Solder paste formula capable of reducing welding spot holes and preparation process

Abstract

The invention relates to the technical field of solder paste production, in particular to a solder paste formula capable of reducing solder joint holes and a preparation process. The solder paste formula capable of reducing solder joint holes comprises tin, silver, copper, rosin, a solvent, a trace additive element group package, a curing group package, a reduction group package, antimony, manganese, glutaric acid, benzotriazole and a surfactant. According to the process, stable electrical connection is provided by reducing welding spot cavities, and a larger and more continuous path is formed in a welding spot due to small cavity current, so that the phenomenon of current crowding is reduced, and local overheating and potential signal interruption risks are avoided; the welding spots are not only electrically connected, but also key heat conduction paths of power devices such as a CPU, a GPU and a power MOSFET, metal is a good heat conductor, the cavities are heat insulators, the welding spots with small cavities are lower in thermal resistance, heat generated by a chip can be more efficiently transmitted to a PCB and dissipated, the junction temperature of the chip can be directly reduced, and the small cavities are used for preventing the devices from being overheated, so that the reliability of the device is improved. And the long-term reliability is ensured.

Description

Technical Field

[0001] This invention relates to the field of solder paste production technology, specifically a solder paste formula and preparation process that can reduce voids in solder joints. Background Technology

[0002] Solder joint voids refer to tiny air bubbles or cavities that form inside a solder joint. They typically occur during reflow soldering and are commonly found on the bottom of devices such as BGA and QFN or in the solder joints of through-hole components. The main cause is that gases generated during the soldering process fail to escape in time before the solder solidifies and are trapped inside.

[0003] Small size and a small number of voids are generally permissible and accepted by IPC standards. However, large size and a high proportion of voids reduce the effective conductive / thermal conductive area, which may lead to: ① decreased electrical reliability, increased current density, and localized overheating. ② weakened mechanical strength, becoming the starting point for crack initiation. ③ deteriorated thermal conductivity, affecting the heat dissipation of power components.

[0004] Traditional solder paste, due to its highly volatile solvents, highly active and residual flux system, and potential powder oxidation, collectively leads to the following problems during reflow: 1. Large total gas generation; 2. Rapid and concentrated gas generation; 3. Poor gas escape channels. These three factors combined make it easy for unvented gases to be trapped during the solder's transition from paste to liquid and then to solid, ultimately forming solder joint voids. Therefore, for high-reliability products such as automotive electronics, aerospace, or devices with stringent void ratio requirements, such as BGA and QFN, upgrading from traditional solder paste to a dedicated low-voidity solder paste is one of the most direct and effective material solutions for reducing solder joint void ratio. Combined with improvements to existing processes and design optimizations, void problems can be systematically controlled to an optimal level. To this end, the inventors propose a solder paste formulation and preparation process that reduces solder joint voids to address the aforementioned technical problems related to reducing solder joint void ratio. Summary of the Invention

[0005] To overcome the shortcomings mentioned above, the invention aims to provide a technical solution that can solve the above problems.

[0006] A solder paste formulation that reduces voids in solder joints, characterized in that the formulation is prepared according to the following mass fractions: Tin 60-80 parts, silver 2-3.5 parts, copper 0.5-2.5 parts, rosin 1-10 parts, solvent 1-10 parts, trace element grouping package 1 part, curing grouping package 1 part, reduction grouping package 1 part, antimony powder 0.5-1 part, manganese powder 0.3-0.7 parts, glutaric acid 0.5-1 part, benzotriazole 1-1.2 parts, surfactant 0.8-1 part.

[0007] Furthermore, the solvent is one of diethylene glycol monobutyl ether, terpineol, and ethyl lactate, and the surfactant is a high-acid-value solder paste surfactant.

[0008] Furthermore, the trace element grouping package includes 2-3 parts nickel powder, 0.6-1.3 parts germanium powder, and 0.5-2 parts bismuth powder.

[0009] Furthermore, the reducing group package includes 0.5-1 parts of indium powder and 1-2.5 parts of cobalt powder.

[0010] Furthermore, the solidified aggregate package includes 0.1-0.2 parts of aluminum powder and 0.1-0.2 parts of iron powder.

[0011] A solder paste preparation process that reduces solder joint voids, the process comprising the following steps: S1: Atomization and classification: 60-80 parts of tin, 2-3.5 parts of silver, and 0.5-2.5 parts of copper are atomized through an atomization system to obtain solder alloy powder. After classification and sieving, solder alloy powder with different particle sizes is obtained. S2: Preliminary mixing: Mix solder alloy powder with 1-0 parts rosin, 1-10 parts diethylene glycol monobutyl ether, 0.5-1 parts antimony powder, and 0.3-0.7 parts manganese powder, and place the mixture in a pre-prepared mixing device for stirring. Rosin and solvent provide suitable viscosity and thixotropy to ensure the forming state of the solder paste. During the stirring process, add surfactant dropwise to prevent collapse. After removal, let stand for 1-2 hours to obtain paste A. S3: Preheating and mixing. After preheating the mixing equipment, place paste A in the mixing equipment for secondary mixing. At the same time, add 0.5-1 parts of glutaric acid, 1-1.2 parts of benzotriazole, and 0.8-1 parts of high acid value solder paste activator in sequence. After stirring for 2-3 minutes, add 2-3 parts of nickel powder, 0.6-1.3 parts of germanium powder, 0.5-2 parts of bismuth powder, 0.5-1 parts of indium powder, and 1-2.5 parts of cobalt powder in sequence. The mixture is initially dissolved and evenly mixed with paste A to obtain a mixed paste. S4: Vacuum degassing. A vacuum mixer is used to vacuum stir the mixed paste to remove air entrained during the mixing process, directly reducing the air bubbles contained in the mixed paste and suppressing solder joint voids from the source. The stirring speed is 300-350 rpm, the stirring environment is a vacuum state, the pressure is ≤ -0.09 MPa, and the stirring time is 10-15 minutes. At the same time, 0.1-0.2 parts of aluminum powder and 0.1-0.2 parts of iron powder are added in sequence in this step. After thorough stirring, a semi-finished flux paste is obtained. S5: Cooling at room temperature. The obtained semi-finished flux is allowed to stand and cool. The storage temperature is 23±3°C, the humidity is <60%, and the standing time is 4-6 hours. After standing at room temperature, the semi-finished flux is placed in a cold storage room for cooling. The cold storage temperature is 2-10°C to obtain the finished flux. S6: Low-temperature vacuum stirring. The finished solder paste is stirred in a vacuum mixer at a speed of 100-200 rpm. The stirring environment is a vacuum state with a pressure of ≤ -0.09 MPa and a stirring time of 5-8 minutes to obtain the finished solder paste. S7: Packaging and storage. The finished solder paste is packaged into bottles of different colors according to whether it is environmentally friendly. Random sampling is conducted, and after labeling, it is stored in the warehouse. The solder paste should be stored in a refrigerator at 2-10 degrees Celsius.

[0012] Furthermore, in S1, the atomization system is ultrasonic atomization, the atomizing gas pressure is 3–10 MPa, and the cooling rate is 10. 3 -10 6 K / s, this cooling rate can suppress segregation and obtain a uniform structure. The powder after atomization has high sphericity, which is conducive to printing rolling and dense stacking. The oxygen content is <100ppm to avoid poor wetting and increased voids caused by excessive oxygen content. The classification method adopts airflow classification, which uses a turbine airflow classifier to separate particles of different sizes based on their settling velocity differences in the airflow. The particle size is cut to 30-40μm, while retaining fine powder <35μm and removing coarse powder >41μm.

[0013] Furthermore, in S2, the mixing equipment is a planetary mixer or a double planetary power mixer, with a mixing speed of 500–800 rpm and a mixing time of 5–10 minutes.

[0014] Furthermore, in step S3, the preheating temperature is 120–180°C, the preheating time is 60–90 s, the heating rate is 1–2°C / s, the stirring speed is 200–400 rpm, and the stirring time is 10–15 min. This process activates glutaric acid and allows the solvent to evaporate slowly, avoiding violent boiling that could generate gas and increase the probability of bubbles and pores. It also works with benzotriazole to form a protective film on the copper surface to prevent high-temperature re-oxidation. A low-speed mode is used to avoid high-speed shearing that could cause oxidation or breakage of the metal powder. This process ensures that the alloy powder and paste A are fully mixed to prevent clumping.

[0015] Furthermore, in step S6, the low-temperature stirring temperature is 5-8°C. By stirring, the metal powder that may have settled is redispersed evenly, and the interfacial bonding between the flux and the metal powder is restored. This avoids poor wetting caused by insufficient flux in some areas due to delamination, which could lead to voids during soldering.

[0016] Compared with the prior art, the beneficial effects of the present invention are: 1. Superior Electrical Reliability ① Stable Electrical Connection: Voids are insulating and non-conductive, allowing smaller void currents to have a larger and more continuous path within the solder joint. This reduces current congestion and avoids the risk of localized overheating and potential signal interruption; ② Low Resistance and Loss: A larger conductive cross-sectional area results in lower overall solder joint resistance. This reduces energy loss (IL) in high-current applications such as power modules and power devices. 2 R loss) and heat generation; ③ Better high-frequency performance: In high-frequency circuits, the geometry and integrity of solder joints affect signal integrity. Smaller and fewer voids provide a more uniform dielectric environment, reduce signal reflection and distortion, and help maintain impedance stability; 2. Mechanical integrity ① Increased mechanical strength: Large voids will significantly weaken the structure of the solder joint and become stress concentration points. When subjected to vibration, impact, or mechanical bending, cracks can easily propagate from the edge of large cavities, leading to solder joint failure. Solder joints with smaller cavities are much stronger and more durable. ② Increased fatigue resistance: Electronic products undergo thermal expansion and contraction during operation due to power cycling and changes in ambient temperature. This thermal stress can cause solder joint fatigue. Solder joints with smaller cavities have a denser internal structure, which can distribute stress more evenly, thereby extending their thermal fatigue life. 3. Thermal management performance ① Efficient heat conduction path: Solder joints are not only electrical connections but also key heat conduction paths for power devices such as CPUs, GPUs, and power MOSFETs. Metals are good thermal conductors, while cavities are thermal insulators. Solder joints with smaller cavities have lower thermal resistance, which can more efficiently transfer the heat generated by the chip to the PCB and dissipate it. This can directly reduce the junction temperature of the chip. Small cavities help prevent device overheating and ensure long-term reliability. 4. Improve quality ① Reduce early failure: Potential defects caused by large voids such as poor soldering and high resistance are one of the important reasons for early product failure. Controlling the size of voids can effectively reduce the defect rate and early rework rate. Keeping voids within a stable and small range ensures the quality of every product leaving the factory. Detailed Implementation

[0017] The present invention will now be described in further detail with reference to specific embodiments.

[0018] In this first embodiment, please refer to a specific implementation of a solder paste formula that can reduce solder joint voids. The formula is characterized by being prepared according to the following mass fractions: The composition includes 60 parts tin, 2 parts silver, 0.5 parts copper, 3 parts rosin, 4 parts solvent, 1 part trace element additive grouping package, 1 part curing grouping package, 1 part reduction grouping package, 0.5 parts antimony powder, 0.3 parts manganese powder, 0.6 parts glutaric acid, 1 part benzotriazole, and 0.8 parts surfactant. The solvent is diethylene glycol monobutyl ether, and the surfactant is a high-acid-value tin paste activator. The trace element additive grouping package includes 1 part nickel powder, 0.7 parts germanium powder, and 0.8 parts bismuth powder. The reduction grouping package includes 0.5 parts indium powder and 1 part cobalt powder. The curing grouping package includes 0.1 parts aluminum powder and 0.1 parts iron powder.

[0019] A solder paste preparation process that reduces solder joint voids, the process comprising the following steps: S1: Atomization and Grading. 60 parts tin, 2 parts silver, and 0.5 parts copper are atomized through an atomization system to obtain solder alloy powder. After grading and sieving, solder alloy powder with different particle sizes is obtained. The atomization system is ultrasonic atomization with an atomization pressure of 5 MPa and a cooling rate of 10³ K / s. This cooling rate can suppress segregation and obtain a uniform structure. The powder after atomization has high sphericity, which is beneficial for printing, rolling, and dense stacking. The oxygen content is <100 ppm to avoid poor wetting and increased voids caused by excessive oxygen content. The classification method adopts airflow classification, which uses a turbine airflow classifier to separate particles of different sizes based on their settling velocity differences in the airflow, cutting the particle size to 31μm, while retaining fine powder <35μm and removing coarse powder >41μm. S2: Preliminary mixing: Mix solder alloy powder with 4 parts rosin, 1 part diethylene glycol monobutyl ether, 0.5 parts antimony powder, and 0.3 parts manganese powder, then place the mixture in a pre-prepared mixing device for stirring. Rosin and solvent provide suitable viscosity and thixotropy to ensure the forming state of the solder paste. During the stirring process, add surfactant dropwise to prevent collapse. After removal, let stand for 1.2 hours to obtain paste A. The mixing device uses a planetary mixer or a double planetary power mixer, with a stirring speed of 550 rpm and a time of 6 minutes. The quality and ratio of solder alloy powder mixed with rosin directly affect the performance of solder paste. Rosin acts as a binder, binding the solder alloy powder, antimony powder, and manganese powder together to form a uniform mixture. Antimony is added in this solder paste preparation process to increase strength without affecting wettability, while manganese can inhibit oxidation and improve wetting. Diethylene glycol monobutyl ether has excellent solubility, effectively dissolving rosin to aid in the mixing of metal powders, thereby improving the fluidity and coating effect of the coating. Secondly, diethylene glycol monobutyl ether has a low evaporation rate, which can maintain a stable solvent state for a longer period of time, reducing the phenomenon of solder paste solidification and clumping.

[0020] S3: Preheating and Mixing. After preheating the mixing equipment, place paste A in the mixing equipment for secondary stirring. Simultaneously, add 0.6 parts glutaric acid, 1 part benzotriazole, and 0.8 parts high-acid-value solder paste activator sequentially. After stirring for 2 minutes, add 2 parts nickel powder, 0.7 parts germanium powder, 0.8 parts bismuth powder, 0.5 parts indium powder, and 1 part cobalt powder sequentially. These components are initially dissolved and uniformly mixed with paste A to obtain a mixed paste. The preheating temperature is 135°C, the preheating time is 80 seconds, the heating rate is 1.5°C / s, the stirring speed is 200 rpm, and the stirring time is 10 minutes. This process activates glutaric acid and allows the solvent to evaporate slowly, avoiding violent boiling that could generate gas and increase the probability of bubbles and porosity. It also works with benzotriazole to form a protective film on the copper surface, preventing high-temperature re-oxidation. A low-speed mode is used to avoid high-speed shearing that could cause oxidation or breakage of the metal powder. This process ensures that the alloy powder and paste A are fully mixed to prevent clumping. Bismuth can significantly lower the melting point and improve wettability, forming a tin-bismuth eutectic. It locally liquefies before the main alloy melts, promoting capillary climbing and reducing voids caused by the pillow effect. Glutaric acid is the main activator, which removes oxidation and is easily volatile. After volatilization, it can reduce the rate of reaction, thereby stabilizing the reaction effect of the solder paste and avoiding continuous activation. Benzotriazole and high-acid-value solder paste activators respectively act as copper corrosion inhibitors, reducing the surface tension of the molten solder from ~500mN / m to ~300mN / m, making it easier for bubbles to coalesce, rise, and escape. This, combined with the [Cu(I)BTA] formed on the copper pads by benzotriazole... n The polymer film prevents copper re-oxidation under high reflow temperature, avoids wetting voids, prevents re-oxidation and reduces the overall surface tension of the solder paste, and promotes the venting effect. Combined with the activating deoxygenation, high activity and high volatility of glutaric acid, it fully reacts and completely vents during the preheating stage, leaving no residual gas source. Germanium forms a reducing atmosphere on the surface of the molten solder, preventing tin oxidation, greatly increasing the wetting angle, and enabling the solder to spread quickly and vent the gas. Welding materials composed of indium and tin have the characteristics of low melting point, good wettability and excellent welding performance. Indium has a low melting point and good wettability, which can improve the tensile strength and corrosion resistance of the welded joint. Nickel and copper compete to form (Cu,Ni)6Sn5, which inhibits the porosity formed by high temperature aging and reduces some porosity, thus playing a complementary role. S4: Vacuum degassing. A vacuum mixer is used to vacuum stir the mixed paste to remove air entrained during the mixing process, directly reducing the air bubbles contained in the mixed paste and suppressing solder joint voids from the source. The stirring speed is 300-350 rpm, the stirring environment is a vacuum state, the pressure is ≤ -0.09 MPa, and the stirring time is 10-15 minutes. At the same time, 0.1 parts of aluminum powder and 0.1 parts of iron powder are added in sequence in this step. After thorough stirring, a semi-finished flux paste is obtained. Cobalt has a high thermal fatigue resistance and is easy to repair. The metal is magnetic. The effect of cobalt on iron powder increases the adhesion of solder paste and avoids the formation of air bubbles inside the solder during soldering, which can cause voids. Aluminum has a low melting point. Combined with the viscosity of aluminum after melting, it can increase the tightness of the connection between iron powder and cobalt after coating them. S5: Cooling at room temperature. The obtained semi-finished flux is allowed to stand and cool. The storage temperature is 23±3°C, the humidity is <60%, and the standing time is 4 hours. After standing at room temperature, the semi-finished flux is placed in a cold storage room for cooling at 3°C ​​to obtain the finished flux. S6: Low-temperature vacuum stirring. The finished solder paste is stirred in a vacuum mixer at a speed of 100 rpm. The stirring environment is a vacuum state with a pressure ≤ -0.09 MPa and a stirring time of 5 minutes to obtain the finished solder paste. The low-temperature stirring temperature is 5°C. By stirring, the metal powder that may have settled is redispersed evenly, and the interface bonding between the flux and the metal powder is restored. This avoids poor wetting caused by insufficient flux in some areas due to delamination, which can lead to voids during soldering. S7: Packaging and storage. The finished solder paste is packaged into bottles of different colors according to whether it is environmentally friendly. Random sampling is conducted, and after labeling, it is stored in the warehouse. The solder paste must be stored in a refrigerator at 3 degrees Celsius.

[0021] Example 1 is a high-metal-content type, suitable for scenarios requiring high reliability and low voids. This example has a metal content of approximately 90% and uses less flux. It uses diethylene glycol monobutyl ether, which has a high boiling point and low evaporation rate, making it suitable for slow reflow. The addition of 0.7% Ge and 0.8% Bi provides strong antioxidant properties and improves wetting. The cobalt / indium combination enhances thermal fatigue performance, minimizing solder joint voids to <8%. It leaves minimal residue after reflow, requires no cleaning, and has good compatibility. The use of metal filler improves thermal conductivity, facilitating heat dissipation. It is suitable for nitrogen reflow and stepped temperature curve processes. Detailed implementation data can be found in Table 1 for comparison.

[0022] In this second embodiment, please refer to a specific implementation of a solder paste formulation that can reduce solder joint voids. The formulation is characterized by the following mass fractions: 70 parts tin, 2.5 parts silver, 1 part copper, 6 parts rosin, 7 parts solvent, 1 part trace element additive grouping packet, 1 part curing grouping packet, 1 part reduction grouping packet, 0.7 parts antimony powder, 0.5 parts manganese powder, 0.6 parts glutaric acid, 1 part benzotriazole, and 1 part surfactant. The solvent is terpineol, and the surfactant is a high-acid-value solder paste activator. The trace element additive grouping packet includes 2.5 parts nickel powder, 1 part germanium powder, and 1 part bismuth powder. The reduction grouping packet includes 0.7 parts indium powder and 2 parts cobalt powder. The curing grouping packet includes 0.2 parts aluminum powder and 0.2 parts iron powder.

[0023] A solder paste preparation process that can reduce solder joint voids is provided. This preparation process is used to prepare a solder paste formulation that can reduce solder joint voids. The preparation process is the same as in Example 1.

[0024] Example 2: This example focuses on the balanced ratio of metal to flux. It uses general high-density surface mount technology and terpineol to achieve low cost and moderate volatility. The combination of 2.5 parts nickel and 2.0 parts cobalt can improve cold stability, so as to increase the range of long-term light throughput and short-term high throughput. Increasing the manganese / antimony content can enhance high-temperature creep resistance, resulting in improved printability, good thixotropy, and reduced collapse. It is suitable for high-density packaging such as 0201, 0.4mm CSP, and BGA, offering the best overall cost and performance. It is suitable for mass production of consumer electronics and communication equipment and can be used with gas or nitrogen reflow processes. For detailed implementation data, please refer to Table 1 for comparison.

[0025] In this third embodiment, please refer to a specific implementation of a solder paste formula that can reduce solder joint voids, characterized in that the formula is prepared according to the following mass fractions: The composition includes 80 parts tin, 3.5 parts silver, 0.5 parts copper, 9 parts rosin, 9 parts solvent, 1 part trace element additive grouping package, 1 part curing grouping package, 1 part reduction grouping package, 0.8 parts antimony powder, 0.6 parts manganese powder, 1 part glutaric acid, 1.2 parts benzotriazole, and 1 part surfactant; the solvent is ethyl lactate, and the surfactant is a high-acid-value solder paste activator; the trace element additive grouping package includes 2.8 parts nickel powder, 1 part germanium powder, and 1 part bismuth powder; the reduction grouping package includes 0.8 parts indium powder and 2 parts cobalt powder; and the curing grouping package includes 0.2 parts aluminum powder and 0.2 parts iron powder. A solder paste preparation process that can reduce solder joint voids is provided. This preparation process is used to prepare a solder paste formulation that can reduce solder joint voids. The preparation process is the same as in Example 1.

[0026] Example 3: This high-activity / high-wetting method is suitable for difficult-to-solder surfaces or low-temperature soldering scenarios. The flux ratio is 18 parts with the highest content. Glutaric acid 1.0 part combined with benzotriazole 1.2 parts has the strongest activity. Ethyl lactate is used because it is a bio-based material with environmentally friendly and fast-evaporating characteristics. Silver 3.5 parts can improve strength. Bismuth 1.0 part + indium 0.8 parts lower the effective melting point, enabling reflow at 210–220°C. The high content of surfactant 1 part reduces surface tension, thereby reducing the wetting angle to <25°, making it suitable for difficult-to-solder surfaces such as OSP, ENIG, and Immersion Silver. It is also suitable for low-temperature soldering, avoiding damage to heat-sensitive components. This embodiment has strong exhaust capacity, and the ultra-fine pitch of Type 5 / 6 results in good control of welding voids. Ethyl lactate is an environmentally friendly solvent that complies with RoHS / REACH. It is suitable for 5G RF modules, flexible circuits, medical electronics, and other applications with high environmental requirements. It can be used as an export product. For detailed implementation data, please refer to Table 1 for comparison.

[0027] Table 1 is a comparison table of the various embodiments: Table 2 summarizes the synergistic effects of key components based on Examples 1, 2, and 3. Table 3 is a comparison table of application scenarios based on Examples 1, 2, and 3. The above description, in conjunction with specific preferred embodiments, provides a further detailed explanation of the present invention. It should not be construed that the specific implementation of the present invention is limited to these descriptions. For those skilled in the art, various simple deductions or substitutions can be made without departing from the inventive concept, and all such modifications and substitutions should be considered within the scope of protection of the present invention.

Claims

1. A solder paste formula that reduces voids in solder joints, characterized in that, This formula is prepared according to the following mass fractions: Tin 60-80 parts, silver 2-3.5 parts, copper 0.5-2.5 parts, rosin 1-10 parts, solvent 1-10 parts, trace element grouping package 1 part, curing grouping package 1 part, reduction grouping package 1 part, antimony powder 0.5-1 part, manganese powder 0.3-0.7 parts, glutaric acid 0.5-1 part, benzotriazole 1-1.2 parts, surfactant 0.8-1 part.

2. The solder paste formulation for reducing solder joint voids according to claim 1, characterized in that, The solvent is one of diethylene glycol monobutyl ether, terpineol, and ethyl lactate, and the surfactant is a high-acid-value solder paste surfactant.

3. The solder paste formulation for reducing solder joint voids according to claim 1, characterized in that, The trace element grouping package includes 2-3 parts nickel powder, 0.6-1.3 parts germanium powder, and 0.5-2 parts bismuth powder.

4. The solder paste formulation for reducing solder joint voids according to claim 1, characterized in that, The reducing group package includes 0.5-1 parts indium powder and 1-2.5 parts cobalt powder.

5. The solder paste formulation for reducing solder joint voids according to claim 1, characterized in that, The solidified aggregate package includes 0.1-0.2 parts aluminum powder and 0.1-0.2 parts iron powder.

6. A solder paste preparation process that can reduce solder joint voids, characterized in that: This preparation process is used in the solder paste formulation for reducing solder joint voids as described in any one of claims 1-5, and the preparation process includes the following steps: S1: Atomization and classification: 60-80 parts of tin, 2-3.5 parts of silver, and 0.5-2.5 parts of copper are atomized through an atomization system to obtain solder alloy powder. After classification and sieving, solder alloy powder with different particle sizes is obtained. S2: Preliminary mixing: Mix solder alloy powder with 1-0 parts rosin, 1-10 parts diethylene glycol monobutyl ether, 0.5-1 parts antimony powder, and 0.3-0.7 parts manganese powder, and place the mixture in a pre-prepared mixing device for stirring. Rosin and solvent provide suitable viscosity and thixotropy to ensure the forming state of the solder paste. During the stirring process, add surfactant dropwise to prevent collapse. After removal, let stand for 1-2 hours to obtain paste A. S3: Preheating and mixing. After preheating the mixing equipment, place paste A in the mixing equipment for secondary mixing. At the same time, add 0.5-1 parts of glutaric acid, 1-1.2 parts of benzotriazole, and 0.8-1 parts of high acid value solder paste activator in sequence. After stirring for 2-3 minutes, add 2-3 parts of nickel powder, 0.6-1.3 parts of germanium powder, 0.5-2 parts of bismuth powder, 0.5-1 parts of indium powder, and 1-2.5 parts of cobalt powder in sequence. The mixture is initially dissolved and evenly mixed with paste A to obtain a mixed paste. S4: Vacuum degassing. A vacuum mixer is used to vacuum stir the mixed paste to remove air entrained during the mixing process, directly reducing the air bubbles contained in the mixed paste and suppressing solder joint voids from the source. The stirring speed is 300-350 rpm, the stirring environment is a vacuum state, the pressure is ≤ -0.09 MPa, and the stirring time is 10-15 minutes. At the same time, 0.1-0.2 parts of aluminum powder and 0.1-0.2 parts of iron powder are added in sequence in this step. After thorough stirring, a semi-finished flux paste is obtained. S5: Cooling at room temperature. The obtained semi-finished flux is allowed to stand and cool. The storage temperature is 23±3°C, the humidity is <60%, and the standing time is 4-6 hours. After standing at room temperature, the semi-finished flux is placed in a cold storage room for cooling. The cold storage temperature is 2-10°C to obtain the finished flux. S6: Low-temperature vacuum stirring. The finished solder paste is stirred in a vacuum mixer at a speed of 100-200 rpm. The stirring environment is a vacuum state with a pressure of ≤ -0.09 MPa and a stirring time of 5-8 minutes to obtain the finished solder paste. S7: Packaging and storage. The finished solder paste is packaged into bottles of different colors according to whether it is environmentally friendly. Random sampling is conducted, and after labeling, it is stored in the warehouse. The solder paste should be stored in a refrigerator at 2-10 degrees Celsius.

7. The solder paste preparation process for reducing solder joint voids according to claim 6, characterized in that, In S1, the atomization system is ultrasonic atomization, the atomizing gas pressure is 3–10 MPa, and the cooling rate is 10. 3 -10 6 K / s, this cooling rate can suppress segregation and obtain a uniform structure. The powder after atomization has high sphericity, which is conducive to printing rolling and dense stacking. The oxygen content is <100ppm to avoid poor wetting and increased voids caused by excessive oxygen content. The classification method adopts airflow classification, which uses a turbine airflow classifier to separate particles of different sizes based on their settling velocity differences in the airflow. The particle size is cut to 30-40μm, while retaining fine powder <35μm and removing coarse powder >41μm.

8. The solder paste preparation process for reducing solder joint voids according to claim 6, characterized in that, In S2, the mixing equipment is a planetary mixer or a double planetary power mixer, with a mixing speed of 500–800 rpm and a mixing time of 5–10 minutes.

9. A solder paste preparation process for reducing solder joint voids according to claim 6, characterized in that, In step S3, the preheating temperature is 120–180°C, the preheating time is 60–90s, the heating rate is 1–2°C / s, the stirring speed is 200–400 rpm, and the stirring time is 10–15min.

10. The solder paste preparation process for reducing solder joint voids according to claim 6, characterized in that: In step S6, the low-temperature stirring temperature is 5-8°C. Stirring helps to evenly disperse any metal powder that may have settled, restoring the interfacial bonding between the flux and the metal powder.

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