Low-temperature high-strength neutral solder paste and method for manufacturing the same

Abstract

The application discloses a low-temperature high-strength neutral soldering paste and a manufacturing method thereof. The soldering paste has the following raw material formula in percentage by weight: 87-92% of tin-based alloy powder, 3.5-5% of activating agent, 0.5-1.2% of reinforcing agent, 0.5-2% of thixotropic agent and 2-6% of solvent. The alloy components in the tin-based alloy powder and their percentage by weight are as follows: 90-95% of Sn, 2-5% of Ag, 0.2-1% of Cu and 2-6% of Bi. The activating agent is composed of dimethylol propionic acid, sodium phosphate and ammonium fluoroborate according to a weight ratio of 1: (0.1-0.4): (1.5-2). The reinforcing agent comprises reinforcing alumina particles subjected to metallization treatment, and the reinforcing alumina particles have a nanoscale particle size. The soldering paste has the characteristics of low welding temperature, good wettability, improved solder joint shear strength, neutral no post-welding corrosion and the like, and is suitable for precise welding scenes.

Description

Technical Field

[0001] This invention relates to the field of solder paste technology, and in particular to a low-temperature, high-strength neutral solder paste and its preparation method. Background Technology

[0002] With the development of new energy and high-power devices, the application of stainless steel welding is increasing. However, there are several problems in stainless steel welding: ① Traditional tin-silver-copper solders have poor wettability on the surface of stainless steel workpieces (wetting angle > 55°), requiring the use of strong acid fluxes (such as hydrochloric acid fluxes), which leads to severe post-weld corrosion; ② The alloy layer of the brazed joint is discontinuous, which causes the Cr2O3 oxide layer on the surface of the stainless steel workpiece to hinder the formation of the Fe-Sn alloy layer, thus affecting the welding quality; ③ Currently available stainless steel solder pastes or fluxes have strong post-weld corrosiveness, requiring post-weld cleaning to ensure that the solder joints do not continue to corrode, further increasing the complexity of the process and production costs.

[0003] In view of this, the present invention is hereby proposed. Summary of the Invention

[0004] To overcome the above-mentioned defects, the present invention provides a low-temperature high-strength neutral solder paste and its preparation method. The preparation method is simple, reasonable and easy to operate, and the resulting solder paste has the characteristics of low welding temperature, good wettability, ability to improve the shear strength of the solder joint, and neutrality without post-soldering corrosion. It can be well applied to precision welding scenarios such as robot charging terminals and smart home devices.

[0005] The technical solution adopted by the present invention to solve its technical problem is: a low-temperature high-strength neutral solder paste, which, by weight percentage, has the following raw material formula: 87%–92% tin-based alloy powder, 3.5%–5% activator, 0.5%–1.2% reinforcing agent, 0.5%–2% thixotropic agent, and 2%–6% solvent; Based on the total weight of the tin-based alloy powder, the alloy composition and its weight percentage in the tin-based alloy powder are: Sn 90%–95%, Ag 2%–5%, Cu 0.2%–1%, and Bi 2%–6%. The activator is composed of dimethylolpropionic acid, sodium phosphate and ammonium fluoroborate in a weight ratio of 1:(0.1-0.4):(1.5-2); the reinforcing agent includes metallized reinforced alumina particles with a particle size in the nanometer range.

[0006] As a further improvement of the present invention, based on the total weight of the tin-based alloy powder and by weight percentage, the tin-based alloy powder is composed of 92.5% Sn, 3% Ag, 0.5% Cu and 4% Bi.

[0007] As a further improvement of the present invention, the tin-based alloy powder has a particle size of 15-25 μm and an oxygen content of no more than 200 ppm.

[0008] As a further improvement of the present invention, the enhanced alumina particles are composed of alumina particles and a nickel layer plated on the surface of the alumina particles, and the particle size of the enhanced alumina particles is 10-30 nm.

[0009] As a further improvement of the present invention, the reinforcing agent further includes a silane coupling agent, wherein the weight ratio of the reinforced alumina particles to the silane coupling agent is 1:(0.2-0.5).

[0010] As a further improvement of the present invention, the thixotropic agent is a modified fatty acid amide, the solvent is methyl glycolate, and the weight ratio of the thixotropic agent to the solvent is 1:(2-5).

[0011] This invention also provides a method for preparing low-temperature, high-strength neutral solder paste, comprising the following steps: S1: Tin-based alloy powder with a particle size of 15-25μm and an oxygen content of no more than 200ppm is obtained by atomization powder preparation process; S2: After mixing the thixotropic agent and solvent in the prescribed amount, add the dimethylolpropionic acid, sodium phosphate and ammonium fluoroborate in the prescribed amount, and mix thoroughly again to obtain the first mixture; S3: After soaking the reinforcing agent in the formula amount, add it to the obtained first mixture and stir thoroughly until the reinforcing agent is evenly dispersed to obtain the second mixture; S4: Add the tin-based alloy powder and the resulting second mixture to a planetary mixer at a vacuum degree of 10. 2 Pa~10 -1 The low-temperature, high-strength neutral solder paste is obtained by stirring at a speed of 50-60 rpm for 30-50 minutes.

[0012] As a further improvement of the present invention, it also includes S5: the obtained low-temperature high-strength neutral solder paste is subjected to homogenization and centrifugal degassing treatment in sequence to obtain the finished product of the low-temperature high-strength neutral solder paste.

[0013] As a further improvement of the present invention, in S5 above, the obtained low-temperature high-strength neutral solder paste is subjected to three three-roll mill treatments so that the viscosity of the low-temperature high-strength neutral solder paste is controlled at 180±20 Pa·s.

[0014] As a further improvement of the present invention, in S5 above, the low-temperature high-strength neutral solder paste after homogenization is transferred to a centrifugal degassing machine and degassed for 3 to 5 minutes at a speed of 1000 to 1500 rpm to obtain the finished product of the low-temperature high-strength neutral solder paste.

[0015] The beneficial effects of this invention are: ① Through technological innovation, this invention produces a solder paste with characteristics such as low welding temperature, good wettability, improved solder joint shear strength, and neutrality without post-solder corrosion. It is well-suited for precision welding applications such as robot charging terminals and smart home devices, and can reduce costs by more than 60%. ② The solder paste manufacturing method provided by this invention is simple, reasonable, and easy to operate, and the related raw materials are readily available, inexpensive, and more environmentally friendly. Detailed Implementation

[0016] The present invention will be further described in detail below with reference to specific embodiments, but the present invention is not limited to these embodiments.

[0017] This application discloses a low-temperature, high-strength neutral solder paste and its preparation method. The method is simple, reasonable, and easy to operate. The resulting solder paste exhibits characteristics such as low soldering temperature, good wettability, improved solder joint shear strength, and neutrality without post-soldering corrosion. It is well-suited for precision soldering applications such as robot charging terminals and smart home devices. The key to this achievement lies in the optimized and innovative formulation of the solder paste's raw materials. Specific details are as follows: 1. To prepare the low-temperature, high-strength neutral solder paste described in this application;

[0018] Example 1:

[0019] This embodiment 1 provides a method for preparing low-temperature high-strength neutral solder paste, which mainly includes the following steps: S1: Tin-based alloy powder with a particle size of 15-25 μm and an oxygen content of no more than 200 ppm is obtained by atomization powder preparation process.

[0020] Specifically, the specific method for preparing the tin-based alloy powder used in this embodiment is as follows: S11: By weight percentage, a Sn-Ag-Cu-Bi alloy composed of 92.5% Sn, 3% Ag, 0.5% Cu, and 4% Bi is produced under a vacuum of 10... 5 Pa~10 2 The alloy melt was obtained by melting under the conditions of Pa and a melting temperature of 850℃. S12: The obtained alloy melt is processed into tin-based alloy powder with a particle size of 15-25 μm (preferably 20 μm ± 2 μm) and an oxygen content of no more than 200 ppm by an atomization powdering process. Understandably, based on the composition of the Sn-Ag-Cu-Bi alloy described above, the chemical formula of the tin-based alloy powder can be written as Sn92.5Ag3Cu0.5Bi4.

[0021] S2: Mix 1 kg of modified fatty acid amide and 4 kg of methyl glycolate at 75℃~80℃, then add 1.4 kg of dimethylolpropionic acid, 0.28 kg of sodium phosphate and 2.52 kg of ammonium fluoroborate, and mix thoroughly again to obtain the first mixture. S3: Mix and impregnate 0.625 kg of reinforced alumina particles and 0.225 kg of silane coupling agent (KH-550), then add the mixture to the first mixture obtained and stir thoroughly until the reinforcing agent is evenly dispersed to obtain the second mixture. Note: The reinforced alumina particles are composed of alumina particles and a nickel layer plated on the surface of the alumina particles. Therefore, the chemical formula of the reinforced alumina particles can be written as Ni@Al2O3. In addition, the particle size of the reinforced alumina particles is preferably controlled to be 10-30 nm (more preferably 20 nm).

[0022] S4: Add 89.95 kg of tin-based alloy powder (Sn92.5Ag3Cu0.5Bi4) and the resulting second mixture into a planetary mixer, and heat to a vacuum of 10... 2 Pa~10 -1 The low-temperature, high-strength neutral solder paste is obtained by stirring at a speed of 50-60 rpm for 30-50 minutes.

[0023] Furthermore, in this embodiment, a stirring speed of 50 rpm and a stirring time of 40 min are preferred.

[0024] S5: The obtained low-temperature high-strength neutral solder paste is subjected to homogenization and centrifugal degassing treatment in sequence to obtain the finished product of the low-temperature high-strength neutral solder paste.

[0025] The homogenization process involves passing the obtained low-temperature high-strength neutral solder paste through a three-roll mill three times, with the gap between the rollers in the three-roll mill controlled to be ≤10μm, so that the viscosity of the low-temperature high-strength neutral solder paste is controlled at 180±20Pa·s.

[0026] The centrifugal degassing process is as follows: After homogenization, the low-temperature high-strength neutral solder paste is filled and packaged, then transferred to a centrifugal degassing machine and degassed for 3 to 5 minutes at a speed of 1000 to 1500 rpm to obtain the finished low-temperature high-strength neutral solder paste.

[0027] Furthermore, in this embodiment, a rotation speed of 1500 rpm and a degassing time of 3 min are preferred.

[0028] Example 2:

[0029] This embodiment 2 also provides a method for preparing low-temperature high-strength neutral solder paste. Compared with embodiment 1, the difference of embodiment 2 is that the solder paste raw material formula used in embodiment 2 is different from that in embodiment 1.

[0030] Specifically, the solder paste raw material formula used in this embodiment 2 is as follows: 1.75Kg of modified fatty acid amide, 5.25Kg of methyl glycolate, 1.5Kg of dimethylolpropionic acid, 0.6Kg of sodium phosphate, 2.4Kg of ammonium fluoroborate, 0.7Kg of reinforced alumina particles, 0.35Kg of silane coupling agent (KH-550) and 87.45Kg of tin-based alloy powder (Sn92.5Ag3Cu0.5Bi4).

[0031] Note: Apart from the differences mentioned above, the specific processing methods and parameters used in each step of this Example 2, such as melting parameters, stirring and mixing parameters, homogenization parameters, centrifugation and degassing parameters, are the same as in Example 1; therefore, they will not be repeated here.

[0032] Example 3:

[0033] This embodiment 3 also provides a method for preparing low-temperature high-strength neutral solder paste. Compared with embodiment 1, the difference of embodiment 3 is that the raw material formula of the solder paste used in embodiment 3 is different from that in embodiment 1.

[0034] Specifically, the solder paste raw material formula used in this embodiment 3 is as follows: 1 kg of modified fatty acid amide, 3 kg of methyl glycolate, 1.2 kg of dimethylolpropionic acid, 0.24 kg of sodium phosphate, 2.16 kg of ammonium fluoroborate, 0.4 kg of reinforced alumina particles, 0.2 kg of silane coupling agent (KH-550) and 91.8 kg of tin-based alloy powder (Sn91.3Ag4Cu0.7Bi4).

[0035] Notes: ① Apart from the differences mentioned above, the specific processing methods and parameters used in each step of this Example 3, such as melting parameters, stirring and mixing parameters, homogenization parameters, and centrifugal degassing parameters, are the same as in Example 1; therefore, they will not be repeated here. ② It is understood that, by weight percentage, the tin-based alloy powder used in this Example 3 is composed of a compound of 91.3% Sn, 4% Ag, 0.7% Cu, and 4% Bi.

[0036] 2. Performance testing of the solder paste prepared in this application; The solder pastes prepared in Examples 1-3 of this application and a traditional chlorine-containing stainless steel solder paste (comparative example) were subjected to performance tests. The test methods were as follows: Step 1) Clean the 304 stainless steel sheet with a length, width, and thickness of 20mm × 20mm × 1mm and the T2 copper plate with a length, width, and thickness of 8mm × 8mm with isopropanol.

[0037] Step 2) The solder paste prepared in Examples 1 to 3 of this application and the traditional chlorine-containing stainless steel solder paste are printed on 304 stainless steel sheets respectively, and the printing thickness of the above four solder pastes is 0.15mm. Then, the T2 copper plate is attached to the printed solder paste.

[0038] Step 3) Place the prepared workpiece (i.e., the combination of 304 stainless steel sheet and T2 copper plate) into a reflow oven under nitrogen atmosphere protection (oxygen content less than 100ppm) for welding. The reflow chain speed is set to 1.2m / min, the heating rate is set to 2℃ / s, the peak temperature of the welding zone is set to 250℃, and the welding time is set to about 35s.

[0039] Step 4) After welding is completed, the weldment is subjected to wetting angle test, resistivity test, shear strength test, thermal conductivity test, salt spray test, copper mirror test, and ion contamination test, respectively. Among them, the wetting angle test is carried out in accordance with the test standard JIS Z 3197; the resistivity test is carried out in accordance with the test standard ASTM B193 (four-probe method); the shear strength test is carried out in accordance with the test standard GB / T 11363; the salt spray test is carried out in accordance with the test standard GB / T2423.17-2024; the thermal conductivity test is carried out in accordance with the LFA 467 laser flash method; the copper mirror test is carried out in accordance with IPC TM-650 2.3.32; and the ion contamination test is carried out in accordance with IPC TM-650 2.3.28.

[0040] Table 1 below shows the performance test results of the solder paste prepared in Examples 1-3 of this application and the conventional chlorine-containing stainless steel solder paste.

[0041] Table 1 Performance test results of solder pastes obtained in Examples 1-3 of this application and traditional chlorine-containing stainless steel solder paste As shown in Table 1: ① When soldering with the solder paste prepared in this application, a wetting angle of 16°–18° can be achieved, which is much smaller than the 52° wetting angle when soldering with traditional chlorine-containing stainless steel solder paste. This indicates that the solder paste prepared in this application has excellent wettability on stainless steel workpieces and a tight bond. ② When soldering with the solder paste prepared in this application, the shear strength at the solder joint can reach 25–28 MPa, which is twice the shear strength at the solder joint after soldering with traditional chlorine-containing stainless steel solder paste (14 MPa). This indicates that a high-strength solder alloy layer (IMC layer) can be formed when soldering with the solder paste prepared in this application. ③ When soldering with the solder paste prepared in this application, the resistivity at the solder joint does not exceed 13 μΩ·cm and the thermal conductivity is greater than 69 W / mk, which is better than the resistivity and thermal conductivity at the solder joint after soldering with traditional chlorine-containing stainless steel solder paste. This indicates that a good metallurgical bond is formed between the solder paste prepared in this application and the stainless steel workpiece, resulting in excellent soldering quality. ④ When using the solder paste prepared in this application for soldering, the stainless steel parts can be soldered without corrosion or penetration, which is far superior to the post-soldering condition of traditional chlorine-containing stainless steel solder paste. ⑤ When using the solder paste prepared in this application for soldering, the ion contamination level is very low (maximum only 1.03 μg / cm³). 2 The ion contamination level is far lower than that of traditional chlorine-containing stainless steel solder paste (5.6 μg / cm³). 2 This indicates that the cleanliness of the solder joints and the soldering environment is extremely high when using the solder paste obtained in this application.

[0042] The reason why the solder paste obtained in this application can achieve the above advantages is mainly due to the optimization and innovation of the raw material formula of the solder paste. Specifically, it is reflected in the following: ① When preparing the solder paste, this application selects a tin-based alloy powder composed of four metal elements, Sn, Ag, Cu and Bi, in a specific formula. Among them, Bi can lower the melting point of the solder paste (the melting point of the solder paste obtained in this application is 217℃ according to DSC measurement, which can reliably weld stainless steel and copper materials together at 250℃) and suppress Cu6Sn5 brittleness, so that the solder joint alloy layer (IMC layer) has a certain toughness; Ag can improve the wettability of the solder paste, thereby ensuring the continuity of the solder joint alloy layer (IMC layer). ② In formulating the solder paste, this application uses an activator composed of dimethylolpropionic acid, sodium phosphate, and ammonium fluoroborate in a specific weight ratio. Ammonium fluoroborate selectively corrodes the oxide layer on the surface of stainless steel, effectively removing the oxide layer and thus improving the wettability of the solder paste. Sodium phosphate forms a temporary protective film to reduce post-soldering corrosion. Furthermore, the combination of sodium phosphate and ammonium fluoroborate neutralizes the acidic byproducts produced by ammonium fluoroborate corrosion, preventing excessive localized corrosion. Dimethylolpropionic acid assists ammonium fluoroborate in accelerating the dissolution of oxides on the surface of stainless steel, further improving the wettability of the solder paste. ③ In formulating the solder paste, this application uses metallized reinforced alumina particles as a reinforcing agent, which significantly improves the density of the solder joint alloy layer (IMC layer), thereby significantly improving the shear strength at the solder joint. In addition, the tin plating layer on the reinforced alumina particles also has functions such as stress transfer, improved thermal conductivity, reduced soldering temperature, maintenance of solder paste fluidity, and enhanced bonding between alumina particles and other components. ④ In the preparation of solder paste, this application optimizes the control of each component to make the solder paste neutral (pH value 6.5-7.1), ensuring that the post-soldering residue is close to neutral, can pass the 48-hour salt spray corrosion test and copper mirror test, and the post-soldering residue can be removed without cleaning, which is both environmentally friendly and cost-effective.

[0043] In addition to optimizing and innovating the raw material formula of solder paste as described above, this application also adopts a preferred combination of processes, especially atomization powdering, vacuum stirring, homogenization, and centrifugal degassing, which can effectively ensure the uniform texture and excellent performance of solder paste.

[0044] In summary, this application, through technological innovation, has produced a solder paste with characteristics such as low welding temperature, good wettability, improved solder joint shear strength, and neutrality without post-solder corrosion. It is well-suited for precision welding scenarios such as robot charging terminals and smart home devices, and can reduce costs by more than 60%.

[0045] Many specific details have been set forth in the foregoing description to provide a thorough understanding of the present invention. However, the above description is merely a preferred embodiment of the present invention, and the present invention can be implemented in many other ways different from those described herein. Therefore, the present invention is not limited to the specific embodiments disclosed above. Furthermore, any person skilled in the art can make many possible variations and modifications to the technical solutions of the present invention, or modify them into equivalent embodiments, using the methods and techniques disclosed above, without departing from the scope of the present invention. Any simple modifications, equivalent changes, and modifications made to the above embodiments based on the technical essence of the present invention, without departing from the content of the present invention, shall still fall within the protection scope of the present invention.

Claims

1. A low-temperature, high-strength neutral solder paste, characterized in that: The raw material formula, by weight percentage, is as follows: 87%–92% tin-based alloy powder, 3.5%–5% activator, 0.5%–1.2% reinforcing agent, 0.5%–2% thixotropic agent, and 2%–6% solvent; Based on the total weight of the tin-based alloy powder, the alloy composition and its weight percentage in the tin-based alloy powder are: Sn 90%–95%, Ag 2%–5%, Cu 0.2%–1%, and Bi 2%–6%. The activator is composed of dimethylolpropionic acid, sodium phosphate, and ammonium fluoroborate in a weight ratio of 1:(0.1-0.4):(1.5-2); the reinforcing agent includes metallized reinforced alumina particles and a silane coupling agent. The reinforced alumina particles consist of alumina particles and a nickel layer plated on the surface of the alumina particles, and the particle size of the reinforced alumina particles is 10-30 nm. The weight ratio of the reinforced alumina particles to the silane coupling agent is 1:(0.2-0.5). The thixotropic agent is a modified fatty acid amide, the solvent is methyl glycolate, and the weight ratio of the thixotropic agent to the solvent is 1:(2-5).

2. The low-temperature high-strength neutral solder paste according to claim 1, characterized in that: Based on the total weight of the tin-based alloy powder and by weight percentage, the tin-based alloy powder is composed of 92.5% Sn, 3% Ag, 0.5% Cu and 4% Bi.

3. The low-temperature high-strength neutral solder paste according to claim 1, characterized in that: The tin-based alloy powder has a particle size of 15–25 μm and an oxygen content of no more than 200 ppm.

4. A method for preparing a low-temperature, high-strength neutral solder paste as described in any one of claims 1-3, characterized in that: The production process includes the following steps: S1: Tin-based alloy powder with a particle size of 15-25μm and an oxygen content of no more than 200ppm is obtained by atomization powder preparation process; S2: After mixing the thixotropic agent and solvent in the prescribed amount, add the dimethylolpropionic acid, sodium phosphate and ammonium fluoroborate in the prescribed amount, and mix thoroughly again to obtain the first mixture; S3: After soaking the reinforcing agent in the formula amount, add it to the obtained first mixture and stir thoroughly until the reinforcing agent is evenly dispersed to obtain the second mixture; S4: Add the tin-based alloy powder and the resulting second mixture to a planetary mixer at a vacuum degree of 10. 2 Pa~10 -1 The low-temperature, high-strength neutral solder paste is obtained by stirring at a speed of 50-60 rpm for 30-50 minutes.

5. The method for preparing low-temperature high-strength neutral solder paste according to claim 4, characterized in that: It also includes S5: the obtained low-temperature high-strength neutral solder paste is subjected to homogenization and centrifugal degassing treatment in sequence to obtain the finished product of the low-temperature high-strength neutral solder paste.

6. The method for preparing low-temperature high-strength neutral solder paste according to claim 5, characterized in that: In step S5 above, the obtained low-temperature high-strength neutral solder paste is subjected to three three-roll mill treatments to control the viscosity of the low-temperature high-strength neutral solder paste at 180±20 Pa·s.

7. The method for preparing low-temperature high-strength neutral solder paste according to claim 5, characterized in that: In step S5 above, the homogenized low-temperature high-strength neutral solder paste is transferred to a centrifugal degassing machine and degassed for 3 to 5 minutes at a speed of 1000 to 1500 rpm to obtain the finished low-temperature high-strength neutral solder paste.

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