Ultralow porosity laser solder paste and method of making same

Abstract

The present application relates to the technical field of tin paste, in particular to a kind of ultra-low void rate laser soldering tin paste and preparation method thereof.Ultra-low void rate laser soldering tin paste includes the following raw materials by mass percentage:Sn-Ag-Cu-In alloy 80%~90%, microcapsule flux 8%~10%, rare earth additive 0.15%~0.4%, nano mesoporous silica 0.3%~0.8% and modified polyamide wax 0.9%~2.1%.The ultra-low void rate laser soldering tin paste can realize very low void rate (≤3%) after laser welding, while having uniform and moderate thickness IMC layer, excellent appearance performance and excellent thermal fatigue resistance, effectively solving the problem of high void rate of traditional soldering tin paste and poor solder joint reliability.

Description

Technical Field

[0001] This invention relates to the field of solder paste technology, specifically to an ultra-low void ratio laser solder paste and its preparation method. Background Technology

[0002] Solder paste, as a core interconnect material in surface mount technology (SMT) and electronic packaging, directly determines the reliability and lifespan of electronic products through its soldering quality. With the development of electronic products towards higher density, miniaturization, and higher reliability, laser soldering has gradually become the preferred process for precision soldering due to its advantages such as localized heating, small heat-affected zone, and flexible processes. However, traditional solder pastes generally suffer from high void ratios during laser soldering. Voids significantly reduce the conductivity, thermal conductivity, and mechanical strength of solder joints, and in severe cases, can even lead to cracking and failure. Furthermore, existing solder pastes still have shortcomings in terms of wettability, oxidation resistance, and long-term reliability, making it difficult to meet the demands of high-reliability applications such as aerospace, automotive electronics, and 5G communications. Therefore, developing a laser solder paste with ultra-low void ratio, excellent wettability, and high reliability has significant practical importance and market value. Summary of the Invention

[0003] In order to overcome the shortcomings and deficiencies of the existing technology, the purpose of this invention is to provide an ultra-low void ratio laser solder paste. This ultra-low void ratio laser solder paste can achieve an extremely low void ratio (≤3%) after laser soldering, while having a uniform and moderately thick IMC layer, excellent appearance, and excellent thermal fatigue resistance, effectively solving the problems of high void ratio and poor solder joint reliability of traditional solder paste.

[0004] The preparation method of the ultra-low void ratio laser solder paste of the present invention is simple, easy to operate and control, which is conducive to large-scale industrial production, and the quality of the obtained ultra-low void ratio laser solder paste is stable.

[0005] The objective of this invention is achieved through the following technical solution: an ultra-low void ratio laser solder paste, comprising the following raw materials by mass percentage: 80%–90% Sn-Ag-Cu-In alloy, 8%–10% microcapsule flux, 0.15%–0.4% rare earth additives, 0.3%–0.8% nanoporous silica, and 0.9%–2.1% modified polyamide wax.

[0006] This invention achieves a significant reduction in solder joint void ratio and a comprehensive improvement in overall performance through the synergistic compounding of Sn-Ag-Cu-In alloy, microcapsule flux, rare earth additives, nanoporous silica, and modified polyamide wax. The addition of In to the Sn-Ag-Cu-In alloy effectively reduces the melting point and surface tension of the alloy, improves the wettability of the molten solder to the substrate, and refines the grain structure of the solder joint. The microcapsule flux adopts a core-shell structure design, which enables the slow release of flux active substances during laser heating, avoiding premature volatilization or decomposition failure of the flux, ensuring sufficient flux activity throughout the welding process, effectively removing oxide film and preventing secondary oxidation. Rare earth additives can adsorb and refine oxide inclusions in the molten solder, promote the escape and discharge of bubbles, and improve the interface reaction between the solder and the substrate, forming a uniform and continuous IMC layer. Nanoporous silica has a high specific surface area and an ordered mesoporous structure, which can adsorb low-boiling-point volatiles in the solder, reduce the source of gas evolution during the welding process, and its nanoparticles are uniformly dispersed in the solder joint, playing a dispersion strengthening role and improving the mechanical properties of the solder joint. Modified polyamide wax, as a thixotropic agent, gives the solder paste excellent printability and anti-collapse properties, ensuring the regular shape of the solder joint. The synergistic effect of the components results in very few bubbles being generated in the solder paste during laser soldering, which are easily expelled, thus achieving an ultra-low void ratio. At the same time, the solder joints have a bright and full appearance, good wettability, and excellent long-term reliability.

[0007] Furthermore, the Sn-Ag-Cu-In alloy comprises the following raw materials by mass percentage: Ag 2.8%–3.2%, Cu 0.4%–0.6%, In 0.15%–0.35%, and Sn balance.

[0008] Furthermore, the Sn is composed of large-diameter Sn particles and small-diameter Sn particles mixed in a mass ratio of 6 to 8:3, wherein the large-diameter Sn particles have a particle size of 18 μm to 25 μm and the small-diameter Sn particles have a particle size of 15 μm to 18 μm; the surface of the Sn particles has an inert passivation film, and the oxygen content of the Sn is ≤80 ppm.

[0009] Furthermore, the preparation method of the Sn-Ag-Cu-In alloy includes the following steps: C1. Add Ag, Cu, In and Sn into a vacuum induction melting furnace, and evacuate to ≤10 °C. -2 After Pa, nitrogen gas is introduced to a protective atmosphere of 0.05-0.08 MPa, and the temperature is raised to 300-400℃ and held for melting. C2. Keep at 300-400℃ for 2 hours, stirring every 20-30 minutes during the period to remove the oxide slag that gradually floats to the surface of the melt. C3. The refined alloy melt from step C2 is introduced into an ultrasonic atomizing nozzle system through an intermediate ladle. Using ultrasonic vibration atomization, the melt flows through an ultrasonic vibrating disk at a steady flow rate of 0.5–2 kg / min. It is broken into tiny droplets by high-frequency ultrasonic vibration and then falls freely into a nitrogen-filled atomization tower to cool and solidify, resulting in Sn-Ag-Cu-In alloy metal powder with a particle size of 15 μm–25 μm.

[0010] In this invention, large-particle-size (18μm~25μm) and small-particle-size (15μm~18μm) Sn particles are mixed and compounded in a specific mass ratio (6~8:3), which has the following synergistic technical effects: the large-particle-size Sn particles act as a skeleton, providing good anti-collapse and printing thickness consistency, ensuring sufficient solder filling at the solder joints; the small-particle-size Sn particles fill the gaps between the large particles, increasing the Sn packing density, reducing the internal porosity of the solder joints, and at the same time, the small particles have a larger specific surface area and higher surface energy, which preferentially melts during laser heating, playing a "melt bridging" role, accelerating the melting and spreading of the overall solder, shortening the melting time, and reducing the chance of oxidation and bubble formation at high temperatures. The reasonable combination of different particle sizes also gives the solder paste system better rheological properties, which is beneficial for printing demolding and uniform solder spreading during soldering. In addition, the Sn particles have an inert passivation film on their surface and an oxygen content of ≤80ppm, which effectively reduces the oxidation of Sn during storage and use, ensuring that the flux can fully act on the clean metal surface during welding, thereby reducing the void ratio and improving wettability.

[0011] Furthermore, the rare earth additive is composed of lanthanum oxide and neodymium oxide mixed in a mass ratio of 2:1 to 4:1.

[0012] Furthermore, the nanoporous silica has a particle size of 10–50 nm and a mesopore size of 2–10 nm.

[0013] Furthermore, the microcapsule flux comprises the following raw materials by mass percentage: 55%–62% hydrogenated disproportionated rosin, 6%–9% organic acid, 22%–28% polyether polyol, 5%–8% epoxy-modified polysiloxane, 1.5%–2.5% modifier, and 0.5%–1% stabilizer.

[0014] Furthermore, the preparation method of the microcapsule flux includes the following steps: A1. Add hydrogenated disproportionated rosin and organic acid to a reactor equipped with a stirrer, add polyether polyol and stir evenly, then heat to 150-180℃ and keep stirring at this temperature until the hydrogenated disproportionated rosin is completely melted, then slowly add epoxy-modified polysiloxane and stir evenly. A2. Cool the system to 120℃, add the modifier and stabilizer in sequence, continue stirring and keeping warm for 20-40 minutes to obtain the blended melt; A3. The blended melt is microencapsulated using a centrifugal atomizing cooling tower. The molten material is sprayed into an inert gas environment in the form of tiny droplets, and then cooled and solidified to form microcapsule particles, thus obtaining microcapsule flux.

[0015] The microcapsule flux of this invention is prepared by centrifugal atomization cooling method. A blend melt containing hydrogenated disproportionated rosin, organic acid, polyether polyol, epoxy-modified polysiloxane, modifier, and stabilizer is sprayed into an inert gas environment in the form of tiny droplets, rapidly cooling and solidifying to form microcapsule particles with a core-shell structure. The epoxy-modified polysiloxane, through its epoxy groups, undergoes a cross-linking reaction with the carboxyl groups of the hydrogenated disproportionated rosin, embedding itself in the shell wall network as a functional reinforcing component, thus endowing the shell with low surface energy characteristics and high-temperature triggered rupture function. The principle and effect of this microcapsule flux are as follows: Hydrogenated disproportionated rosin, as a film-forming substance and carrier resin, melts and spreads at the welding temperature, encapsulating the solder and substrate surface, providing a reducing protective atmosphere; organic acids, as active ingredients, are slowly released from the microcapsules during the welding heating process, continuously removing oxides from the metal surface, and their decomposition products volatilize completely with minimal residue; polyether polyols, as solvents and film-forming aids, adjust the viscosity and wetting properties of the flux, while their high boiling point ensures stability during rapid laser heating; epoxy-modified polysiloxanes, as functional modifying components of the shell, have polysiloxane chains... The segments are uniformly distributed in the cross-linked network of the shell, which on the one hand endows the shell with excellent flexibility and impact resistance, making the microcapsule particles less prone to breakage during storage and printing; on the other hand, during the laser welding heating process, the polysiloxane segments in the shell migrate to the surface of the molten solder, significantly reducing the surface tension of the molten solder and improving its spreading ability. At the same time, an extremely thin protective film is formed on the surface of the solder joint, inhibiting high-temperature oxidation. The modifier can further reduce the ionic residue of the flux and enhance the bonding force between the flux and the metal interface. The stabilizer effectively prevents the flux from oxidizing and deteriorating during storage and use, extending the product's shelf life. The microcapsule structure ensures that the components do not pre-react before welding and are released sequentially according to the temperature gradient during welding, achieving a segmented fluxing effect, which greatly improves the fluxing efficiency and reduces post-weld residue, thereby helping to reduce the void rate and improve the reliability of the solder joint.

[0016] Furthermore, the polyether polyol includes at least one of diethylene glycol hexyl ether, bisphenol A polyether diol, diethylene glycol octyl ether, or tripropylene glycol ethyl ether.

[0017] Furthermore, the organic acid includes at least one selected from adipic acid, 3-methyl adipic acid, or 1,4-cyclohexanedicarboxylic acid. Preferably, the organic acid is prepared by mixing adipic acid and 3-methyl adipic acid in a mass ratio of 2:1; more preferably, the organic acid is prepared by mixing 3-methyl adipic acid and 1,4-cyclohexanedicarboxylic acid in a mass ratio of 2:1.

[0018] Furthermore, the stabilizer includes at least one of benzotriazole or an antioxidant. Preferably, the antioxidant is antioxidant 565.

[0019] Furthermore, the preparation method of the modifier includes the following steps: B1. Dissolve γ-aminopropyltrimethoxysilane and triethylamine in dichloromethane and place in an ice-water bath. Slowly pass trifluoromethanesulfonyl fluoride through the solution with stirring and react for 1-3 hours. B2. After the reaction is complete, filter to remove the triethylamine hydrofluoric acid solid generated in the reaction, and then remove the solvent by vacuum distillation to obtain the modifier.

[0020] The modifier of this invention is a silane compound containing a trifluoromethanesulfonyl amide group, prepared by reacting γ-aminopropyltrimethoxysilane with trifluoromethanesulfonyl fluoride in the presence of triethylamine as an acid-binding agent. On one hand, the trifluoromethanesulfonyl group possesses extremely strong electron-withdrawing effects and hydrophobic and oleophobic properties. Introducing this group significantly reduces the surface energy of the flux system, further improving the spreadability of the molten solder and its wettability to the substrate. On the other hand, the silane-coupled trimethoxysilane group in the modifier can undergo a condensation reaction with the silanol groups on the surface of nanoporous silica in the flux system, forming chemical bonds, enhancing the compatibility of the organic-inorganic interface, promoting the uniform dispersion of nanoporous silica in the flux, and preventing nanoparticle agglomeration, thereby fully utilizing its gas adsorption and dispersion strengthening effects. Furthermore, this modifier also has a certain complexing ability, capable of forming stable complexes with metal ions in the solder, reducing solder oxidation, and improving the density and corrosion resistance of the solder joint.

[0021] Furthermore, the molar ratio of trifluoromethanesulfonyl fluoride to γ-aminopropyltrimethoxysilane is (1.1–2):1; the molar ratio of triethylamine to γ-aminopropyltrimethoxysilane is (2–4):1.

[0022] This invention also provides a method for preparing ultra-low void ratio laser solder paste, comprising the following steps: S1. Add the microcapsule flux to a planetary vacuum mixer and stir for 5 to 10 minutes under vacuum conditions ≤ -0.095 MPa and speed of 30 to 50 r / min. Then add the modified polyamide wax and stir for 15 to 20 minutes at a temperature of 40 to 50°C and a speed of 60 to 80 r / min to obtain mixture one. S2. Add rare earth additives and nano-mesoporous silica to the above mixture one, heat to 50-60℃, stir at 80-100r / min for 30-40min, store at low temperature 1-10℃ for 22-26h, and then grind with a three-roll mill until the fineness is ≤10μm to obtain mixture two. S3. Add the ground mixture into a double planetary mixer, and then slowly add Sn-Ag-Cu-In alloy powder in 3 to 5 batches. After all the powder has been added, stir at 20 to 60 r / min under vacuum for 20 to 30 min. Then, increase the mixer speed to 50 to 80 r / min, maintain the vacuum degree ≤ -0.098 MPa, and stir at high speed for 15 to 20 min to obtain solder paste. Store at a low temperature of 1 to 10℃.

[0023] The preparation method of the ultra-low void ratio laser solder paste of the present invention is simple, easy to operate and control, which is conducive to large-scale industrial production, and the quality of the obtained ultra-low void ratio laser solder paste is stable.

[0024] The beneficial effects of this invention are as follows: (1) The ultra-low void ratio laser solder paste provided by the present invention, through the synergistic compounding of Sn-Ag-Cu-In alloy, microcapsule flux, rare earth additives, nano-mesoporous silica and modified polyamide wax, can achieve a void ratio of 2.31% after laser welding, which is far lower than the void ratio level of conventional solder paste in the prior art, effectively improving the electrical and thermal conductivity and mechanical reliability of the solder joint.

[0025] (2) The present invention uses Sn with specific particle size (large particle size 18μm~25μm and small particle size 15μm~18μm mixed at a mass ratio of 6~8:3), which improves the Sn packing density and melting uniformity. Combined with the surface treatment of the inert passivation film with ultra-low oxygen content (≤80ppm), it significantly reduces the internal porosity of the solder joint and welding spatter.

[0026] (3) The present invention introduces rare earth additives (a combination of lanthanum oxide and neodymium oxide) and nanoporous silica, which effectively adsorb and remove gases and inclusions in the solder, while refining the grains and dispersing and strengthening them, so that the solder joints have excellent thermal fatigue resistance. After 2000 cycles of high and low temperature (-40℃ to 125℃), the shear strength decay rate is only 10.3%, which is far better than the comparative example (18.6% to 23.1%), meeting the requirements of high reliability application scenarios.

[0027] (4) The preparation method of the present invention is simple, easy to operate and mild, and the solder paste obtained is of stable quality and has good batch consistency, making it suitable for large-scale industrial production. Detailed Implementation

[0028] To facilitate understanding by those skilled in the art, the present invention will be further described below with reference to embodiments. The content mentioned in the embodiments is not intended to limit the present invention.

[0029] Example 1 In this embodiment, an ultra-low void ratio laser solder paste comprises the following raw materials by mass percentage: 89% Sn-Ag-Cu-In alloy, 9.2% microcapsule flux, 0.25% rare earth additives, 0.5% nanoporous silica, and 1.05% modified polyamide wax.

[0030] In this embodiment, the modified polyamide wax used is DISPARLON 6500 from Kusumoto Chemical Co., Ltd. of Japan.

[0031] Furthermore, the Sn-Ag-Cu-In alloy comprises the following raw materials by mass percentage: Ag 3%, Cu 0.5%, In 0.2%, and Sn balance.

[0032] Furthermore, the Sn is composed of large-diameter Sn particles and small-diameter Sn particles mixed in a mass ratio of 7:3, wherein the large-diameter Sn particles have a particle size of 23 μm and the small-diameter Sn particles have a particle size of 17 μm; the surface of the Sn particles has an inert passivation film, and the oxygen content of the Sn is ≤80 ppm.

[0033] Furthermore, the preparation method of the Sn-Ag-Cu-In alloy includes the following steps: C1. Add Ag, Cu, In and Sn into a vacuum induction melting furnace, and evacuate to ≤10 °C. -2 After Pa, nitrogen gas is introduced to a protective atmosphere of 0.06 MPa, and the temperature is raised to 350°C and held for melting. C2. Keep at 350℃ for 2 hours, stirring every 25 minutes during the process, to remove the oxide slag that gradually floats to the surface of the melt. C3. The refined alloy melt from step C2 is introduced into an ultrasonic atomizing nozzle system through an intermediate ladle. Using ultrasonic vibration atomization, the melt flows through an ultrasonic vibrating disk at a steady flow rate of 1.5 kg / min. It is broken into tiny droplets by high-frequency ultrasonic vibration and then falls freely into a nitrogen-filled atomization tower to cool and solidify, resulting in Sn-Ag-Cu-In alloy metal powder with a particle size of 15 μm to 20 μm.

[0034] Furthermore, the rare earth additive is composed of lanthanum oxide and neodymium oxide mixed in a mass ratio of 3:1.

[0035] Furthermore, the nanoporous silica has a particle size of 20–30 nm and a mesopore size of 4–6 nm.

[0036] Furthermore, the microcapsule flux comprises the following raw materials by mass percentage: 58% hydrogenated disproportionated rosin, 8% organic acid, 25% polyether polyol, 6% epoxy-modified polysiloxane, 2% modifier, and 1% stabilizer.

[0037] In this embodiment, the epoxy-modified polysiloxane is Shin-Etsu X-22-163 from Japan. The hydrogenated disproportionated rosin is Arakawa KE-311.

[0038] Furthermore, the preparation method of the microcapsule flux includes the following steps: A1. Add hydrogenated disproportionated rosin and organic acid to a reactor equipped with a stirrer, add polyether polyol and stir evenly, then heat to 160°C and keep stirring at this temperature until the hydrogenated disproportionated rosin is completely melted. Then slowly add epoxy-modified polysiloxane and stir evenly. A2. Cool the system to 120℃, add the modifier and stabilizer in sequence, continue stirring and keep warm for 30 minutes to obtain the blended melt; A3. The blended melt is microencapsulated using a centrifugal atomizing cooling tower. The molten material is sprayed into an inert gas environment in the form of tiny droplets, cooled and solidified to form microcapsule particles, which are then sieved to obtain microcapsule flux.

[0039] Furthermore, the polyether polyol is diethylene glycol hexyl ether.

[0040] Furthermore, the organic acid is a mixture of adipic acid and 3-methyladipic acid in a mass ratio of 2:1.

[0041] Furthermore, the stabilizer is antioxidant 565.

[0042] Furthermore, the preparation method of the modifier includes the following steps: B1. Dissolve γ-aminopropyltrimethoxysilane and triethylamine in dichloromethane and place in an ice-water bath. Slowly pass trifluoromethanesulfonyl fluoride through the solution with stirring and react for 2 hours. B2. After the reaction is complete, filter to remove the triethylamine hydrofluoric acid solid generated in the reaction, and then remove the solvent by vacuum distillation to obtain the modifier.

[0043] Furthermore, the molar ratio of trifluoromethanesulfonyl fluoride to γ-aminopropyltrimethoxysilane is 1.5:1; the molar ratio of triethylamine to γ-aminopropyltrimethoxysilane is 3:1.

[0044] This embodiment also provides a method for preparing ultra-low void ratio laser solder paste, including the following steps: S1. Add the microcapsule flux to a planetary vacuum mixer and stir for 8 minutes under vacuum degree ≤ -0.095MPa and speed of 40r / min. Then add the modified polyamide wax and stir for 18 minutes at a temperature of 45℃ and a speed of 70r / min to obtain mixture one. S2. Add rare earth additives and nano-mesoporous silica to the above mixture one, heat to 55°C, stir at 90r / min for 35min, store at low temperature 5°C for 24h, and then grind with a three-roll mill until the fineness is ≤10μm to obtain mixture two. S3. Add the ground mixture into a double planetary mixer, and then slowly add Sn-Ag-Cu-In alloy powder in 4 batches. After all the powder is added, stir at 40 r / min under vacuum for 25 min. Then increase the mixer speed to 65 r / min, maintain the vacuum degree ≤-0.098 MPa, and stir at high speed for 18 min to obtain solder paste. Store at low temperature 5℃.

[0045] Comparative Example 1 Unlike Example 1, this comparative example uses an equal amount of hydrogenated disproportionated rosin to replace the epoxy-modified polysiloxane.

[0046] Comparative Example 2 Unlike Example 1, this comparative example uses an equal amount of hydrogenated disproportionated rosin to replace the modifier.

[0047] Comparative Example 3 Unlike Example 1, the Sn used in this comparative example is a Sn block with an inert passivation film on its surface and an oxygen content ≤80ppm.

[0048] Performance testing The performance of the ultra-low void ratio laser solder pastes prepared in Example 1 and Comparative Examples 1-3 was tested. The void ratio of the solder joints after laser soldering, the thickness of the IMC layer, the appearance inspection, and the shear strength attenuation rate after high and low temperature cycling were tested. The results are shown in Table 1.

[0049] The laser welding parameters include: peak power 60W, spot diameter 1.5mm, preheating temperature 160℃, peak temperature 260℃, and laser welding on oxygen-free copper.

[0050] Table 1

[0051] in, (1) Visual inspection: Using an optical stereo microscope (magnification 100×), and referring to the IPC-A-610 standard, observe the surface gloss of the solder joint, solder ball splashes and pinhole defects.

[0052] (2) Void rate detection: Using an X-Ray non-destructive testing instrument (equipment resolution ≥ 5 μm), and referring to the IPC-7095A standard, the projected area of ​​the solder joint and the void area are analyzed by image analysis, and the void rate is calculated as (total void area / total projected area of ​​solder joint) × 100%. Five solder joints are measured in each group and the average value is taken.

[0053] (3) Detection of shear strength attenuation rate after high and low temperature cycling: Temperature cycling conditions: low temperature section -40℃ for 30min, high temperature section 125℃ for 30min, heating and cooling rate 10℃ / min, single cycle period 70min, 500, 1000 and 2000 temperature cycles were completed respectively, and the shear strength of the weld joint was tested according to JIS Z 3198-6 standard. Attenuation rate = [(initial average shear strength - average shear strength after cycling) / initial average shear strength] × 100%, number of samples per group n = 5.

[0054] The above embodiments are preferred implementations of the present invention. In addition, the present invention can be implemented in other ways. Any obvious substitutions without departing from the concept of the present invention are within the protection scope of the present invention.

Claims

1. A laser solder paste with ultra-low void ratio, characterized in that: It includes the following raw materials by mass percentage: 80%–90% Sn-Ag-Cu-In alloy, 8%–10% microcapsule flux, 0.15%–0.4% rare earth additives, 0.3%–0.8% nano-mesoporous silica, and 0.9%–2.1% modified polyamide wax.

2. The ultra-low void ratio laser solder paste according to claim 1, characterized in that: The Sn-Ag-Cu-In alloy comprises the following raw materials by mass percentage: Ag 2.8%–3.2%, Cu 0.4%–0.6%, In 0.15%–0.35%, and Sn balance.

3. The ultra-low void ratio laser solder paste according to claim 2, characterized in that: The Sn is composed of large-diameter Sn particles and small-diameter Sn particles mixed in a mass ratio of 6 to 8:

3. The large-diameter Sn particles have a particle size of 18 μm to 25 μm, and the small-diameter Sn particles have a particle size of 15 μm to 18 μm. The surface of the Sn particles has an inert passivation film, and the oxygen content of the Sn is ≤80 ppm.

4. The ultra-low void ratio laser solder paste according to claim 1, characterized in that: The microcapsule flux comprises the following raw materials by mass percentage: 55%–62% hydrogenated disproportionated rosin, 6%–9% organic acid, 22%–28% polyether polyol, 5%–8% epoxy-modified polysiloxane, 1.5%–2.5% modifier, and 0.5%–1% stabilizer.

5. The ultra-low void ratio laser solder paste according to claim 4, characterized in that: The preparation method of the microcapsule flux includes the following steps: A1. Add hydrogenated disproportionated rosin and organic acid to a reactor equipped with a stirrer, add polyether polyol and stir evenly, then heat to 150-180℃ and keep stirring at this temperature until the hydrogenated disproportionated rosin is completely melted, then slowly add epoxy-modified polysiloxane and stir evenly. A2. Cool the system to 120℃, add the modifier and stabilizer in sequence, continue stirring and keep warm for 20-40 minutes to obtain the blended melt; A3. The blended melt is microencapsulated using a centrifugal atomizing cooling tower. The molten material is sprayed into an inert gas environment in the form of tiny droplets, and then cooled and solidified to form microcapsule particles, thus obtaining microcapsule flux.

6. The ultra-low void ratio laser solder paste according to claim 4, characterized in that: The organic acid includes at least one of adipic acid, 3-methyl adipic acid, or 1,4-cyclohexanedicarboxylic acid.

7. The ultra-low void ratio laser solder paste according to claim 4, characterized in that: The stabilizer includes at least one of benzotriazole or an antioxidant.

8. The ultra-low void ratio laser solder paste according to claim 1, characterized in that: The rare earth additive is a mixture of lanthanum oxide and neodymium oxide in a mass ratio of 2:1 to 4:

1.

9. The ultra-low void ratio laser solder paste according to claim 4, characterized in that: The preparation method of the modifier includes the following steps: B1. Dissolve γ-aminopropyltrimethoxysilane and triethylamine in dichloromethane and place in an ice-water bath. Slowly pass trifluoromethanesulfonyl fluoride through the solution with stirring and react for 1-3 hours. B2. After the reaction is complete, filter to remove the triethylamine hydrofluoric acid solid generated in the reaction, and then remove the solvent by vacuum distillation to obtain the modifier.

10. A method for preparing an ultra-low void ratio laser solder paste according to any one of claims 1-9, characterized in that: Includes the following steps: S1. Add the microcapsule flux to a vacuum mixer and stir for 5 to 10 minutes under vacuum conditions ≤ -0.095 MPa and speed of 30 to 50 r / min. Then add the modified polyamide wax and heat to 40 to 50℃ and stir for 15 to 20 minutes at a speed of 60 to 80 r / min to obtain mixture one. S2. Add rare earth additives and nano-mesoporous silica to the above mixture one, heat to 50-60℃, stir at 80-100r / min for 30-40min, store at low temperature 1-10℃ for 22-26h, and then grind with a three-roll mill until the fineness is ≤10μm to obtain mixture two. S3. Add the ground mixture into a double planetary mixer, and then slowly add Sn-Ag-Cu-In alloy powder in 3 to 5 batches. After all the powder has been added, stir at 20 to 60 r / min under vacuum for 20 to 30 min. Then, increase the mixer speed to 50 to 80 r / min, maintain the vacuum degree ≤ -0.098 MPa, and stir at high speed for 15 to 20 min to obtain solder paste. Store at a low temperature of 1 to 10℃.

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