the tin target is controlled to be 65W~100W, and the deposition time is 110min~147min.

[0026] In some preferred embodiments of the present invention, when depositing the pure copper layer, argon gas is introduced to control the working gas pressure to be 0.1Pa~1Pa; and during sputtering deposition, the sputtering power of the copper target is controlled to be 140W~160W, and the deposition time is 40min~60min.

[0027] In some preferred embodiments of the present invention, when depositing the pure tin layer, argon gas is introduced to control the working gas pressure to be 0.1Pa-1Pa; and during sputtering deposition, the sputtering power of the tin target is controlled to be 70W-90W, and the deposition time is 40min-60min.

[0028] In some preferred embodiments of the present invention, the glow sputtering cleaning process is carried out by the following steps: evacuating to a background vacuum degree of ≤0.005Pa, introducing argon gas, adjusting the argon gas flow rate to 15sccm~25sccm, and controlling the working gas pressure to 0.4Pa~1.6Pa; applying a bias voltage of -500V~-200V to the substrate, and the glow sputtering cleaning time is 10min~20min.

[0029] In some preferred embodiments of the present invention, the polishing is carried out by the following steps: polishing with 400#, 600#, 1000#, 1200#, 1500#, 2000#, 3000# and 4000# SiC water abrasive paper, and finally polishing to a mirror surface with a diamond spray polishing agent with a particle size of 1.5μm and 0.5μm, respectively.

[0030] The second object of the present invention is to provide a Cu-Sn solder prepared by the above preparation method, wherein the Cu-Sn solder has a composite structure of a pure copper layer, a copper-tin co-sputtered layer and a pure tin layer from the inside to the outside on the surface of the substrate.

[0031] In some preferred embodiments of the present invention, the thickness of the pure copper layer is 0.8 μm to 1.2 μm.

[0032] In some preferred embodiments of the present invention, the thickness of the pure tin layer is 0.6 μm to 1 μm.

[0033] In some preferred embodiments of the present invention, the thickness of the copper-tin co-sputtered layer is 2 μm to 4 μm.

[0034] Compared with the prior art, the present invention has the following beneficial effects:

[0035] The present invention starts from the perspective of controlling the types of Cu-Sn intermetallic compounds, utilizes magnetron sputtering technology, and sequentially deposits a pure copper layer, a copper-tin co-sputtering layer, and a pure tin layer on the surface of a substrate, forming a Cu-Sn solder having a multilayer structure composed of a pure copper layer, a copper-tin co-sputtering layer, and a pure tin layer, so as to reduce the diffusion distance of liquid Sn and solid Cu during subsequent heat treatment by adding a copper-tin co-sputtering layer between the pure copper layer and the pure tin layer, and solves the hole problem caused by the long-distance mutual diffusion of copper and tin. In addition, the present invention can regulate the element ratio of the solder layer by co-sputtering deposition and generate a Cu3Sn phase after bonding, can accurately control the solder composition and thickness ratio of the Cu-Sn solder, can effectively reduce the holes in the weld zone, improve the reliability of the welding joint, and the method is simple and easy to commercialize.

[0036] The preparation method of the present invention is simple and pollution-free throughout the process, thus saving costs and improving utilization efficiency; and the copper-tin component ratio of the prepared Cu-Sn solder is controllable, which can effectively reduce the Cu-Sn mutual diffusion distance during transient liquid phase welding, reduce the generation of holes, make welding more complete, and improve the reliability of the welding joint.

[0037] The Cu-Sn solder prepared by the present invention has good crystallinity, high film density and uniformity. The test results show that after the Cu-Sn solder of the present invention is welded, there are no holes on the bonding interface, the bonding strength is high, and the welding effect is good. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 The schematic diagram of the structure of the Cu-Sn solder prepared by the present invention; in the figure, 1 is a substrate, 2 is a pure copper layer, 3 is a copper-tin co-sputtering layer, and 4 is a pure tin layer.

[0039] Figure 2 This is a cross-sectional scanning electron microscope image of the Cu-Sn solder prepared in Example 1. DETAILED DESCRIPTION

[0040] The technical solutions in the embodiments of the present invention will be described clearly and completely below.

[0041] Example 1

[0042] This embodiment provides a Cu-Sn solder for a high reliability solder joint, and the Cu-Sn solder is prepared by the following steps:

[0043] Step 1, pretreatment of substrate:

[0044] 1.1) In this embodiment, 6061 aluminum alloy is used as the substrate, and it is polished with 400#, 600#, 1000#, 1200#, 1500#, 2000#, 3000# and 4000# SiC water abrasive paper, and finally polished to a mirror surface with a diamond spray polishing agent with a particle size of 1.5μm and 0.5μm, respectively, to obtain a polished 6061 aluminum alloy.

[0045] 1.2) The polished 6061 aluminum alloy was ultrasonically cleaned in acetone, alcohol and deionized water for 20 minutes, and then dried to obtain the pretreated 6061 aluminum alloy.

[0046] Step 2, glow sputtering cleaning process:

[0047] 2.1) The pretreated 6061 aluminum alloy was fixed on a sample plate and then mounted on a workpiece turntable in a vacuum chamber of a magnetron sputtering device, and a pure copper target and a pure tin target were placed on target positions in the vacuum chamber of the magnetron sputtering device, respectively.

[0048] 2.2) After the vacuum degree of the sputtering chamber of the magnetron sputtering equipment is evacuated to 0.005Pa, argon gas is introduced and its flow rate is adjusted to 20sccm, the pressure in the sputtering chamber is controlled to be 0.5Pa, the bias power supply is turned on and the power is adjusted to -200W, and glow cleaning is performed for 20min to obtain a clean 6061 aluminum alloy.

[0049] Step 3, depositing a pure copper layer:

[0050] Argon gas was introduced into the vacuum chamber and its flow rate was adjusted to 20 sccm. The working gas pressure was controlled to 0.5 Pa. The power was turned on to sputter the copper target. The sputtering power was adjusted to 150 W and the sputtering time was 50 min. A 1 μm thick pure copper layer was formed on the clean 6061 aluminum alloy surface.

[0051] Step 4, depositing the copper-tin co-sputtered layer:

[0052] Argon gas was introduced into the vacuum chamber and its flow rate was adjusted to 20 sccm, the working gas pressure was controlled to 0.5 Pa, and the power supplies for controlling the copper target and the tin target were turned on at the same time. The sputtering power of the copper target was adjusted to 150 W, and the sputtering power of the tin target was adjusted to 100 W, so that the copper target and the tin target were deposited on the surface of the pure copper layer at the same time. The sputtering time was 110 min, so as to deposit a copper-tin co-sputtering layer with a thickness of 3 μm on the surface of the pure copper layer, and the atomic ratio of Cu and Sn in the copper-tin co-sputtering layer formed in this embodiment was 5:1.

[0053] Step 5, depositing a pure tin layer:

[0054] Argon gas was introduced into the vacuum chamber and its flow rate was adjusted to 20 sccm, the working gas pressure was controlled to 0.5 Pa, the power was turned on to sputter the tin target, the sputtering power was adjusted to 80 W, and the sputtering time was 50 min to deposit a pure tin layer with a thickness of 800 nm on the surface of the copper-tin co-sputtered layer.

[0055] After the coating is completed, the ventilation is stopped and the vacuum state is maintained. After the furnace is cooled to room temperature, the sample is taken out, and a Cu-Sn solder having a multilayer structure composed of a pure copper layer 2, a copper-tin co-sputtered layer 3 and a pure tin layer 4 is obtained on the surface of the substrate 1. The schematic diagram of the structure is shown in FIG. Figure 1 shown.

[0056] Example 2

[0057] This embodiment provides a Cu-Sn solder for a high reliability solder joint, and the Cu-Sn solder is prepared by the following steps:

[0058] Step 1, pretreatment of substrate:

[0059] 1.1) In this embodiment, 6061 aluminum alloy is used as the substrate, and it is polished with 400#, 600#, 1000#, 1200#, 1500#, 2000#, 3000# and 4000# SiC water abrasive paper, and finally polished to a mirror surface with a diamond spray polishing agent with a particle size of 1.5μm and 0.5μm, respectively, to obtain a polished 6061 aluminum alloy.

[0060] 1.2) The polished 6061 aluminum alloy was ultrasonically cleaned in acetone, alcohol and deionized water for 20 minutes, and then dried to obtain the pretreated 6061 aluminum alloy.

[0061] Step 2, glow sputtering cleaning process:

[0062] 2.1) The pretreated 6061 aluminum alloy was fixed on a sample plate and then mounted on a workpiece turntable in a vacuum chamber of a magnetron sputtering device, and a pure copper target and a pure tin target were placed on target positions in the vacuum chamber of the magnetron sputtering device, respectively.

[0063] 2.2) After the vacuum degree of the sputtering chamber of the magnetron sputtering equipment is evacuated to 0.005Pa, argon gas is introduced and its flow rate is adjusted to 20sccm, the pressure in the sputtering chamber is controlled to be 0.5Pa, the bias power supply is turned on and the power is adjusted to -200W, and glow cleaning is performed for 20min to obtain a clean 6061 aluminum alloy.

[0064] Step 3, depositing a pure copper layer:

[0065] Argon gas was introduced into the vacuum chamber and its flow rate was adjusted to 20 sccm. The working gas pressure was controlled to 0.5 Pa. The power was turned on to sputter the copper target. The sputtering power was adjusted to 150 W and the sputtering time was 50 min. A 1 μm thick pure copper layer was formed on the clean 6061 aluminum alloy surface.

[0066] Step 4, depositing the copper-tin co-sputtered layer:

[0067] Argon gas was introduced into the vacuum chamber and its flow rate was adjusted to 20 sccm, the working gas pressure was controlled to 0.5 Pa, and the power supplies for controlling the copper target and the tin target were turned on at the same time. The sputtering power of the copper target was adjusted to 150 W, and the sputtering power of the tin target was adjusted to 80 W, so that the copper target and the tin target were deposited on the surface of the pure copper layer at the same time. The sputtering time was 125 min, so as to deposit a copper-tin co-sputtering layer with a thickness of 3 μm on the surface of the pure copper layer, and the atomic ratio of Cu and Sn in the copper-tin co-sputtering layer formed in this embodiment was 6.5:1.

[0068] Step 5, depositing a pure tin layer:

[0069] Argon gas was introduced into the vacuum chamber and its flow rate was adjusted to 20 sccm, the working gas pressure was controlled to 0.5 Pa, the power was turned on to sputter the tin target, the sputtering power was adjusted to 80 W, and the sputtering time was 50 min to deposit a pure tin layer with a thickness of 800 nm on the surface of the copper-tin co-sputtered layer.

[0070] After the coating is completed, ventilation is stopped and the vacuum state is maintained. The sample is taken out after cooling to room temperature in the furnace, and a Cu-Sn solder with a multilayer structure composed of a pure copper layer, a copper-tin co-sputtered layer and a pure tin layer is obtained on the surface of the substrate.

[0071] Example 3

[0072] This embodiment provides a Cu-Sn solder for a high reliability solder joint, and the Cu-Sn solder is prepared by the following steps:

[0073] Step 1, pretreatment of substrate:

[0074] 1.1) In this embodiment, 6061 aluminum alloy is used as the substrate, and it is polished with 400#, 600#, 1000#, 1200#, 1500#, 2000#, 3000# and 4000# SiC water abrasive paper, and finally polished to a mirror surface with a diamond spray polishing agent with a particle size of 1.5μm and 0.5μm, respectively, to obtain a polished 6061 aluminum alloy.

[0075] 1.2) The polished 6061 aluminum alloy was ultrasonically cleaned in acetone, alcohol and deionized water for 20 minutes, and then dried to obtain the pretreated 6061 aluminum alloy.

[0076] Step 2, glow sputtering cleaning process:

[0077] 2.1) The pretreated 6061 aluminum alloy was fixed on a sample plate and then mounted on a workpiece turntable in a vacuum chamber of a magnetron sputtering device, and a pure copper target and a pure tin target were placed on target positions in the vacuum chamber of the magnetron sputtering device, respectively.

[0078] 2.2) After the vacuum degree of the sputtering chamber of the magnetron sputtering equipment is evacuated to 0.005Pa, argon gas is introduced and its flow rate is adjusted to 20sccm, the pressure in the sputtering chamber is controlled to be 0.5Pa, the bias power supply is turned on and the power is adjusted to -200W, and glow cleaning is performed for 20min to obtain a clean 6061 aluminum alloy.

[0079] Step 3, depositing a pure copper layer:

[0080] Argon gas was introduced into the vacuum chamber and its flow rate was adjusted to 20 sccm. The working gas pressure was controlled to 0.5 Pa. The power was turned on to sputter the copper target. The sputtering power was adjusted to 150 W and the sputtering time was 50 min. A 1 μm thick pure copper layer was formed on the clean 6061 aluminum alloy surface.

[0081] Step 4, depositing the copper-tin co-sputtered layer:

[0082] Argon gas was introduced into the vacuum chamber and its flow rate was adjusted to 20 sccm, the working gas pressure was controlled to 0.5 Pa, and the power supplies for controlling the copper target and the tin target were turned on at the same time. The sputtering power of the copper target was adjusted to 150 W, and the sputtering power of the tin target was adjusted to 65 W, so that the copper target and the tin target were deposited on the surface of the pure copper layer at the same time. The sputtering time was 147 min, so as to deposit a copper-tin co-sputtering layer with a thickness of 3 μm on the surface of the pure copper layer, and the atomic ratio of Cu and Sn in the copper-tin co-sputtering layer formed in this embodiment was 9:1.

[0083] Step 5, depositing a pure tin layer:

[0084] Argon gas was introduced into the vacuum chamber and its flow rate was adjusted to 20 sccm, the working gas pressure was controlled to 0.5 Pa, the power was turned on to sputter the tin target, the sputtering power was adjusted to 80 W, and the sputtering time was 50 min to deposit a pure tin layer with a thickness of 800 nm on the surface of the copper-tin co-sputtered layer.

[0085] After the coating is completed, ventilation is stopped and the vacuum state is maintained. The sample is taken out after cooling to room temperature in the furnace, and a Cu-Sn solder with a multilayer structure composed of a pure copper layer, a copper-tin co-sputtered layer and a pure tin layer is obtained on the surface of the substrate.

[0086] Comparative Example 1

[0087] This comparative example provides a Cu-Sn solder, which is prepared by the following steps:

[0088] Step 1, pretreatment of substrate:

[0089] 1.1) In this comparative example, 6061 aluminum alloy was used as the substrate, and was polished with 400#, 600#, 1000#, 1200#, 1500#, 2000#, 3000# and 4000# SiC water abrasive paper, respectively, and finally polished to a mirror surface with a diamond spray polishing agent with a particle size of 1.5μm and 0.5μm, respectively, to obtain a polished 6061 aluminum alloy.

[0090] 1.2) The polished 6061 aluminum alloy was ultrasonically cleaned in acetone, alcohol and deionized water for 20 minutes, and then dried to obtain the pretreated 6061 aluminum alloy.

[0091] Step 2, glow sputtering cleaning process:

[0092] 2.1) The pretreated 6061 aluminum alloy was fixed on a sample plate and then mounted on a workpiece turntable in a vacuum chamber of a magnetron sputtering device, and a pure copper target and a pure tin target were placed on target positions in the vacuum chamber of the magnetron sputtering device, respectively.

[0093] 2.2) After the vacuum degree of the sputtering chamber of the magnetron sputtering equipment is evacuated to 0.005Pa, argon gas is introduced and its flow rate is adjusted to 20sccm, the pressure in the sputtering chamber is controlled to be 0.5Pa, the bias power supply is turned on and the power is adjusted to -200W, and glow cleaning is performed for 20min to obtain a clean 6061 aluminum alloy.

[0094] Step 3, depositing a pure copper layer:

[0095] Argon gas was introduced into the vacuum chamber and its flow rate was adjusted to 20 sccm. The working gas pressure was controlled to 0.5 Pa. The power was turned on to sputter the copper target. The sputtering power was adjusted to 150 W and the sputtering time was 150 min. A 3 μm thick pure copper layer was formed on the clean 6061 aluminum alloy surface.

[0096] Step 4, depositing a pure tin layer:

[0097] Argon gas was introduced into the vacuum chamber and its flow rate was adjusted to 20 sccm, the working gas pressure was controlled to 0.5 Pa, the power was turned on to sputter the tin target, the sputtering power was adjusted to 80 W, and the sputtering time was 63 min to deposit a pure tin layer with a thickness of 1 μm on the surface of the pure copper layer.

[0098] After the coating is completed, the ventilation is stopped and the vacuum state is maintained. After the furnace is cooled to room temperature, the sample is taken out to obtain a Cu-Sn solder composed of a pure copper layer and a pure tin layer formed on the surface of the substrate.

[0099] That is, the difference between this comparative example and Example 1 is only that:

[0100] In this comparative example, no copper-tin co-sputtering layer is formed.

[0101] Experimental Section

[0102] (I) Morphology test

[0103] The present invention takes the Cu-Sn solder prepared in Example 1 as an example, and performs a cross-sectional scanning electron microscope test on it. The test results are as follows: Figure 2 shown.

[0104] Figure 2 This is a cross-sectional scanning electron microscope image of the Cu-Sn solder prepared in Example 1. It can be seen that the Cu layer, the Cu / Sn co-sputtered layer and the Sn layer have relatively obvious boundaries, good crystallinity, and high film density and uniformity.

[0105] (II) Welding effect test

[0106] In the present invention, the Cu-Sn solders prepared in Examples 1 to 3 and Comparative Example 1 are respectively clamped in an offset alignment manner using a specific clamp, the bonding area is controlled to 15 mm × 10 mm, the bonding pressure is about 1 MPa, and transient liquid phase welding is performed to obtain welded samples.

[0107] The transient liquid phase welding conditions are: keeping warm at 300°C for 180 minutes.

[0108] The Cu-Sn solders of Examples 1 to 3 all have good soldering effects. The Cu-Sn solder of Comparative Example 1 has poor soldering effects.

[0109] The present invention also tests the shear strength of the welded samples corresponding to Examples 1 to 3 and Comparative Example 1, respectively, and the test method is to use a universal testing machine with model UTM6409 to perform the shear strength test.

[0110] The test results show that the strength of Example 1 is 35.4MPa, the strength of Example 2 is 46.8MPa, the strength of Example 3 is 17.9MPa, and the strength of Comparative Example 1 is 10.6MPa. In Example 2, the ratio of copper to tin is just enough to bond to form a full Cu3Sn phase, and the combination is good without holes, so the bonding strength of the Cu-Sn solder in Example 2 is the highest, which is 46.8MPa. The intermetallic compound finally generated in Example 1 is the Cu3Sn phase, but due to a slight excess of Sn, after bonding, it was found that there were holes in the bonding interface after scanning electron microscopy testing and observation, so the strength is lower than that of Example 2, which is 35.4MPa. In Example 3, since the intermetallic compound finally generated is the Cu6Sn5 phase, the bonding strength is low, which is 17.9MPa. In Comparative Example 1, due to the long-distance diffusion of copper and tin, a large number of holes are formed, so the bonding strength is the lowest, which is only 10.6MPa.

[0111] Obviously, the above embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

Claims

1. A method for preparing a Cu-Sn solder for a high reliability welding joint, characterized in that: The following steps are involved: polishing and then cleaning the substrate to obtain a pretreated substrate; Performing glow sputtering cleaning on the pretreated substrate to obtain a clean substrate; In an argon atmosphere, magnetron sputtering technology is used to deposit a pure copper layer on the surface of the clean substrate using a copper target as a sputtering target; Using a copper target and a tin target as co-sputtering target materials, depositing them on the surface of the pure copper layer at the same time, so as to deposit a copper-tin co-sputtering layer on the surface of the pure copper layer; Using a tin target as a sputtering target, a pure tin layer is deposited on the surface of the copper-tin co-sputtering layer to form a Cu-Sn solder having a multi-layer structure composed of a pure copper layer, a copper-tin co-sputtering layer and a pure tin layer on the surface of the substrate; In the copper-tin co-sputtered layer, the atomic ratio of Cu to Sn is 5 to 9:

1.

2. The method for preparing the Cu-Sn solder according to claim 1, characterized in that: In the Cu-Sn solder, the atomic ratio of Cu to Sn is 3.36:1 to 2.

36.

3. The method for preparing the Cu-Sn solder according to claim 1, characterized in that: When depositing the copper-tin co-sputtering layer, argon gas is introduced to control the working gas pressure to be 0.1Pa-1Pa; During sputtering deposition, the sputtering power of the copper target is controlled to be 100W-150W, the sputtering power of the tin target is controlled to be 65W-100W, and the deposition time is controlled to be 110min-147min.

4. The method for preparing the Cu-Sn solder according to claim 1, characterized in that: When depositing the pure copper layer, argon gas is introduced to control the working gas pressure to be 0.1Pa-1Pa; and during sputtering deposition, the sputtering power of the copper target is controlled to be 140W-160W, and the deposition time is 40min-60min.

5. The method for preparing the Cu-Sn solder according to claim 1, characterized in that: When depositing the pure tin layer, argon gas is introduced to control the working gas pressure to be 0.1Pa-1Pa; and during sputtering deposition, the sputtering power of the tin target is controlled to be 70W-90W, and the deposition time is 40min-60min.

6. The method for preparing the Cu-Sn solder according to claim 1, characterized in that: The glow sputtering cleaning process is performed by the following steps: Evacuate to a background vacuum degree of ≤0.005Pa, introduce argon gas, adjust the argon gas flow rate to 15sccm~25sccm, and control the working gas pressure to 0.4Pa~1.6Pa; apply a bias voltage of -500V~-200V to the substrate, and the glow cleaning time is 10min~20min.

7. The method for preparing the Cu-Sn solder according to claim 1, characterized in that: The polishing is carried out by the following steps: polishing with 400#, 600#, 1000#, 1200#, 1500#, 2000#, 3000# and 4000# SiC water-abrasive sandpaper respectively, and finally polishing with a diamond spray polishing agent to a mirror surface.

8. A Cu-Sn solder for a high-reliability solder joint prepared by the preparation method according to any one of claims 1 to 7, characterized in that: The Cu-Sn solder has a multilayer structure of a pure copper layer, a copper-tin co-sputtered layer and a pure tin layer in sequence from the inside to the outside on the surface of the substrate.

9. The Cu-Sn solder for a high reliability solder joint according to claim 8, characterized in that: The thickness of the pure copper layer is 0.8 μm to 1.2 μm.

10. The Cu-Sn solder for a high reliability solder joint according to claim 8, characterized in that: The thickness of the pure tin layer is 0.6 μm to 1 μm.

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