A high-thermal-conductivity Sn-In-Ag-Zn alloy solder, a preparation method and application thereof

Abstract

A high-thermal-conductivity Sn-In-Ag-Zn alloy solder as well as a preparation method and application thereof belong to the technical field of lead-free solders. The purpose of the present application is to solve the technical problem that the pure In solder for the existing thermal interface material cannot simultaneously consider high thermal conductivity, dimensional stability and interface service reliability. The high-thermal-conductivity Sn-In-Ag-Zn alloy solder according to the present application is composed of In: 70-90%, Ag: 0.01-5%, Zn: 0-20% and the balance of Sn in terms of atomic percentage. The present application selects Sn, In, Ag and Zn as the composition elements of the solder, and a new lead-free solder alloy without lead element with high thermal conductivity, low interface thermal resistance and high reliability is obtained by adjusting the proportion, which can be used to replace the pure In solder as the thermal interface material and applied to the field of electronic packaging.

Description

Technical Field

[0001] This invention belongs to the field of lead-free solder technology, specifically relating to a high thermal conductivity Sn-In-Ag-Zn alloy solder, its preparation method, and its application. Background Technology

[0002] As electronic devices such as integrated circuits, power devices, artificial intelligence chips, and power modules for new energy vehicles continue to develop towards higher power density, higher integration, and miniaturization, the heat generated by chips during operation increases significantly, and the internal heat flux density of devices continues to rise. If the heat generated by the chip cannot be conducted to the heat dissipation structure in a timely manner and effectively released, it will lead to an increase in the chip junction temperature, which in turn will cause device performance degradation, thermal failure, and even damage to the packaging structure. Therefore, reducing the interfacial thermal resistance between the chip and the heat sink and improving the overall heat dissipation capacity of the packaging structure have become important problems that urgently need to be solved in the field of electronic packaging.

[0003] Thermal interface materials are typically placed between chips, substrates, heat sinks, or heat sinks to fill the microscopic voids at the contact interface and improve interfacial heat transfer performance. While traditional polymer-based thermal interface materials offer some compressibility and process adaptability, their intrinsic thermal conductivity is low, limiting their heat dissipation capacity in high heat flux density electronic devices. Metal-based thermal interface materials, on the other hand, possess high thermal conductivity, effectively reducing interfacial thermal resistance and holding significant application value in high-power electronic packaging heat dissipation.

[0004] Among existing metal-based thermal interface materials, pure indium (In) possesses a low melting point, good plastic deformation capability, and high thermal conductivity, allowing it to form a good bond with the contact surface under certain pressure or temperature conditions. Therefore, it is often used as a high-performance thermal interface material or a low-temperature solder. However, pure indium still has certain shortcomings in actual service. For example, pure indium has low mechanical strength and is prone to creep, extrusion, or decreased shape stability under long-term thermal cycling, pressure loading, or high-temperature service conditions. Simultaneously, pure indium exhibits poor wetting between itself and the substrate or metallization layer, potentially leading to interfacial reactions that affect interfacial bonding stability and long-term service reliability. Furthermore, pure indium materials have limitations in melting characteristics, microstructure stability, wetting behavior, and mechanical property control, making it difficult to simultaneously meet the comprehensive requirements of high thermal conductivity, low interfacial thermal resistance, and high reliability. Therefore, there is an urgent need to develop a high thermal conductivity In-based solder alloy suitable for electronic packaging heat dissipation, providing a new material solution to replace pure indium thermal interface materials and meeting the demands of high-power chip packaging for efficient heat dissipation and long-term reliability. Summary of the Invention

[0005] The purpose of this invention is to solve the technical problem that existing pure In solders for thermal interface materials cannot simultaneously achieve high thermal conductivity and reliable interface operation. Therefore, this invention provides a high thermal conductivity Sn-In-Ag-Zn alloy solder, its preparation method, and its applications.

[0006] The technical solution of the present invention is as follows: One of the objectives of this invention is to provide a high thermal conductivity Sn-In-Ag-Zn alloy brazing filler metal, wherein the filler metal has the following atomic percentages: In: 70~90%, Ag: 0.01~5%, Zn: 0~20%, and the balance is Sn.

[0007] Further specified, the percentage of Zn atoms in the brazing filler metal is 5-15%.

[0008] Further specifying, the percentage of Ag atoms in the solder is 2-5%.

[0009] The second objective of this invention is to provide a method for preparing a high thermal conductivity Sn-In-Ag-Zn alloy solder, the method comprising the following steps: S1: Weigh high-purity Sn, In, Ag, and Zn metal powders according to the component ratio, and place them in a quartz glass tube and seal it under vacuum. S2: Place the quartz glass tube in a swingable tube furnace for melting and cool to obtain an alloy ingot; S3: Completely coat the alloy ingot with rosin, heat it to 200-400℃ in an induction melting furnace, and hold it at that temperature for 20-40 minutes, stirring it every 10 minutes during the process. After holding at that temperature, pour it into a graphite mold to obtain the alloy brazing filler metal.

[0010] Further specified, the purity of Sn, In, Ag and Zn metal powders in S1 is ≥99.99%.

[0011] Further specifying, in S1, the metal powder is placed into the quartz glass tube in order of melting point from high to low.

[0012] Further specified, the melting temperature in S2 is 750-850℃, the time is 1.5-2.5h, and the heating rate is 8-12℃ / min.

[0013] Furthermore, the melting temperature in S2 is 800℃, the melting time is 2 hours, and the heating rate is 10℃ / min.

[0014] Further specified, the temperature in S3 is heated to 300°C and held for 30 minutes.

[0015] The third objective of this invention is to provide a high thermal conductivity Sn-In-Ag-Zn alloy solder as a thermal interface material for use in the field of electronic packaging.

[0016] The advantages of this invention compared to existing technologies are: This invention selects Sn, In, Ag, and Zn as solder constituent elements, and by adjusting their proportions, obtains a novel lead-free solder alloy that combines high thermal conductivity, low interfacial thermal resistance, and high reliability. Specific advantages are as follows: (1) The Sn-In-Ag-Zn solder of the present invention has a lower melting point than pure In solder and has a thermal conductivity comparable to that of pure In solder. It also exhibits better wettability than pure In and can be used to replace pure In solder to meet the requirements of thermal interface materials.

[0017] (2) The Sn-In-Ag-Zn brazing filler metal preparation method of the present invention is simple, requires simple smelting equipment, requires low preparation temperature and low energy consumption, has good anti-oxidation effect, and is easy to apply to industrial production. It can avoid defects such as component segregation and casting cracks caused by the rapid cooling of the alloy liquid during the casting process. Attached Figure Description

[0018] Figure 1 The image shows the differential scanning calorimetry (DSC) curve of the solder obtained in Example 1. Figure 2 The differential scanning calorimetry (DSC) curve of the solder obtained in Example 2 is shown below. Figure 3 The image shows the differential scanning calorimetry (DSC) curve of the solder obtained in Example 3. Figure 4 This is a cross-sectional SEM image of the solder joint on the Cu substrate surface obtained in Example 1. Figure 5 This is a SEM image of the cross-sectional area of ​​the solder joint on the Cu substrate surface obtained in Example 2. Figure 6 This is a cross-sectional SEM image of the solder joint on the Cu substrate surface obtained in Example 3. Figure 7 The image shows a cross-sectional SEM image of the solder joint on the Cu substrate surface obtained in Comparative Example 1. Figure 8 This is a SEM image of the cross-sectional area of ​​the solder joint on the Ag substrate surface obtained in Example 1. Figure 9 This is a SEM image of the cross-section of the solder joint on the Ag substrate surface obtained in Example 2. Figure 10 This is a SEM image of the cross-sectional area of ​​the solder joint on the Ag substrate surface obtained in Example 3. Figure 11 The image shows a cross-sectional SEM image of the solder joint on the Ag substrate surface obtained in Comparative Example 1. Figure 12 The diagram shows the mechanical properties of the solders obtained in Examples 1-3. Detailed Implementation

[0019] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0020] Unless otherwise specified, the experimental methods used in the following examples are conventional methods. Unless otherwise specified, the materials, reagents, methods, and instruments used are all conventional materials, reagents, methods, and instruments in the art, and can be obtained commercially by those skilled in the art.

[0021] Example 1: The preparation method of the high thermal conductivity Sn-In-Ag-Zn alloy solder in this example is carried out according to the following steps: S1: By atomic percentage, In: 73%, Ag: 2%, Zn: 15%, balance Sn (total amount 100at%). Weigh Sn, In, Ag, and Zn metal powders (purity ≥99.99%) and place them into a quartz glass tube in order of melting point from high to low. Vacuum seal the tube and introduce Ar into it during sealing to fully expel the air inside. S2: Place the quartz glass tube in a swingable tube furnace and heat it to 800°C at a heating rate of 10°C / min. Then, hold it at 800°C for 2 hours for melting. During the holding process, the tube furnace is swung. Remove the tube and cool it to obtain the alloy ingot. S3: Completely coat the alloy ingot with rosin, heat it to 300°C in an induction melting furnace, and hold it at that temperature for 30 minutes, stirring it every 10 minutes during the process. After holding at that temperature, pour it into a graphite mold to obtain Sn-In-Ag-Zn alloy brazing filler metal.

[0022] Example 2: The difference between this embodiment and Embodiment 1 is that the solder composition in S1 is: In: 84 at%, Ag: 4 at%, Zn: 5 at%, with the balance being Sn (total amount 100 at%). Other steps and parameters are the same as in Embodiment 1.

[0023] Example 3: The difference between this embodiment and Embodiment 1 is that the solder composition in S1 is: In: 87 at%, Ag: 2 at%, with the balance being Sn (total amount 100 at%). Other steps and parameters are the same as in Embodiment 1.

[0024] Comparative Example 1: Pure In solder.

[0025] Example 1: DSC test The melting behavior of the solder alloy was characterized using a DSC (Digital Substance Conversion) simultaneous thermal analyzer. During testing, a 15 mg solder sample was placed in a DSC test crucible. The phase transformation process and melting characteristics of the solder alloy were analyzed by recording the endothermic and exothermic signals of the sample during the heating process. The results are as follows: Figure 1-3 As shown in Table 1, the melting point of the solder of this invention is comparable to that of pure In solder.

[0026] Example 2: Wettability Test The wetting properties of solder alloy on Cu / Ag substrates were tested using the seated drop method. A 99.99% pure copper / silver sheet with dimensions of 5 mm × 5 mm × 2 mm was used as the substrate. Before the test, the substrate surface was ground and polished to remove surface oxide layers, oil stains, and other impurities, minimizing the influence of the substrate surface condition on the wetting results. 30 mg of solder alloy was weighed and placed on the treated substrate surface, and KINGBO RMA-218 flux was added to aid wetting. The sample was placed on a heating stage for reflow heating to fully melt the solder and spread it on the substrate surface. After cooling, the sample was ultrasonically cleaned with alcohol to remove residual flux and contaminants. The sample was then resin-mounted. After the resin cured, the mounted sample was progressively ground and polished until the central region of the solder joint cross-section was exposed. After polishing, the sample surface was sputter-coated with gold, and the cross-sectional morphology of the solder joint was observed using a scanning electron microscope. The contact angle between the solder alloy and the substrate was measured using the ContactAngle plugin in ImageJ software, and the contact angle size was used to characterize the wetting performance of the solder on the substrate. The results are as follows: Figure 4-11 As shown in Table 1, the solders of Examples 1-3 exhibit small wetting angles on both Cu and Ag substrates. In particular, Examples 1 and 2 show wetting angles of only 12.6° and 7.2° on Cu substrates, respectively, and 17.6° and 10.8° on Ag substrates, respectively. This demonstrates that the solders of the present invention possess excellent wetting and spreading capabilities. In contrast, Comparative Example 1 shows a wetting angle of 28.4° on a Cu substrate, indicating poor wetting performance.

[0027] Example 3: Uniaxial tensile test: First, the brazing filler metal ingots obtained from casting were prepared into specimens: the ingots were cut into standard tensile specimens using wire cutting. After cutting, the specimen surfaces were polished with 1000# sandpaper to remove cutting marks and surface oxide layers, ensuring a smooth and defect-free surface to avoid surface imperfections affecting the test results. The tensile specimen dimensions were: plate thickness a = 2 mm, plate width b = 5 mm, parallel section end radius r = 5 mm, original gauge length L = 12 mm, test temperature 23±5 ℃ (room temperature), tensile rate 3 mm / min, and corresponding strain rate 4.17×10⁻⁶. -3 s-1 The tensile properties of the brazing alloy samples obtained after the experiment are shown in the figure below. Figure 12 As shown in Table 1, the tensile strength and total elongation at break of the brazing alloys were obtained from the curve. To reduce experimental error and ensure the reliability of the test results, at least three parallel samples were tested for each brazing alloy, and the final experimental result was the average of the test data of all parallel samples. The results show that the brazing alloys of Examples 1-3 maintain excellent wettability while exhibiting good strength and toughness.

[0028] Example 4: Thermal conductivity test The alloy was processed into sheet-shaped samples with a size of 10. 10 The sample thickness is 2mm, ensuring the upper and lower surfaces are flat and parallel, free from obvious oxidation, scratches, and pores. The sample density, specific heat capacity, and thermal diffusivity are tested. The thermal diffusivity test is performed by placing the sample in the sample holder of a laser flare instrument under a nitrogen atmosphere. A laser pulse irradiates the lower surface of the sample, and the instrument records the temperature rise curve of the upper surface. The thermal diffusivity is calculated based on the temperature rise response.

[0029] Thermal conductivity is calculated using the following formula:

[0030] in Thermal conductivity, α Where is the thermal diffusivity, ρ For density, C p Specific heat capacity.

[0031] The results are recorded in Table 1.

[0032] Table 1

[0033] The thermal conductivity of Examples 1 and 2 reached 80.8 W / (m·K) and 90.8 W / (m·K) respectively, demonstrating good thermal conductivity and meeting the requirements for efficient heat dissipation.

[0034] The above description is merely a preferred embodiment of the present invention. These specific embodiments are different implementations based on the overall concept of the present invention, and the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A high thermal conductivity Sn-In-Ag-Zn alloy solder, characterized in that, The brazing filler metal, by atomic percentage, is: In: 70~90%, Ag: 0.01~5%, Zn: 0~20%, with the balance being Sn.

2. The alloy brazing filler metal according to claim 1, characterized in that, The percentage of Zn atoms in the brazing filler metal is 5-15%.

3. The alloy brazing filler metal according to claim 1, characterized in that, The percentage of Ag atoms in the brazing filler metal is 2-5%.

4. The method for preparing the high thermal conductivity Sn-In-Ag-Zn alloy solder according to any one of claims 1-3, characterized in that, The method described: S1: Weigh high-purity Sn, In, Ag, and Zn metal powders according to the component ratio, and place them in a quartz glass tube and seal it under vacuum. S2: Place the quartz glass tube in a swingable tube furnace for melting and cool to obtain an alloy ingot; S3: Completely coat the alloy ingot with rosin, heat it to 200-400℃ in an induction melting furnace, and hold it at that temperature for 20-40 minutes, stirring it every 10 minutes during the process. After holding at that temperature, pour it into a graphite mold to obtain the alloy brazing filler metal.

5. The method according to claim 4, characterized in that, The purity of Sn, In, Ag, and Zn metal powders in S1 is ≥99.99%.

6. The method according to claim 4, characterized in that, In S1, metal powders are placed into the quartz glass tube in order of their melting points from high to low.

7. The method according to claim 4, characterized in that, The smelting temperature in S2 is 750-850℃, the time is 1.5-2.5h, and the heating rate is 8-12℃ / min.

8. The method according to claim 7, characterized in that, The melting temperature in S2 is 800℃, the melting time is 2 hours, and the heating rate is 10℃ / min.

9. The method according to claim 4, characterized in that, Heat to 300°C in S3 and hold for 30 minutes.

10. The application of the high thermal conductivity Sn-In-Ag-Zn alloy solder according to any one of claims 1-3 as a thermal interface material in the field of electronic packaging.

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