Preparation method of surface passivated solder powder double-latent no-clean halogen-free tin paste

Abstract

The application discloses a preparation method of surface passivated solder powder non-washing halogen-free tin paste, relates to the technical field of electronic assembly materials, and takes SAC305 type 5 clean solder powder as the main body, sprays a pyrolyzable composite passivation layer composed of 3-glycidyloxypropyltrimethoxysilane pre-hydrolysis oligomer, 2-ethylhexyl acid phosphonate and hydrogenated rosin acid / decanedioic acid mono-2-hydroxyethyl ester complex under the condition of nitrogen, mixes the vacuum dried pyrolyzable composite passivation layer with double-latent halogen-free flux, and obtains the tin paste through low shear pre-wetting, high shear dispersion, step vacuum degassing and low temperature curing. The method controls the solder powder interface isolation, the active component release in sections and the mixing shear window, inhibits the early reaction between the solder powder oxidation film and the active component during the storage and the steel net staying, and improves the rheological stability, the printing consistency, the reflow combination stability and the post-soldering electrical reliability of the tin paste.

Description

Technical Field

[0001] This invention relates to the field of electronic assembly materials technology, specifically to a method for preparing surface passivated solder powder no-clean halogen-free solder paste. Background Technology

[0002] In surface mount electronics manufacturing, SAC305 Type 5 no-clean halogen-free solder paste is commonly used for stencil printing and reflow soldering of 01005 chips, narrow-pitch chips, power modules, and bottom terminal devices. Since solder paste is typically obtained by mixing solder powder with a flux carrier, the particle size of the solder powder directly affects the release process of the printing openings, the uniformity of the vias, and the solder joint merging process. With the reduction in device solder tip size, narrowing of stencil openings, and the use of no-clean processes on high-density boards, finer solder powder is more convenient to deposit through smaller openings. However, this increases its specific surface area, and its surface SnO / SnO2 oxide film coexists for a long time with organic acids, amine salts, wetting agents, and thixotropic systems in the rosin / resin system.

[0003] Most existing no-clean halogen-free solder pastes are formulated around alloy powder, rosin-based flux, organic acid activators, thixotropic agents, and corrosion inhibitors. Some technologies focus on surface protection or phased release of activators. While these technologies can meet general soldering needs, the simultaneous presence of Type 5 solder powder, high metal content, long-term storage, stencil exposure, and air reflow can lead to slow acid-base association between the oxide film on the solder powder surface and the active components, the formation of metal carboxylates, oxide film rearrangement, and interfacial adsorption imbalance. This process alters the ratio of free active components to resin / solvent / thixotropic network in the continuous phase of the paste, causing shifts in viscosity, yield stress, and thixotropic recovery. During the printing stage, issues arise such as reduced transfer efficiency, clogging of fine openings, pattern edge collapse, or scraper adhesion. During the reflow stage, problems include improper pre-melting film removal timing, delayed solder powder particle merging, uneven local residual volatilization, and limited gas exhaust from large pads, increasing the risk of unmerged 01005 pattern resembling grapes, voids in bottom terminal devices, solder balls, and residual ion migration under humid bias conditions. These problems are not simply caused by insufficient activity of a certain flux or improper mixing parameters, but rather by process issues resulting from the coupling of the surface chemistry of fine-particle solder powder, the potential reactivity of no-clean halogen-free flux, and the continuous operation of storage-printing-reflow.

[0004] Therefore, the current technical problem is: when fine-particle SAC305 Type 5 no-clean halogen-free solder paste is used for high-density surface mount soldering, the interface reaction imbalance occurs due to the premature reaction between the solder powder oxide film and the active components of the flux during storage, stencil dwell and reflow heating, and this imbalance causes fluctuations in the overall window of operation under long-term continuous conditions. Summary of the Invention

[0005] (a) Technical problems to be solved To address the shortcomings of existing technologies, this invention provides a method for preparing a surface passivated solder powder no-clean halogen-free solder paste. The method uses SAC305 Type 5 clean solder powder as the main component, which is spray-coated under nitrogen conditions with a thermally degradable composite passivation layer composed of a pre-hydrolyzed oligomer of 3-glycidyl etheroxypropyltrimethoxysilane, 2-ethylhexyl acid phosphate, and a hydrogenated rosin acid / sebic acid mono-2-hydroxyethyl ester complex. After vacuum drying, it is mixed with a dual-latency halogen-free flux and subjected to low-shear pre-wetting, high-shear dispersion, stepped vacuum degassing, and low-temperature curing to obtain the solder paste. This method, through solder powder interface isolation, segmented release of flux activity, and control of the mixing shear window, inhibits premature reaction between the solder powder oxide film and active components during storage and stencil dwell time; thus solving the technical problems described in the background art.

[0006] (II) Technical Solution To achieve the above objectives, the present invention provides the following technical solution: A method for preparing surface passivated solder powder no-clean halogen-free solder paste includes: spraying SAC305 Type 5 clean solder powder under nitrogen to form a thermally degradable composite passivation layer composed of 3-glycidyl etheroxypropyltrimethoxysilane pre-hydrolyzed oligomer, 2-ethylhexyl acid phosphate, and hydrogenated rosin acid / sebacic acid mono-2-hydroxyethyl ester complex; and vacuum drying to obtain 880–890 parts by weight of surface passivated solder paste. The powder was then combined with a double-latent halogen-free flux containing succinic acid / N,N-diisopropylethanolamine salt, glutaric acid / 2-methylimidazolium salt, dodecenylsuccinic anhydride-rosin alcohol half ester, and sebacic acid mono-2-hydroxyethyl ester / tributylamine salt to make up to 1000 parts by weight. The mixture was then subjected to low-shear pre-wetting, high-shear dispersion with a cumulative equivalent shear of 6.0×10^4–9.0×10^4, step-vacuum degassing, and curing at 3–8°C for 24–36 hours to obtain solder paste.

[0007] Furthermore, the pyrolytic composite passivation layer comprises, based on 1000 parts by weight of the final solder paste, 0.05–0.08 parts by weight of 3-glycidyl etheroxypropyltrimethoxysilane pre-hydrolyzed oligomer, 0.02–0.04 parts by weight of 2-ethylhexyl acid phosphate, and 0.08–0.12 parts by weight of hydrogenated rosin acid / sebacic acid mono-2-hydroxyethyl ester composite; in the hydrogenated rosin acid / sebacic acid mono-2-hydroxyethyl ester composite, the mass ratio of hydrogenated rosin acid to sebacic acid mono-2-hydroxyethyl ester is 1.5:1–2.5:1; the solid content of the pyrolytic composite passivation layer is 0.012–0.050% by weight based on the mass of SAC305 Type 5 net solder powder.

[0008] Furthermore, the passivation solution used for spray coating is prepared based on 1000 parts by weight of the final solder paste, consisting of 40–45 parts by weight of anhydrous isopropyl acetate, 16–20 parts by weight of n-heptane, 0.05–0.08 parts by weight of 3-glycidyl etheroxypropyltrimethoxysilane, 0.0055–0.0101 parts by weight of deionized water, 0.001–0.003 parts by weight of glacial acetic acid, 0.02–0.04 parts by weight of 2-ethylhexyl acid phosphate, and 0.08–0.12 parts by weight of hydrogenated rosin acid / sebaceous acid mono-2-hydroxyethyl ester complex, with a water / silicon molar ratio of 1.45–1.65; The passivation solution is pre-hydrolyzed at 20–25°C for 15–25 minutes, then 2-ethylhexyl acid phosphate and hydrogenated rosin acid / sebacic acid mono-2-hydroxyethyl ester complex are added and stirring is continued for 10–15 minutes; the spraying rate is 0.70–0.78 parts by mass / min and the spraying time is 75–85 minutes; after spraying, dry mixing is carried out for 20–30 minutes, and then step vacuum drying is performed at 32–38°C.

[0009] Furthermore, the alloy composition of the SAC305 Type 5 solder powder, by mass percentage, is 2.8–3.2% silver, 0.4–0.6% copper, and the balance tin; the D10, D50, and D90 particle sizes of the SAC305 Type 5 solder powder are 10–14 μm, 17–23 μm, and 25–32 μm, respectively; the specific surface area is 0.045–0.060 m² / g; the total oxygen content of the powder is 400–650 ppm; the thickness of the primary oxide film is 2.5–3.8 nm; the SnO / SnO2 peak area ratio measured by X-ray photoelectron spectroscopy is 0.70–1.20; and the sphericity is not less than 0.94.

[0010] Furthermore, the dual-latent halogen-free flux comprises, by weight, 26.0–30.0 parts of hydrogenated rosin glycerol ester with an acid value of 8–12 mgKOH / g; 10.5–13.5 parts of polymerized rosin with a softening point of 110–125℃; 4.5–6.5 parts of terpene phenolic resin with a hydroxyl value of 45–65 mgKOH / g; 3.3–4.8 parts of low-acid-value acrylic resin with a glass transition temperature of 48–56℃; and 5 parts of tetrahydrofurfuryl alcohol. 8–7.2 parts by weight; 6.5–8.0 parts by weight of dipropylene glycol monomethyl ether; 10.0–12.2 parts by weight of diethylene glycol monobutyl ether; 7.0–8.5 parts by weight of propylene glycol phenyl ether; 1.6–2.2 parts by weight of succinic acid / N,N-diisopropylethanolamine salt; 1.3–2.0 parts by weight of glutaric acid / 2-methylimidazolium salt; 2.8–3.8 parts by weight of dodecenylsuccinic anhydride-rosin alcohol half ester; 2.1–3.0 parts by weight of sebacic acid mono-2-hydroxyethyl ester / tributylamine salt.

[0011] Furthermore, the dual-latency halogen-free flux further includes: hydrogenated castor oil micro powder with a D90 particle size of 5–10 μm, in a concentration of 3.5–4.8 parts by weight; polyamide wax micro powder with a D90 particle size of 5–10 μm, in a concentration of 1.8–2.8 parts by weight; benzotriazole 0.20–0.45 parts by weight; methylbenzotriazole 0.15–0.35 parts by weight; hindered phenolic antioxidant 0.45–0.80 parts by weight; triphenyl phosphite 0.15–0.40 parts by weight; polyether-modified polysiloxane 0.25–0.55 parts by weight; acetylenic diol nonionic wetting agent 0.15–0.35 parts by weight; low-foaming polyether leveling agent 0.08–0.25 parts by weight; hindered tertiary amine proton scavenger 0.35–0.65 parts by weight; and non-silicone polyether defoamer 0.15–0.40 parts by weight.

[0012] Furthermore, the acid / amine molar ratio of the succinic acid / N,N-diisopropylethanolamine salt is 1.00:0.95–1.00:1.10, and the acid / base molar ratio of the glutaric acid / 2-methylimidazolium salt is 1.00:0.85–1.00:1.05. The water content of both salts is not higher than 0.15% by mass, the D90 is not greater than 12 μm, the differential scanning calorimetry main thermal transition peak is at 130–150 °C, and the initial free acid proportion (based on total acid) is not higher than 18%. The dodecenyl succinic anhydride-rosin alcohol half ester has an acid value of 70–115 mg KOH / g and residual anhydride groups not exceeding 6.0% by mass; the sebacic acid mono-2-hydroxyethyl ester / tributylamine salt has an acid / amine molar ratio of 1.00:0.95–1.00:1.10, a differential scanning calorimetry main thermal transition or dissociation peak of 185–205℃, a moisture content of not exceeding 0.12% by mass at 25℃, and an insoluble matter content of not exceeding 0.05% by mass after filtration.

[0013] Furthermore, the preparation of the dual-latent halogen-free flux includes: heating tetrahydrofurfuryl alcohol, dipropylene glycol monomethyl ether, diethylene glycol monobutyl ether, and propylene glycol phenyl ether to 130–138°C under a slight positive pressure of nitrogen; adding hydrogenated rosin glycerol ester at 65–75°C; adding polymerized rosin at 88–96°C; adding terpene phenolic resin and low-acid-value acrylic resin at 112–122°C and holding for 25–35 minutes; lowering the temperature to 84–88°C and adding dodecenyl succinic anhydride-rosin alcohol half ester and sebacic acid mono-2-hydroxyethyl ester / tributylamine salt; and lowering the temperature to 70–70°C. Add succinic acid / N,N-diisopropylethanolamine salt and glutaric acid / 2-methylimidazolium salt at 4℃, then add benzotriazole, methylbenzotriazole, hindered phenolic antioxidant, triphenyl phosphite, polyether-modified polysiloxane, acetylenol nonionic wetting agent, low-foaming polyether leveling agent, hindered tertiary amine proton scavenger and non-silicone polyether defoamer at 60–65℃, then add hydrogenated castor oil powder and polyamide wax powder at 52–56℃ and shear for 60–80 minutes. After that, grind twice with three rollers and degas for 12–20 minutes under 8–12 kPa absolute pressure.

[0014] Furthermore, during solder paste mixing, the oxygen content in the mixing chamber is no higher than 300 ppm, and the dew point is lower than -45°C; the low-shear pre-wetting includes spreading all the double-latent halogen-free flux at the bottom of the mixing cup, adding surface-passivated solder powder at an equivalent shear rate of 12–18 s⁻¹ at 35–45 parts by mass / min, adding powder for 20–24 minutes, and continuing low-shear pre-wetting for 5–8 minutes; the equivalent shear rate of the high-shear dispersion is 120–150 s⁻¹, lasting for 8–10 minutes, with a cumulative equivalent shear amount of 6.0 × 10^4–9.0 × 10^4, and the paste temperature is no higher than 24–26°C.

[0015] Furthermore, the stepped vacuum degassing includes reducing the equivalent shear rate to 10–15 s⁻¹ and applying vacuum in steps of absolute pressure: 25–35 kPa for 2–4 minutes, 15–20 kPa for 4–6 minutes, and 8–12 kPa for 6–10 minutes. After degassing, the pressure is returned to atmospheric pressure with dry nitrogen over 1.5–3.0 minutes. The mixed solder paste is then transferred to a light-proof sealed container, and the headspace inside the container is replaced with dry nitrogen 2–4 times. Finally, it is cured at 3–8°C for 24–36 hours.

[0016] (III) Beneficial Effects This invention provides a method for preparing surface passivated solder powder no-clean halogen-free solder paste, which has the following beneficial effects: By configuring the surface-passivated SAC305 Type 5 solder powder, dual-latent halogen-free flux, and three-stage vacuum mixing and curing steps as a continuous process chain, the interfacial reaction sequence of the solder paste during storage, stencil dwell, and reflow heating stages is made more stable. A pyrolytic composite passivation layer is pre-formed on the solder powder surface, which helps reduce the chance of direct contact between the solder powder's native oxide film and the active components of the flux, thus reducing interference with the rheological state of the paste during storage caused by acid-base association and the formation of metal carboxylates.

[0017] The dual-latency halogen-free flux employs a low-temperature latent activator and a high-temperature latent activator to satisfy the two activation stages before and after preheating and melting, ensuring that the flux activity is released early without concentration and guaranteeing the merging window of fine-particle solder powder. A three-stage mixing method is used for pre-wetting with low-shear and controlled high-shear dispersion, and a stepped vacuum degassing method is used to maintain uniform solder powder wetting, intact passivation interface, and removal of paste microbubbles, avoiding excessive shearing that damages the surface passivation layer. This achieves the goal of improving the storage stability, printing consistency, reflow merging stability, and post-soldering electrical reliability of no-clean halogen-free solder paste in high-density surface mount technology. The above improvements are attributed to the synergistic effect between the solder powder interface, flux release sequence, and mixing shear window. Attached Figure Description

[0018] Figure 1This is a schematic diagram of the overall preparation process of the high wetting stability no-clean halogen-free solder paste of the present invention; Figure 2 This is a schematic diagram of the interface structure of the composite passivation layer on the surface of the welding powder particles of the present invention; Figure 3 This is a schematic diagram of the welding powder surface passivation treatment equipment and spray drying process of the present invention; Figure 4 This is a schematic diagram of the component modules and step-by-step preparation process of the dual-latency halogen-free flux of the present invention; Figure 5 This is a schematic diagram illustrating the matching of the dual latent release, segmented volatilization, and reflux temperature windows of the present invention. Figure 6 This is a schematic diagram of the three-stage vacuum mixing process of the present invention; Figure 7 This is a schematic diagram comparing the complete collaborative system and failure mechanism of the present invention. Detailed Implementation

[0019] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0020] Please see Figures 1-7 This invention provides a method for preparing surface passivated solder powder no-clean halogen-free solder paste, comprising: The following embodiments illustrate the preparation method of the present invention and the detectable technical characteristics of the obtained solder paste. Unless otherwise stated, all parts and percentages in this embodiment are by mass; the amount of raw materials fed is based on 1000 parts by mass of the final solder paste, and the amount of sample taken for testing can still be expressed in grams or milliliters; the temperature is the actual measured temperature of the material; the pressure in the vacuum drying and vacuum degassing steps is absolute pressure, and the nitrogen micro-positive pressure, nitrogen filling pressure and reactor pressure control values ​​are all gauge pressure or pressure difference relative to atmospheric pressure; the lead-free solder powder is SAC305 type 5 solder powder. Example 1: Preparation of solder paste with high wetting stability 1.1 Preparation Objectives and Raw Material Range

[0021] A high-wetting-stability no-clean halogen-free solder paste was prepared based on a final solder paste volume of 1000 parts by weight. The solder paste comprises surface-passivated SAC305 Type 5 solder powder and dual-latent halogen-free flux, totaling 1000 parts by weight; wherein the surface-passivated SAC305 Type 5 solder powder comprises 880–890 parts by weight, and the dual-latent halogen-free flux is the balance to bring the total to 1000 parts by weight. Preferably, the surface-passivated solder powder comprises 883.65–884.74 parts by weight, of which 883.5–884.5 parts by weight are net SAC305 alloy solder powder, and 0.15–0.24 parts by weight are pyrolytic composite passivation layer solids; the amounts of each component can be normalized according to the final solder paste volume.

[0022] The alloy composition of the lead-free solder powder is as follows: tin is in the balance, silver is 2.8–3.2% by mass, and copper is 0.4–0.6% by mass; the solder powder type is Type 5, or Type 4.5 to Type 5 solder powder with a corresponding particle size range; the particle sizes of D10, D50, and D90 are 10–14 μm, 17–23 μm, and 25–32 μm, respectively; the specific surface area is 0.045–0.060 m² / g; the total oxygen content of the powder is 400–650 ppm; the thickness of the primary oxide film is 2.5–3.8 nm; the SnO / SnO2 peak area ratio measured by X-ray photoelectron spectroscopy is 0.70–1.20; and the sphericity is not less than 0.94.

[0023] Sphericity can be obtained through scanning electron microscope image analysis; the thickness of the primary oxide film can be determined by X-ray photoelectron spectroscopy depth ablation, transmission electron microscope cross-section, or a combination of both.

[0024] 1.1A Example 1-A: Determining the formulation and single-point process parameters corresponding to experimental data Example 1 is a preferred embodiment of the present invention; to ensure a definite correspondence between the core experimental data in Tables 1 and 2, the single-point formulation and single-point process parameters of Example 1-A are further provided. Example 1-A uses a final solder paste total of 1000,000 parts by mass as a baseline, and all feed amounts, temperatures, times, pressures, and shearing amounts are fixed values.

[0025] In Example 1-A, the final solder paste was based on 1000,000 parts by weight, of which 883,820 parts by weight were SAC305 Type 5 net solder powder with D10, D50 and D90 particle sizes of 12.4 μm, 20.1 μm and 28.6 μm, respectively, and a specific surface area of ​​0.0520 m² / g; 0.180 parts by weight were thermally degradable composite passivation layer solid, and 0.060 parts by weight were composed of silane pre-hydrolyzed oligomers. It consists of 0.029 parts by weight of acidic phosphate ester and 0.091 parts by weight of hydrogenated rosin acid / sebacic acid monoester complex; the dual-latent halogen-free flux is 116.000 parts by weight, and its internal components are normalized to 100.000 parts by weight of flux; the total of the above components is 1000.000 parts by weight, corresponding to a net alloy powder content of 88.382% by weight and a surface passivated solder powder content of 88.400% by weight.

[0026] In Example 1-A, the formula for the dual-latent halogen-free flux, based on 100,000 parts by mass, is as follows; when actually preparing 116,000 parts by mass of flux, the scale is increased proportionally.

[0027] The resin / film-forming subsystem includes: hydrogenated rosin glycerol ester, with an acid value of 10.0 mgKOH / g, comprising 27.716 parts by weight; polymerized rosin, with a softening point of 118.0℃, comprising 12.112 parts by weight; terpene phenolic resin, with a hydroxyl value of 55.0 mgKOH / g, comprising 5.129 parts by weight; and low acid value acrylic resin, with a glass transition temperature of 52.0℃, comprising 3.922 parts by weight.

[0028] The solvogenetic system includes: 6.552 parts by mass of tetrahydrofurfuryl alcohol, 7.241 parts by mass of dipropylene glycol monomethyl ether, 11.034 parts by mass of diethylene glycol monobutyl ether, and 7.672 parts by mass of propylene glycol phenyl ether.

[0029] The low-temperature latent activator comprises: 1.897 parts by weight of succinic acid / N,N-diisopropylethanolamine salt and 1.638 parts by weight of glutaric acid / 2-methylimidazolium salt.

[0030] The high-temperature latent activator II comprises: 3.276 parts by weight of dodecenyl succinic anhydride-rosin alcohol half ester and 2.500 parts by weight of sebacic acid mono-2-hydroxyethyl ester / tributylamine salt.

[0031] The thixotropic system includes: hydrogenated castor oil micro powder with a D90 particle size of 7.5 μm, comprising 4.138 parts by mass; and polyamide wax micro powder with a D90 particle size of 6.8 μm, comprising 2.328 parts by mass.

[0032] The corrosion inhibitor / antioxidant subsystem includes: 0.302 parts by mass of benzotriazole, 0.216 parts by mass of methylbenzotriazole, 0.603 parts by mass of hindered phenolic antioxidant, and 0.259 parts by mass of triphenyl phosphite.

[0033] The non-fluorinated wetting / defoaming system includes: 0.388 parts by weight of polyether-modified polysiloxane, 0.216 parts by weight of acetylenic diol nonionic wetting agent, and 0.129 parts by weight of low-foaming polyether leveling agent.

[0034] The post-weld acid fixative includes 0.474 parts by weight of hindered tertiary amine proton scavenger.

[0035] Vacuum defoaming aids include: 0.258 parts by weight of non-silicone polyether defoamer.

[0036] The key single-point process parameters of Example 1-A are as follows: 42,000 parts by mass of isopropyl acetate, 18,000 parts by mass of n-heptane, 0.060 parts by mass of 3-glycidyl etheroxypropyltrimethoxysilane, 0.0068 parts by mass of deionized water, 0.0018 parts by mass of glacial acetic acid, 0.029 parts by mass of 2-ethylhexyl acid phosphate, and 0.091 parts by mass of hydrogenated rosin acid / sebaceous acid mono-2-hydroxyethyl ester complex; the passivation solution is pre-hydrolyzed at 22.5°C for 20.0 minutes, the spray rate is 0.740 parts by mass / minute, and the spray time is 81.3 minutes. In the solder paste mixing process, the first stage had an equivalent shear rate of 15.0 s⁻¹, a powder feeding rate of 40.18 parts by mass / min, and a powder feeding time of 22.0 minutes; the second stage had an equivalent shear rate of 135.0 s⁻¹, lasting for 9.0 minutes, with a cumulative equivalent shear amount of 7.29 × 10⁻¹. 4 The third stage involves degassing at absolute pressures of 30.0 kPa, 18.0 kPa, and 10.0 kPa; the low-temperature curing conditions are 5.0℃ for 30.0 h. 1.2 The surface of the solder powder can be thermally passivated.

[0037] Based on a final solder paste total of 1000 parts by mass, the passivation layer solid consists of 0.05–0.08 parts by mass of 3-glycidyl etheroxypropyltrimethoxysilane pre-hydrolyzed oligomer, 0.02–0.04 parts by mass of 2-ethylhexyl acid phosphate, and 0.08–0.12 parts by mass of hydrogenated rosin acid / sebacic acid mono-2-hydroxyethyl ester complex, totaling 0.15–0.24 parts by mass. In the hydrogenated rosin acid / sebacic acid mono-2-hydroxyethyl ester complex, the mass ratio of hydrogenated rosin acid to sebacic acid mono-2-hydroxyethyl ester is 1.5:1–2.5:1, preferably 2.0:1. Based on the net solder powder mass, the passivation layer solid content is 0.012–0.050% by mass, and the target equivalent passivation layer thickness is 1.8–6.5 nm, preferably 3.2–3.5 nm.

[0038] It adopts a 1.0–2.0L inert atmosphere horizontal paddle powder mixer with a jacket, with no dead corner powder collection tank at the bottom of the reactor, the gap between the outer edge of the paddle and the cylinder wall is 1.0–1.5mm, the inner wall is polished to Ra≤0.4μm, and is equipped with a grounded anti-static system, an online oxygen content probe, a dew point meter, a two-fluid nitrogen atomizing nozzle and a condensation recovery bottle.

[0039] Before using the equipment, purge with dry nitrogen 4–6 times, each time purging to 0.10–0.15 MPa (gauge pressure) and then releasing to atmospheric pressure, ultimately maintaining a slight positive nitrogen pressure of 3–8 kPa (gauge pressure). When the oxygen content is below 500 ppm and the dew point is below -45°C, add 883.5–884.5 parts by weight of SAC305 Type 5 clean solder powder.

[0040] In this step, isopropyl acetate, n-heptane, etc., are process solvents used for passivation treatment of solder powder surface. They are removed or recovered in the subsequent vacuum drying step and are not included in the 1000 parts by mass composition of the final solder paste.

[0041] In a brown glass bottle with a volume of not less than 120 mL, preferably 120–150 mL, add 40–45 parts by weight of anhydrous isopropyl acetate and 16–20 parts by weight of n-heptane. Stir at 20–25 °C and 400–500 rpm. Then, add 0.05–0.08 parts by weight of 3-glycidoxypropyltrimethoxysilane, deionized water, and 0.001–0.003 parts by weight of glacial acetic acid. The amount of deionized water is adjusted according to the molar amount of 3-glycidoxypropyltrimethoxysilane to maintain a water / silicon molar ratio of 1.45–1.65. Based on the amount of silane used (0.05–0.08 parts by weight), the amount of deionized water is approximately 0.0055–0.0101 parts by weight. This water / silicon molar ratio is used to form partially hydrolyzed silanol oligomers, avoiding complete hydrolysis and gelation. The system should remain transparent, with slight refractive enhancement permissible, but should not exhibit milky turbidity or visible colloidal particles. After pre-hydrolysis for 15–25 minutes, add 0.02–0.04 parts by weight of 2-ethylhexyl acid phosphate and 0.08–0.12 parts by weight of hydrogenated rosin acid / sebaceous acid mono-2-hydroxyethyl ester complex, and continue stirring for 10–15 minutes to obtain a light yellow transparent passivation solution; the viscosity of the passivation solution at 25°C should not exceed 3.5 mPa·s, and the Karl Fischer moisture content should be controlled at 120–220 ppm.

[0042] Turn the powder bed at 12–20 rpm for 5–8 minutes to allow the solder powder to fall in a continuous, loose, silvery-gray waterfall pattern. Then, activate the two-fluid nitrogen atomizing nozzle, with a nozzle-to-powder bed distance of 60–90 mm, atomizing nitrogen pressure of 0.10–0.13 MPa (gauge pressure), passivation solution feed rate of 0.70–0.78 parts by mass / min, and spraying time of 75–85 minutes. Maintain the powder bed temperature at 21–23°C during spraying. Under normal conditions, the powder will not form wet clumps or mirror-like wet spots, but will gradually change from a slightly dry metallic gray to a soft silvery-gray. If localized shiny wet spots appear, stop spraying and continue turning the powder until the wet spots disappear.

[0043] After spraying, continue dry mixing at 12–20 rpm for 20–30 minutes. Then, raise the jacket temperature to 32–38°C and perform stepped vacuum drying: purging with nitrogen at atmospheric pressure for 6–10 minutes, maintaining 55–65 kPa (absolute pressure) for 6–10 minutes, maintaining 20–30 kPa (absolute pressure) for 8–12 minutes, and maintaining 5–8 kPa (absolute pressure) for 60–75 minutes, with constant low-speed turning at 8–12 rpm throughout the process. The vacuum system uses an explosion-proof diaphragm pump or a dry screw pump. The condenser temperature does not exceed -10°C, and the condensate is continuously collected. The powder mixer, nozzles, powder conveying pipes, and receiving tank are all grounded, with a grounding resistance not exceeding 10Ω. The lower explosive limit of the drying exhaust gas outlet is normally below 10%. After drying, do not use air to backpressure. Instead, use dry nitrogen to slowly backpressure to atmospheric pressure over a period of not less than 1.5–3.0 minutes to obtain 880–890 parts by weight of SAC305 Type 5 solder powder with surface passivation treatment. The residual solvent should be less than 300 ppm.

[0044] When testing the passivated solder powder, take 1.8–2.2 g of solder powder and add 18–22 mL of a 1:1 mixture of anhydrous isopropanol and toluene. Mix by roller mixing at 23–27°C for 8–12 minutes, centrifuge at 2800–3200 rpm for 4–6 minutes, repeat the washing process three times, and then dry at 30–40°C and 6–10 kPa for 25–35 minutes. After the above washing process, the solder powder surface should still exhibit X-ray photoelectron spectroscopy (XPS) signals of Si and P. In this embodiment, the Si content on the XPS surface is 0.86 ± 0.13 at%, and the P content is 0.24 ± 0.05 at%. 1.3 Preparation of Dual-Latent Halogen-Free Flux

[0045] Based on a total of 100 parts by mass of dual-latency halogen-free flux, each component should be selected within the following range, and the total amount of dual-latency halogen-free flux should be normalized to 100 parts by mass by adjusting the amount of solvent subsystem or resin / film-forming subsystem; in actual preparation, the total amount of flux can be scaled up or down proportionally according to 110–120 parts by mass of flux.

[0046] The resin / film-forming subsystem includes: hydrogenated rosin glycerol ester, with an acid value of 8–12 mgKOH / g, comprising 26.0–30.0 parts by weight; polymerized rosin, with a softening point of 110–125℃, comprising 10.5–13.5 parts by weight; terpene phenolic resin, with a hydroxyl value of 45–65 mgKOH / g, comprising 4.5–6.5 parts by weight; and low acid value acrylic resin, with a glass transition temperature of 48–56℃, comprising 3.3–4.8 parts by weight.

[0047] The solvogenetic system comprises: 5.8–7.2 parts by mass of tetrahydrofurfuryl alcohol, 6.5–8.0 parts by mass of dipropylene glycol monomethyl ether, 10.0–12.2 parts by mass of diethylene glycol monobutyl ether, and 7.0–8.5 parts by mass of propylene glycol phenyl ether.

[0048] The low-temperature latent activator comprises: 1.6–2.2 parts by weight of succinic acid / N,N-diisopropylethanolamine salt and 1.3–2.0 parts by weight of glutaric acid / 2-methylimidazolium salt.

[0049] The high-temperature latent activator II comprises: 2.8–3.8 parts by weight of dodecenyl succinic anhydride-rosin alcohol half ester and 2.1–3.0 parts by weight of sebacic acid mono-2-hydroxyethyl ester / tributylamine salt.

[0050] The thixotropic system includes: hydrogenated castor oil micron powder with a D90 particle size of 5–10 μm in 3.5–4.8 parts by weight, and polyamide wax micron powder with a D90 particle size of 5–10 μm in 1.8–2.8 parts by weight.

[0051] The corrosion inhibitor / antioxidant subsystem includes: 0.20–0.45 parts by weight of benzotriazole, 0.15–0.35 parts by weight of methylbenzotriazole, 0.45–0.80 parts by weight of hindered phenolic antioxidant, and 0.15–0.40 parts by weight of triphenyl phosphite.

[0052] The non-fluorinated wetting / defoaming system includes: 0.25–0.55 parts by weight of polyether-modified polysiloxane, 0.15–0.35 parts by weight of acetylenic diol nonionic wetting agent, and 0.08–0.25 parts by weight of low-foaming polyether leveling agent.

[0053] The post-weld acid fixative includes 0.35–0.65 parts by weight of hindered tertiary amine proton scavenger.

[0054] Vacuum defoaming aids include: 0.15–0.40 parts by weight of non-silicone polyether defoamer.

[0055] The low-temperature latent activator should meet the following specifications: the acid / amine molar ratio of succinic acid / N,N-diisopropylethanolamine salt is 1.00:0.95–1.00:1.10; the acid / base molar ratio of glutaric acid / 2-methylimidazolium salt is 1.00:0.85–1.00:1.05; the water content is not higher than 0.15% by mass; the D90 is not greater than 12μm; the differential scanning calorimetry main thermal transition peak is 130–150℃; and the initial free acid proportion, calculated as total acid, is not higher than 18%.

[0056] The high-temperature latent activator should meet the following specifications: the acid value of dodecenyl succinic anhydride-rosin alcohol half ester is 70–115 mg KOH / g, and the residual anhydride group is not higher than 6.0% by mass; the acid / amine molar ratio of sebacic acid mono-2-hydroxyethyl ester / tributylamine salt is 1.00:0.95–1.00:1.10; the differential scanning calorimetry main thermal transition or dissociation peak is 185–205℃, the moisture content at 25℃ is not higher than 0.12% by mass, and the insoluble matter after filtration is not higher than 0.05% by mass.

[0057] In this embodiment, the ratio of effective carboxyl equivalent to solder powder specific surface area is controlled to be approximately 1.02 mmol / m².

[0058] The aforementioned functional raw materials should further meet the following physicochemical requirements for repeated procurement and replacement: The low-acid-value acrylic resin is preferably a copolymer of at least two monomers selected from methyl methacrylate, butyl acrylate, and hydroxyethyl methacrylate, with an acid value not exceeding 8 mg KOH / g, a hydroxyl value of 20–60 mg KOH / g, a number-average molecular weight of 8000–25000, a polydispersity index of 1.8–3.5, and a glass transition temperature of 48–56℃; the hindered phenolic antioxidant is a 3,5-di-tert-butyl-4-hydroxyphenyl propionate or bisphenol antioxidant, preferably pentaerythritol tetra[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] or octadecyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate; the hindered tertiary amine proton scavenger is... The defoamer comprises β-hydroxyalkyl tertiary amines or hindered piperidine derivatives containing tertiary amine nitrogen and having a boiling point not lower than 180℃, with a tertiary amine equivalent of 120–280 g / eq and a conjugate acid acidity coefficient of 8.5–10.5; the non-silicone polyether defoamer is ethylene oxide / propylene oxide block or random polyether with a number average molecular weight of 1000–5000, a hydrophilic-lipophilic balance value of 2–8, a water content not exceeding 0.10% by mass, and no siloxane structure; the polyether-modified polysiloxane has a viscosity of 50–600 mPa·s at 25℃ and an active ingredient content not less than 95% by mass; the preferred acetylenic diol nonionic wetting agent is acetylenic diol ethoxylate with a hydrophilic-lipophilic balance value of 6–12; the low-foaming polyether leveling agent is ethylene oxide / propylene oxide polyether with a hydrophilic-lipophilic balance value of 4–10.

[0059] In a 400–600 mL sealed jacketed reactor equipped with an anchor stirrer, rotor-stator shear head, nitrogen protection, condenser reflux device, oxygen content monitoring, and pressure relief structure, first add tetrahydrofurfuryl alcohol, dipropylene glycol monomethyl ether, diethylene glycol monobutyl ether, and propylene glycol phenyl ether. Start the anchor stirrer at 100–150 rpm, maintain a slight positive nitrogen pressure of 3–5 kPa (gauge pressure) inside the reactor, and use nitrogen flow rate only to maintain the slight positive pressure, recommended at 20–60 mL / min·L reactor volume. The oxygen content at the reactor top should not exceed 1.5% by volume. The condenser outlet temperature should be controlled at 8–12°C, and the reactor pressure should be controlled between atmospheric pressure and +5 kPa (gauge pressure). Do not pressurize in a sealed manner. The temperature is increased from 20–25℃ to 130–138℃ at a rate of 1.0–1.5℃ / min. During the heating process, the temperature at the top of the vessel should not exceed 85℃. If the temperature at the top of the vessel continues to exceed 95℃, the jacket temperature should be reduced or the condensation efficiency should be increased to avoid excessive loss of light components.

[0060] When the system reaches 65–75°C, hydrogenated rosin glycerol ester is added; when it reaches 88–96°C, polymerized rosin is added; and when it reaches 112–122°C, terpene phenolic resin and low-acid-value acrylic resin are added. Initially, the solution in the reactor is a honey-like turbid suspension. As the temperature rises to 124–132°C, the edges of the resin particles gradually disappear, and the liquid surface changes from a turbid amber color to a transparent amber color. After reaching 130–138°C, the temperature is maintained for 25–35 minutes until no visible gel particles are visible when the sample passes through an 80–120 μm filter.

[0061] Set the jacket to 84–88°C and cool at a rate of 0.6–1.0°C / min. Once the reactor temperature has dropped to 84–88°C, add dodecenyl succinic anhydride-rosin alcohol half ester over 5–8 minutes, followed by sebacic acid mono-2-hydroxyethyl ester / tributylamine salt over 4–7 minutes. A slight bluish-white microemulsion will appear during the addition process, but no milky turbidity or oil droplets should be observed. Continue to maintain the temperature at 84–88°C for 15–22 minutes to allow the high-temperature latent activator to disperse in the continuous resin phase.

[0062] Continue cooling to 70–74°C. Pre-finely grind succinic acid / N,N-diisopropylethanolamine salt and glutaric acid / 2-methylimidazolium salt to a D90 ≤ 12 μm, and uniformly add them over 6–10 minutes using a drying funnel. After addition, the system changes from a transparent amber color to a translucent gel precursor with a slight bluish sheen. The stirring torque is slowly increased from approximately 0.15–0.22 N·m to approximately 0.28–0.36 N·m. This torque increase is used to determine the formation of reversible ionic association sites in the resin solvation microregions by the acid amine salts at low temperatures.

[0063] After cooling to 60–65°C, add benzotriazole, methylbenzotriazole, hindered phenolic antioxidant, triphenyl phosphite, polyether-modified polysiloxane, acetylenol nonionic wetting agent, low-foaming polyether leveling agent, hindered tertiary amine proton scavenger, and non-silicone polyether defoamer. Continue anchoring stirring for 12–18 minutes until the system returns to a uniform, translucent amber color.

[0064] Cool the system to 52–56°C and switch to rotor-stator shearing at 2500–3100 rpm. Slowly add hydrogenated castor oil powder and polyamide wax powder through a 50–80 mesh sieve over a total feeding time of 8–12 minutes. Initially, fine white vortices appear in the system after powder addition; these vortices gradually disappear after about 10–15 minutes, and the liquid surface becomes thick but still self-leveling. Continue shearing at 52–56°C for 60–80 minutes, increasing the torque from approximately 0.28–0.36 N·m to approximately 0.55–0.80 N·m and reaching a plateau.

[0065] The hot flux was cooled to 30–36°C and milled twice using a three-roll mill. The first mill had a roller gap of 20–30 μm / 8–12 μm, and the second mill had a roller gap of 8–12 μm / 4–6 μm. The discharge temperature was controlled at 30–35°C. The maximum particle size detected by the scraper fineness gauge was less than 8.0 μm. Subsequently, the flux was degassed at low speed for 12–20 minutes at 22–26°C and 8–12 kPa absolute pressure to obtain 110–120 parts by weight of dual latent halogen-free flux. 1.4 Three-stage vacuum mixing and curing of solder paste

[0066] 880–890 parts by weight of surface-passivated SAC305 Type 5 solder powder and 110–120 parts by weight of double-latent halogen-free flux were equilibrated at 20–25°C for 2–4 hours under sealed conditions. The oxygen content in the mixing chamber was controlled below 300 ppm, and the dew point was below -45°C. The mixing cup, scraper, and impeller were purged with dry nitrogen for 8–12 minutes and then wiped with anhydrous isopropanol and completely dried.

[0067] The mixing process utilizes a dual planetary blade vacuum mixer with a mixing cup inner diameter of 90–100 mm, an effective loading volume of 235 ± 10 ml, an equivalent radius of 30–38 mm for each blade, and an average clearance of 1.0 ± 0.2 mm between the blade outer edge and the cup wall. The equivalent wall shear rate is estimated using γeq = 2πRN / δ, where R is the equivalent blade radius, δ is the blade-wall clearance, and N is the blade rotation speed in s⁻¹ (revolutions per minute at 60 rpm). This formula is used to determine the minimum scalable equivalent shear window. During production scale-up, the equivalent shear rate, temperature rise, torque plateau, and the presence of a continuous bright metallic film on the cup wall are used as common control indicators.

[0068] The first stage is low-shear pre-wetting. Place all flux at the bottom of the mixing cup and spread it into a continuous paste layer approximately 6–10 mm thick. Start low-shear stirring, controlling the impeller speed at 3.5–5.0 rpm, corresponding to an equivalent shear rate of approximately 12–18 s⁻¹. Add passivated solder powder via a screw-type powder feeder at a rate of 35–45 parts by mass / min over a period of 20–24 minutes. For the first 5 minutes, the system will be in a wet, sandy state, with a small amount of silvery-gray particles adhering to the cup walls; around 12 minutes, the wet sand will gradually shrink into a viscous paste; at the end of the powder addition, the system should form a continuous, silvery-gray paste without any dry powder flying around. Continue low-shear pre-wetting for 5–8 minutes after the powder addition is complete; the torque curve during this stage is allowed to fluctuate in a sawtooth pattern, but there should be no peak exceeding 40% of the baseline.

[0069] The second stage is short-duration high-shear dispersion. The blade speed is increased to 35–40 rpm, corresponding to an equivalent shear rate of approximately 120–150 s⁻¹, lasting for 8–10 minutes, with a cumulative equivalent shear rate of approximately 6.0 × 10⁻¹. 4 –9.0×10 4 The jacket cooling water is set at 16–20℃, and the paste temperature is raised from 20–25℃ to no higher than 24–26℃. During this stage, the paste transforms from a coarse, wet, sandy mass into a uniform, silvery-gray paste with a metallic luster. When the blades tumble, short, blunt ridges are formed, and long filaments, continuous mirror-like films, or dark particles should not appear. During production scale-up, the second stage should simultaneously meet a cumulative equivalent shear rate of 4.0 × 10⁻⁶. 4 –1.3×10 5 The temperature rise of the paste should not exceed 4.0℃, the torque plateau fluctuation should not exceed 10%, and there should be no continuous metallic film on the cup wall. If a continuous metallic film appears on the cup wall, it should be judged as an over-shear deviation.

[0070] The third stage involves stepped vacuum degassing and low-shear shaping. The equivalent shear rate is reduced to 10–15 s⁻¹, and the vacuum is applied in the following steps: 25–35 kPa for 2–4 minutes, 15–20 kPa for 4–6 minutes, and 8–12 kPa for 6–10 minutes. During this stage, small, silvery-gray bubbles first appear on the surface of the paste, and then the bubbles slowly burst along a low-shear tumbling trajectory; the vacuum should not be reduced to below 5 kPa in one go to avoid inducing solvent boil-off and microbubble nucleation. After degassing, the pressure is slowly restored to atmospheric pressure over 1.5–3.0 minutes using dry nitrogen. Transfer the mixed solder paste to a light-proof, airtight container, and purge the headspace of the container with dry nitrogen 2–4 times. Then, place it in a constant temperature oven at 3–8°C for 24–36 hours to cure. The cured solder paste should be a uniform silvery-gray color, free of visible oil separation, dark particles, and air bubbles; when a small amount of paste is picked up with a spatula, it should form a short peak, the tip of which should slowly fall back within 10–15 seconds without flowing. Before use, allow the solder paste to equilibrate at 20–25°C for 2–3 hours in a sealed state. 1.5 Test results of the solder paste obtained in Example 1-A

[0071] The solder paste obtained in Example 1-A has a net alloy powder content of 88.382% by mass and a solder powder content of 88.400% by mass after surface passivation treatment. The solder paste prepared according to the method of Example 1-A exhibits the following typical test results; however, the segmented weight loss in thermogravimetric analysis uses the separated dual-latent halogen-free flux as the test sample and is normalized based on the mass of this flux, not the mass of the entire solder paste. If calculated based on the mass of the entire solder paste, the weight loss of Example 1-A in the 80–120℃, 120–180℃, and 180–230℃ ranges is approximately 1.18% by mass, 3.82% by mass, and 2.11% by mass, respectively.

[0072] Initial viscosity, 25℃, 10s⁻¹ 217.6±8.9 Pa·s Viscosity drift after 90 days of storage at 25°C 9.6±2.3% Viscosity drift after storage at 40℃ for 31 days 17.8±3.5% Transfer efficiency decreases after 24-hour exposure of the steel mesh. 7.9±1.6% Differential scanning calorimetry first thermal transformation peak 143.2±2.8℃ Differential scanning calorimetry second thermal transition peak 197.4±3.4℃ Thermogravimetric analysis of weight loss at 80–120℃ (normalized based on flux mass). 10.2 ± 0.9% by mass Thermogravimetric analysis of weight loss at 120–180℃ (normalized based on flux mass). 32.9 ± 1.8 percent by mass Thermogravimetric analysis of weight loss at 180–230℃ (normalized based on flux mass). 18.2 ± 1.5% by mass Organic solder mask copper surface wetting retention rate after 25℃ / 90d 82.7±4.2% Wetting retention rate of electroless nickel-plated gold after 25℃ / 90d 87.9±3.8% 01005 Graphical Grape-like Unmerged Defect Rate 4.8±1.3% Bottom terminal device cavity area ratio 5.7±1.0% Surface insulation resistance, 85℃ / 85% relative humidity / 168h log10Ω = 10.05 ± 0.26 Electrochemical migration Dendrites were found in 0 out of 6 test plates. Corrosion of bronze mirrors L-class Note: The segmented weight loss in the thermogravimetric analysis in the table above is based on the separated dual-latency halogen-free flux as the sample and normalized based on the flux mass; these values ​​do not represent the mass loss of the entire solder paste. Based on the entire solder paste of Example 1-A, the converted weight loss values ​​for the three segments are approximately 1.18 mass percentage, 3.82 mass percentage, and 2.11 mass percentage, respectively.

[0073] The above embodiment is one specific implementation of the present invention. For other lead-free solder powder particle size grades or alloy systems under the same technical concept, the activator equivalent and mixing shear amount can be equivalently adjusted according to the solder powder specific surface area and oxide film thickness, while maintaining the thermally degradable passivation layer on the solder powder surface, the dual latent halogen-free activation system, the segmented volatile flux continuous phase, and the three-stage low-damage mixing steps. I. Experimental Samples

[0074] This section retains only the experimental samples, control variables, test items, experimental data, and data analysis conclusions directly related to the verification of the efficacy of this patented technology. Examples 1-A are used to characterize the complete synergistic system; Comparative Examples 1 to 5 are used to verify the performance degradation when the industry baseline is not met, the surface passivation layer is missing, the double latent activation system is missing, the same components are mixed in a non-interfacial manner, and the cumulative shear amount exceeds the limit.

[0075] The example and comparative variable matrix are as follows.

[0076] Example 1-A is positioned as the optimal embodiment of the present invention; the control variable is none; the key change is pyrolytic silicon / phosphorus / carboxylate passivation solder powder + dual latent halogen-free activator + three-stage mixing + segmented volatile flux; the purpose of setting it up is to demonstrate the complete synergistic system. Comparative Example 1 is positioned as the industry baseline / closest to the prior art; the control variable is the use of the traditional no-clean SAC305 Type 5 solder paste route; the key change is no solder powder surface passivation layer; no dual latent release; conventional acid amine salt / resin / thixotropic agent; one-time high-shear vacuum mixing; the purpose of setting it up is to establish an industrial baseline.

[0077] Comparative Example 2 is positioned as lacking core synergistic feature A; the control variable is the removal of the pyrolytic passivation layer on the surface of the solder powder; the key change is the retention of the dual latent activator, segmented solvent and three-stage mixing, but the solder powder is not pre-passivated; the purpose of this setting is to prove that the surface isolation layer is indispensable.

[0078] Comparative Example 3 was positioned as lacking core synergistic feature B; the control variable was the removal of the dual-latency halogen-free activator; the key change was the retention of passivation solder powder and three-stage mixing, but the replacement of the low-temperature / high-temperature latent activator with a conventional free dicarboxylic acid / amine salt mixture with an equivalent carboxyl group; the purpose of this setting was to demonstrate that the heat release sequence is indispensable.

[0079] Comparative Example 4 is positioned as a conventional equivalent replacement / breaking of spatiotemporal linkage; the control variables are the same chemical substances but without pre-passivation of the solder powder surface; the key change is that organosilicon, phosphate ester, and resin acid salt are directly added to the flux and then mixed with the solder powder; the purpose of this setting is to prove that physical mixing of the same components does not equal interface structure.

[0080] The positioning of Comparative Example 5 is that the core parameter exceeds the limit; the control variables are the same as those in Example 1 in terms of substances and steps, except that the cumulative shear amount in the second stage exceeds the limit; the key change is that the second stage is changed from 135.0 s⁻¹ × 9.0 minutes to 385.0 s⁻¹ × 14.0 minutes; the purpose of setting this is to prove that the cumulative shear amount is the critical life and death line. II. Preparation of Examples and Comparative Examples

[0081] The preparation setup for Example 1-A was as follows: pyrolytic silicon / phosphorus / carboxylate passivating solder powder; dual latent halogen-free activator; three-stage mixing; and segmented volatile flux. Key phenomena observed during its preparation or aging process were: during passivation, the powder bed exhibited a continuous silver-gray powder cascade without wet spots or bright oil spots; after the addition of the high-temperature latent activator, the flux only showed a slight bluish-white micro-emulsification; after the second stage, the paste exhibited a uniform metallic luster, forming short, blunt ridges when pulled, and step-vacuum degassing without sudden boiling. Experimental results indicated: a stable torque plateau, controlled temperature rise, silicon / phosphorus signals remaining in the X-ray photoelectron spectroscopy after elution, and complete differential scanning calorimetry dual release peaks and thermogravimetric analysis three-stage weight loss curves.

[0082] The preparation settings for Comparative Example 1 were: traditional no-clean SAC305 Type 5 solder paste; no passivation layer, no double latent release; high-shear vacuum mixing after one-time powder addition. Key phenomena during its preparation or aging process were: fine mist-like filaments appeared on the flux surface when cooled to below 60℃; a silver-gray dry powder ring formed around the impeller in the early stage of mixing, and a dark gray paste film appeared on the cup wall; after accelerated aging at 40℃, the paste darkened, and a grainy feel was noticeable when lifted with a spatula. The experiment indicated that the traditional acid-amine salt / resin / thixotropic agent system can form an initial solder paste, but the activator is consumed by the solder powder oxide film during storage, resulting in significant thickening later.

[0083] The preparation setup for Comparative Example 2 was as follows: the thermally degradable passivation layer on the solder powder surface was removed, while the dual latent activator, segmented solvent, and three-stage mixing from Example 1 were retained. Key phenomena observed during its preparation or aging process were: a steeper torque increase after the unpassivated solder powder came into contact with the flux in the first stage; a thin, grayish-white, waxy ring appeared on the cup wall approximately 9 minutes after powder addition; a slight gritty feel was observed when scraping a thin layer after aging; and the viscosity rapidly increased after aging at 40°C for 7–10 days. The experiments indicate that the dual latent activator cannot replace interfacial isolation during storage, and exposed SnO / SnO2 will still consume the activator and generate metal salts.

[0084] The preparation setup for Comparative Example 3 was as follows: passivation solder powder and three-stage mixing were retained, but the dual-latentation system of low-temperature / high-temperature latent activators was eliminated, and conventional free dicarboxylic acids / amine salts were used as substitutes. Key phenomena observed during the preparation or aging process were: a brief period of milky white turbidity appeared after the addition of conventional free dicarboxylic acid, and thin acid crystal streaks were observed on the reactor wall; the activity was released prematurely during the reflow preheating stage, and some solder powder was not timely combined and formed grape-like uncombined rudiments in the early melting stage. The experiment indicates that the presence of the passivation layer alone cannot guarantee film removal before melting; the lack of a dual-release sequence will cause the reflow wetting window to collapse.

[0085] The preparation setup for Comparative Example 4 was as follows: the same chemical substances as in Example 1 were used, but the solder powder was not pre-passivated; organosilicon, phosphate ester, and resin acid salt were directly added to the flux and then mixed. Key phenomena observed during its preparation or aging process were: 0.2–0.5 mm transparent fish-eye-like particles appeared in the flux, with tailing after three-roll milling; a grayish-white fish-scale-like film appeared on the cup wall during mixing, revealing dark and light stripes after scraping; and the silicon / phosphorus signal in the X-ray photoelectron spectroscopy of the solder powder was extremely weak after elution. The experiment indicates that physical mixing of the same components cannot form a continuous, pyrolytic interface layer, proving that this method relies on spatial interface positioning rather than a simple list of components.

[0086] The preparation settings for Comparative Example 5 were the same as in Example 1, except that the cumulative high-shear amount in the second stage was increased from 7.29 × 10⁻⁶. 4 Increased to 3.234×10 5The key phenomena observed during its preparation or aging process are as follows: after 90 seconds of high shear, the paste exhibits a highly reflective, polished slurry state; at 4 minutes, a continuous metallic bright film forms on the cup wall, and the temperature rises to approximately 31.6℃; after 14 minutes, the torque increases a second time, and after degassing, the bubbles rupture, leaving behind small, dark gray pores. The experiment indicates that exceeding the cumulative shear limit will mechanically erode the passivation layer, leading to a decrease in the silicon / phosphorus surface signal and causing simultaneous deterioration in storage, wetting, and voiding properties. III. Testing

[0087] The testing items focused on the process, interface structure, heat release behavior, rheological stability, welding defects, and electrical reliability. Each test method was performed under fixed sample treatment conditions to ensure comparability between the examples and comparative examples.

[0088] Before particle size testing, solder powder samples should be taken under an inert atmosphere or low humidity conditions to avoid deviations in D10, D50, and D90 due to moisture absorption or agglomeration; before specific surface area testing, low-temperature degassing conditions that do not damage the pyrolytic passivation layer should be used.

[0089] The indicators for powder particle size testing are D10, D50, and D90 particle sizes. An example of the instrument type or model is a laser particle size analyzer, such as the Malvern Laser Particle Size Analyzer 3000. The standard or basis is ISO 13320:2020.

[0090] The index for testing the specific surface area of ​​powder is specific surface area m² / g. An example of the instrument type or model is specific surface area analyzer, and the standard or basis is ISO9277:2022.

[0091] The oxygen content test index for powder is Oppm. The instrument type or model example is an oxygen, nitrogen and hydrogen elemental analyzer, inert gas melting method, and the standard or basis is to use inert gas melting-thermal conductivity / infrared detection method. The principle of the method can refer to ASTM E1019, and a calibration curve is established using tin-based solder powder standard sample or spiked sample.

[0092] The indicators for surface passivation layer testing are silicon / phosphorus ratio, SnO / SnO2 ratio, and depth of ablation using X-ray photoelectron spectroscopy. The instrument type or model is X-ray photoelectron spectroscopy, such as Thermo Fisher Surface Analyzer. The standard or basis is ISO 15472 for X-ray photoelectron spectroscopy binding energy scale calibration. The silicon / phosphorus surface element content and SnO / SnO2 peak area ratio are determined according to the fixed elution pretreatment and instrument quantitative procedure.

[0093] The indicator for thermal release spectrum testing is the differential scanning calorimetry double release peak. The instrument type or model is, for example, differential scanning calorimetry, such as differential scanning calorimeter. The standard or basis is ASTM E1356.

[0094] The parameters for the fractional volatilization test are weight loss at 80–120℃, 120–180℃, and 180–230℃ using thermogravimetric analysis. The instrument type or model is thermogravimetric analysis, such as a thermogravimetric analyzer. The standard or basis is ASTM E1131. The thermogravimetric analysis sample is either the separated flux or the organic phase obtained by solvent extraction. The results are normalized based on the flux / organic phase mass.

[0095] The rheological test parameters are viscosity, yield stress, and three-stage thixotropic recovery. Examples of instrument types or models include: Anton Paar Rotational Rheometer 302; and Macon Solder Paste Viscometer 205. The standard or basis is a rotational rheometer at 25℃ for 10s⁻¹. If using the IPC-TM-650 system, select IPC-TM-650 2.4.34 or 2.4.34.1 according to the sample viscosity range, and specify the rotor, shear rate, equilibrium time, and temperature; and the internal three-stage thixotropic recovery method.

[0096] The slump test index is cold / hot slump, and the instrument category or model example is IPC standard steel mesh / hot blast furnace, and the standard or basis is IPC-TM-6502.4.35.

[0097] The indicators for solder ball / merging test are solder ball grade and unmerged bobble. An example of the instrument type or model is hot stage / reflow oven + optical microscope. The standard or basis is IPC-TM-6502.4.43.

[0098] The wetting test index is the wetting area retention rate of the organic solder mask copper surface / chemical nickel-plated gold surface. The instrument type or model example is reflow oven + image analysis, and the standard or basis is IPC-TM-6502.4.45 or equivalent image analysis method.

[0099] The indicator for void testing is the void area ratio of bottom terminal components. The instrument type or model example is an X-ray detector. The standard or basis is an internal bottom terminal component test board, and the statistical method is image-based.

[0100] The indicators for electrical reliability testing are surface insulation resistance and electrochemical migration. An example of the instrument type or model is a constant temperature and humidity bias chamber + high resistance meter. The standard or basis is IPC-TM-6502.6.3.7 or equivalent surface insulation resistance / electrochemical migration conditions.

[0101] The corrosion test index is copper mirror corrosion. Examples of instrument categories or models are copper mirror, constant temperature chamber, and optical observation. The standard or basis is IPC-TM-6502.3.32. The indicators for halogen-free / halogenated testing are Cl⁻, Br⁻, F⁻, I⁻, total ionic halides, and total halogens. Examples of instrument types or models are ion chromatographs and combustion ion chromatographs. The standard or basis is that ionic halides are determined by ion chromatography of flux water extracts. Total halogens can be determined by combustion ion chromatography methods according to EN14582 or IEC62321-3-2. Evaluation is based on the J-STD-004 series low-halogen 0-level / halogen-free limits. IV. Performance Testing

[0102] Each group of samples was compared under the same aging and reflux conditions. Unless otherwise specified, 1000g of each sample was prepared, and the test results are expressed as mean ± standard deviation for n=3; the aging conditions were 25℃ / 90d and 40℃ / 31d.

[0103] To ensure the reproducibility of the results for wetting, uncoated grape-like structures, voids, and surface insulation resistance / electrochemical migration in Tables 1 and 2, the test conditions were fixed as follows: Aging samples were placed in sealed polypropylene containers and stored at 25±1℃ for 90 days and 40±1℃ for 31 days, respectively. Printing was performed using a 100μm thick electropolished stainless steel mesh, with a squeegee speed of 50mm / s, a squeegee pressure of 0.20–0.30MPa, and an ambient temperature of 23±2℃ and relative humidity of 40–60%. Reflow was performed using a hot air reflux curve, with a heating rate of 1.0–1.5℃ / s, a holding time of 90±10s at 150–200℃, a liquid phase time of 55±5s above 217℃, a peak temperature of 245±3℃, and a cooling rate of 2.0–3.0℃ / s.

[0104] Wetting tests on the organic solder resist copper surface and the electroless nickel-plated gold surface were conducted using standard test boards from the same batch. The organic solder resist copper surface test board underwent thermal aging at 150℃ for 4 hours before testing, while the electroless nickel-plated gold surface test board was equilibrated at 23±2℃ and 40–60% relative humidity for 24 hours. The wetting area was statistically analyzed using image analysis software after photographing with an optical microscope, with no fewer than 30 pads per group. The wetting area retention rate was calculated as the ratio of the wetting area after aging to the wetting area of ​​the fresh sample × 100%. The 01005 pattern grape-like uncombined defect test used an open 01005 pattern stencil, with no fewer than 500 solder paste deposition points per group. After reflow, the presence of 3 or more uncombined solder particles in a single deposition point was considered a grape-like uncombined defect.

[0105] For bottom terminal components, void testing uses 6mm×6mm square flat leadless test devices with a central hot-swappable pad area of ​​4.0mm×4.0mm. The stencil opening adopts a windowed design, with an effective printing coverage of 50–60%. Each group has no fewer than 20 pads. After X-ray imaging, the void area is statistically analyzed using a uniform grayscale threshold. The void area ratio = total void area / effective soldering area of ​​pads × 100%. Surface insulation resistance / electrochemical migration testing uses comb-shaped electrode test boards with an electrode spacing of 0.5mm. After reflow, no cleaning is performed. A 50V DC bias is applied for 168 hours at 85℃ / 85% relative humidity. Surface insulation resistance is expressed as log10Ω. Electrochemical migration is determined by the number of visible dendrites or migration channels in 6 test boards.

[0106] Data verification instructions: The test data in Tables 1, 2 and 3 are archived according to the single-point formulation, fixed aging conditions, fixed reflux curve and the same test standard of Example 1-A; among them, the segmented weight loss of thermogravimetric analysis is normalized based on the mass of the separated flux or organic phase, the surface insulation resistance is expressed as log10Ω, and the halogen-free and halide detection is based on the flux mass.

[0107] Second stage maximum ointment temperature / ℃ 24.1±0.5 29.4±1.1 24.7±0.6 24.5±0.5 24.9±0.7 31.6±1.0 Second stage torque plateau fluctuation / % 6.4±0.9 20.8±2.7 16.9±1.9 10.8±1.5 18.3±2.2 24.7±3.0 After the ointment defoams, the number of microbubbles visible is [number] per cm². 1.3±0.5 5.7±1.4 4.1±0.8 3.0±0.7 4.6±1.1 6.2±1.6 X-ray photoelectron spectroscopy (XPS) of Si / at% after solder powder removal 0.86±0.13 <0.03 <0.03 0.82±0.12 0.15±0.06 0.36±0.09 X-ray photoelectron spectroscopy (P / at%) after solder powder removal 0.24±0.05 <0.01 <0.01 0.22±0.04 0.035±0.018 0.08±0.03 Equivalent thickness of passivation layer / nm 3.35±0.48 0 0 3.28±0.43 0.62±0.21 1.18±0.31 Differential scanning calorimetry first release peak / ℃ 143.2±2.8 126.7±6.1, broad peak 142.6±2.9 119.5±4.6, broad peak 134.1±7.2, trailing 142.8±3.1 Differential scanning calorimetry second release peak / ℃ 197.4±3.4 No clear peak observed 197.1±3.5 No clear peak observed 183.9±8.4, weak peak 197.0±3.5 Thermogravimetric analysis of weight loss at 80–120℃ (normalized based on flux mass). 10.2±0.9 16.7±1.3 10.5±1.0 13.6±1.1 12.4±1.2 9.1±1.0 Thermogravimetric analysis of weight loss at 120–180℃ (normalized based on flux mass). 32.9±1.8 22.1±1.9 33.5±1.7 25.9±1.8 28.1±2.0 30.2±2.1 Thermogravimetric analysis of weight loss at 180–230℃ (normalized based on flux mass). 18.2±1.5 29.6±2.0 18.7±1.6 25.3±1.8 26.6±1.9 22.9±1.8 Infrared index of Sn-carboxylate, 40℃ / 31d 0.29±0.06 1.00±0.13 0.79±0.10 0.48±0.08 0.72±0.11 0.64±0.09 Preparation time before mixing (excluding low-temperature curing) / h Approximately 5.9 Approximately 3.2 Approximately 5.0 Approximately 5.7 Approximately 5.5 Approximately 5.9 Volatile organic compound condensation recovery load, relative value 1.18±0.07 1.00±0.05 1.17±0.06 1.16±0.06 1.18±0.07 1.24±0.08 Note: The preparation time before mixing in Table 1 does not include the 24–36 h low-temperature curing at 3–8℃. The low-temperature curing conditions for Example 1-A were 5.0℃ for 30.0 h, so the complete preparation cycle including curing was approximately 35.9 h.

[0108] Table 2. Data on terminal materials and welding performance Initial viscosity, 25℃, 10 s⁻¹ / Pa·s 217.6±8.9 198.4±9.6 213.8±10.1 211.5±8.5 222.9±11.4 229.7±12.8 Viscosity drift at 25℃ / 90d / % 9.6±2.3 39.8±6.2 33.7±5.4 24.6±4.5 31.9±5.7 36.4±6.1 Viscosity drift at 40℃ / 31d / % 17.8±3.5 69.4±8.7 56.8±7.3 41.6±6.0 55.1±7.9 49.7±7.0 Transfer efficiency decreases after 24-hour exposure of the steel mesh / % 7.9±1.6 22.8±3.9 17.9±3.1 14.7±2.8 19.4±3.5 18.2±3.3 Thermal collapse, 180℃ / 1 minute Qualified, with clear edges Critical, Local Bridging critical qualified critical critical Solder ball test Preferred to acceptable Unqualified, clustered tin beads Critical, clustered tin beads Unacceptable, scattered solder beads Critical, clustered tin beads Critical, clustered tin beads Fresh sample organic solder mask copper surface wetting area / % 86.9±3.1 80.6±3.8 84.0±3.4 88.7±3.5 82.1±3.7 83.5±4.0 Retention rate of wetted area on copper surface of organic solder mask after 25℃ / 90d / % 82.7±4.2 52.4±6.8 63.8±5.9 60.5±6.2 61.7±6.0 58.9±6.4 Retention rate of wetted surface area after electroless nickel-gold plating at 25℃ for 90 days / % 87.9±3.8 64.1±6.6 73.2±5.4 70.6±5.8 71.8±5.7 68.5±6.1 Bottom terminal device void area ratio / % 5.7±1.0 13.2±1.9 9.4±1.5 11.1±1.6 12.0±1.8 10.3±1.6 Surface insulation resistance, log10Ω 10.05±0.26 8.77±0.33 9.13±0.29 8.91±0.34 9.02±0.32 9.18±0.31 Electrochemical migration 0 / 6 dendrites 2 / 6 dendrites 1 / 6 Suspected dendrites 2 / 6 dendrites 1 / 6 Suspected dendrites 1 / 6 Suspected dendrites Corrosion of bronze mirrors L-class M-level localized thinning L / M boundary M-level slight atomization L / M boundary L / M boundary Judgment Explanation: In the thermal collapse results, "pass" indicates that the solder paste pattern did not collapse beyond the limit or bridge after heating; "critical" indicates slight edge expansion, a small bridging trend, or a morphology close to the judgment threshold; "local bridging" indicates local connectivity between adjacent patterns. In the solder ball test, the acceptable critical level is selected. Clustered solder balls are unacceptable. The grade of scattered solder balls is determined according to the IPC-TM-6502.4.43 graphic grade and the statistical rules of the same image; clustered solder balls indicate that small solder balls are distributed in clusters around the main solder joint or in a local area, and scattered solder balls indicate that small solder balls are discretely distributed.

[0109] Table 3. Detection results of halogen-free and halide compounds in Example 1-A Cl⁻ 18.4±3.2ppm Ion chromatography; below the J-STD-004 series low-halogen 0-grade / halogen-free limit. Br⁻ <5.0ppm Ion chromatography; not detected or below the limit of quantitation F⁻ <5.0ppm Ion chromatography; not detected or below the limit of quantitation I⁻ <5.0ppm Ion chromatography; not detected or below the limit of quantitation Total ionic halides (Cl⁻+Br⁻+F⁻+I⁻) 24.7±4.1ppm The value is below the 500 ppm limit, meeting the requirements for low-halogen 0-level / halogen-free evaluation. Total halogens 118±15ppm Combustion ion chromatography; used to confirm the absence of a significant organic halogen source. Flux Classification Rosin-type low-activity grade 0 A comprehensive judgment is made based on the resin type, halide results, copper mirror corrosion, and surface insulation resistance / electrochemical migration results. V. Data Analysis Conclusions

[0110] Table 4 Key Improvements in Example 1-A Viscosity drift at 25℃ / 90d 39.8% 9.6% A decrease of approximately 75.9% Viscosity drift at 40℃ / 31d 69.4% 17.8% A decrease of approximately 74.4% Retention rate of wetted area on copper surface of organic solder mask after aging 52.4% 82.7% An increase of approximately 57.8%. Retention rate of wettable area on electroless nickel-plated gold surface after aging 64.1% 87.9% An increase of approximately 37.1%. Bottom terminal device cavity area ratio 13.2% 5.7% A decrease of approximately 56.8% Surface insulation resistance, log10Ω 8.77 10.05 An increase of approximately 1.28 orders of magnitude As shown in Tables 1 to 4, Example 1-A demonstrates advantages not only in a single indicator, but also in storage stability, stencil exposure stability, post-aging wetting, large pad void ratio, and electrical reliability. Compared to Comparative Example 1, Example 1-A exhibits significantly reduced viscosity drift at 25°C / 90d and 40°C / 31d, indicating that storage side reactions between the solder powder surface oxide film and the flux activator are effectively suppressed. Simultaneously, Example 1-A shows a slight increase in initial viscosity, pre-mixing preparation time (excluding curing), and volatile organic compound condensation recovery load compared to the industry baseline, reflecting its comprehensive improvement in storage, wetting, and reliability achieved through more complex interface engineering and inert protection processes. 5.1 Uncontrolled reaction during storage without passivation layer

[0111] Comparative Example 2, with the dual latent activators and three-stage mixing retained, only removed the pyrolytic passivation layer on the solder powder surface; the viscosity drift at 40℃ / 31d still reached 56.8%. This result indicates that if the SnO / SnO2 on the solder powder surface is not isolated, even if the activator has latent release characteristics, it will still be gradually consumed during storage and form metal salts or polar admixtures, leading to post-thickening of the solder paste. 5.2 During the release of the unparalleled stealth, the reflux wetting window collapses.

[0112] Comparative Example 3 retained the passivation solder powder but eliminated the low-temperature / high-temperature latent activator dual latent release system. This group showed improved storage stability compared to the industry baseline, but the rate of uncombined grape-like defects remained at 15.6%, and the wettability retention rate of the electroless nickel-plated gold surface after aging was only 70.6%. This indicates that the passivation layer must match the activator release window before reflow; otherwise, although the passivation layer can inhibit the reaction during storage, it will become an obstacle to film removal and wetting before melting. 5.3 Physical mixing of the same components cannot form interfacial synergy.

[0113] Comparative Example 4 used the same organosilicon, phosphate ester, resin acid salt, and dual latent activator as Example 1-A, but without pre-constructing these components onto the solder powder surface. The results showed that after elution, the silicon / phosphorus signals on the solder powder surface were only 0.15 at% and 0.035 at%, respectively; the viscosity drift at 40°C / 31 days was 55.1%; and the void area ratio for bottom terminal devices was 12.0%. These results demonstrate that the technical effectiveness of this patented solution relies on interfacial spatial positioning, rather than the ordinary physical mixing of similar substances. 5.4 Exceeding the limit for cumulative shearing will damage the passivation interface layer.

[0114] The material composition and procedures of Comparative Example 5 were the same as those of Example 1-A, except that the cumulative high-shear amount in the second stage was increased to 3.234 × 10⁻⁶. 5The results showed that the silicon / phosphorus signals in the X-ray photoelectron spectroscopy decreased to 0.36 at% and 0.08 at%, respectively, the equivalent thickness of the passivation layer decreased from approximately 3.35 nm to 1.18 nm, and the viscosity drift at 40 °C / 31 days increased to 49.7%. These results indicate that the cumulative shear rate in the second stage is not a typical process parameter, but rather a critical condition for protecting the pyrolytic passivation layer and maintaining the spatial distribution of the latent activation system. 5.5 Overall Conclusion

[0115] Example 1-A, through the synergistic effect of a thermally degradable passivation layer on the solder powder surface, a dual latent halogen-free activator, a segmented volatile flux continuous phase, and a three-stage low-damage mixing process, simultaneously reduces viscosity drift during storage, improves wettability retention after aging, reduces botryoidal uncoupling defects and large pad voids, and maintains a high surface insulation resistance, despite a slight increase in initial viscosity and preparation complexity. Five comparative examples demonstrate that the comprehensive performance of Example 1-A cannot be achieved without a surface passivation layer, without a dual latent activator, by changing the interfacial components to ordinary physical mixing, or by exceeding the shear accumulation limit.

[0116] Those skilled in the art will recognize that the units and algorithm steps of the various examples described in conjunction with the embodiments disclosed herein can be implemented in electronic hardware, or a combination of computer software and electronic hardware. Whether these functions are implemented in hardware or software depends on the specific application and design constraints of the technical solution. Those skilled in the art can use different methods to implement the described functions for each specific application, but such implementation should not be considered beyond the scope of this application.

[0117] Those skilled in the art will understand that, for the sake of convenience and brevity, the specific working processes of the systems, devices, and units described above can be referred to the corresponding processes in the foregoing method embodiments, and will not be repeated here.

[0118] In the several embodiments provided in this application, it should be understood that the disclosed systems, apparatuses, and methods can be implemented in other ways. For example, the apparatus embodiments described above are merely illustrative; for instance, the division of units is only a logical functional division, and in actual implementation, there may be other division methods. For example, multiple units or components may be combined or integrated into another system, or some features may be ignored or not executed. Furthermore, the coupling or direct coupling or communication connection shown or discussed may be through some interfaces; the indirect coupling or communication connection between apparatuses or units may be electrical, mechanical, or other forms.

[0119] The units described as separate components may or may not be physically separate. The components shown as units may or may not be physical units; that is, they may be located in one place or distributed across multiple network units. Some or all of the units can be selected to achieve the purpose of this embodiment according to actual needs.

[0120] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A method for preparing a surface passivation solder powder no-clean halogen-free solder paste, characterized in that: include, Based on 1000 parts by weight of the final solder paste, SAC305 Type 5 clean solder powder was sprayed under nitrogen to coat a thermally degradable composite passivation layer composed of 3-glycidyl etheroxypropyltrimethoxysilane pre-hydrolyzed oligomer, 2-ethylhexyl acid phosphate, and hydrogenated rosin acid / sebacic acid mono-2-hydroxyethyl ester complex. After vacuum drying, 880–890 parts by weight of surface passivated solder powder were obtained. This was then combined with a double-latent halogen-free flux containing succinic acid / N,N-diisopropylethanolamine salt, glutaric acid / 2-methylimidazolium salt, dodecenylsuccinic anhydride-rosin alcohol half ester, and sebacic acid mono-2-hydroxyethyl ester / tributylamine salt to make up to 1000 parts by weight. The solder paste was then subjected to low-shear pre-wetting, high-shear dispersion with a cumulative equivalent shear of 6.0 × 10^4–9.0 × 10^4, stepped vacuum degassing, and curing at 3–8°C for 24–36 hours to obtain the final solder paste.

2. The method for preparing a surface passivation solder powder no-clean halogen-free solder paste according to claim 1, characterized in that: The pyrolytic composite passivation layer comprises, based on 1000 parts by weight of the final solder paste, 0.05–0.08 parts by weight of 3-glycidyl etheroxypropyltrimethoxysilane prehydrolyzed oligomer, 0.02–0.04 parts by weight of 2-ethylhexyl acid phosphate, and 0.08–0.12 parts by weight of hydrogenated rosin acid / sebacic acid mono-2-hydroxyethyl ester composite; wherein the mass ratio of hydrogenated rosin acid to sebacic acid mono-2-hydroxyethyl ester composite is 1.5:1–2.5:1; and the solid content of the pyrolytic composite passivation layer is 0.012–0.050% by weight based on the mass of SAC305 Type 5 net solder powder.

3. The method for preparing a surface passivation solder powder no-clean halogen-free solder paste according to claim 2, characterized in that: The passivation solution used for spray coating is composed of 40–45 parts by weight of anhydrous isopropyl acetate, 16–20 parts by weight of n-heptane, 0.05–0.08 parts by weight of 3-glycidyl etheroxypropyltrimethoxysilane, 0.0055–0.0101 parts by weight of deionized water, 0.001–0.003 parts by weight of glacial acetic acid, 0.02–0.04 parts by weight of 2-ethylhexyl acid phosphate, and 0.08–0.12 parts by weight of hydrogenated rosin acid / sebaceous acid mono-2-hydroxyethyl ester complex, with a water / silicon molar ratio of 1.45–1.65, based on 1000 parts by weight of the final solder paste. The passivation solution is pre-hydrolyzed at 20–25°C for 15–25 minutes, then 2-ethylhexyl acid phosphate and hydrogenated rosin acid / sebacic acid mono-2-hydroxyethyl ester complex are added and stirring is continued for 10–15 minutes; the spraying rate is 0.70–0.78 parts by mass / min and the spraying time is 75–85 minutes; after spraying, dry mixing is carried out for 20–30 minutes, and then step vacuum drying is performed at 32–38°C.

4. The method for preparing a surface passivation solder powder no-clean halogen-free solder paste according to claim 1, characterized in that: The alloy composition of the SAC305 Type 5 solder powder, by mass percentage, is 2.8–3.2% silver, 0.4–0.6% copper, and the balance tin; the D10, D50, and D90 particle sizes of the SAC305 Type 5 solder powder are 10–14 μm, 17–23 μm, and 25–32 μm, respectively; the specific surface area is 0.045–0.060 m² / g; the total oxygen content of the powder is 400–650 ppm; the thickness of the primary oxide film is 2.5–3.8 nm; the SnO / SnO2 peak area ratio measured by X-ray photoelectron spectroscopy is 0.70–1.20; and the sphericity is not less than 0.

94.

5. The method for preparing a surface passivation solder powder no-clean halogen-free solder paste according to claim 1, characterized in that: The dual-latent halogen-free flux comprises, by weight, 26.0–30.0 parts of hydrogenated rosin glycerol ester with an acid value of 8–12 mgKOH / g; 10.5–13.5 parts of polymerized rosin with a softening point of 110–125℃; 4.5–6.5 parts of terpene phenolic resin with a hydroxyl value of 45–65 mgKOH / g; 3.3–4.8 parts of low-acid-value acrylic resin with a glass transition temperature of 48–56℃; and 5.8– 7.2 parts by weight; 6.5–8.0 parts by weight of dipropylene glycol monomethyl ether; 10.0–12.2 parts by weight of diethylene glycol monobutyl ether; 7.0–8.5 parts by weight of propylene glycol phenyl ether; 1.6–2.2 parts by weight of succinic acid / N,N-diisopropylethanolamine salt; 1.3–2.0 parts by weight of glutaric acid / 2-methylimidazolium salt; 2.8–3.8 parts by weight of dodecenylsuccinic anhydride-rosin alcohol half ester; 2.1–3.0 parts by weight of sebacic acid mono-2-hydroxyethyl ester / tributylamine salt.

6. The method for preparing a surface passivation solder powder no-clean halogen-free solder paste according to claim 5, characterized in that: The dual-latency halogen-free flux further includes: hydrogenated castor oil micro powder with a D90 particle size of 5–10 μm, in a concentration of 3.5–4.8 parts by weight; polyamide wax micro powder with a D90 particle size of 5–10 μm, in a concentration of 1.8–2.8 parts by weight; benzotriazole 0.20–0.45 parts by weight; methylbenzotriazole 0.15–0.35 parts by weight; hindered phenolic antioxidant 0.45–0.80 parts by weight; triphenyl phosphite 0.15–0.40 parts by weight; polyether-modified polysiloxane 0.25–0.55 parts by weight; acetylenic diol nonionic wetting agent 0.15–0.35 parts by weight; low-foaming polyether leveling agent 0.08–0.25 parts by weight; hindered tertiary amine proton scavenger 0.35–0.65 parts by weight; and non-silicone polyether defoamer 0.15–0.40 parts by weight.

7. The method for preparing a surface passivation solder powder no-clean halogen-free solder paste according to claim 5, characterized in that: The acid / amine molar ratio of the succinic acid / N,N-diisopropylethanolamine salt is 1.00:0.95–1.00:1.10, and the acid / base molar ratio of the glutaric acid / 2-methylimidazolium salt is 1.00:0.85–1.00:1.

05. The water content of both salts is no more than 0.15% by mass, the D90 is no greater than 12 μm, the differential scanning calorimetry main thermal transition peak is 130–150 °C, and the initial free acid proportion (based on total acid) is no more than 18%. The acid value of the dodecenyl succinic anhydride-rosin alcohol half ester is 70–115 mg KOH / g, and the residual anhydride group is not higher than 6.0% by mass; the acid / amine molar ratio of the sebacic acid mono-2-hydroxyethyl ester / tributylamine salt is 1.00:0.95–1.00:1.10, the differential scanning calorimetry main thermal transition or dissociation peak is 185–205℃, the moisture content at 25℃ is not higher than 0.12% by mass, and the insoluble matter after filtration is not higher than 0.05% by mass.

8. The method for preparing a surface passivation solder powder no-clean halogen-free solder paste according to claim 6, characterized in that: The preparation of the dual-latency halogen-free flux includes: heating tetrahydrofurfuryl alcohol, dipropylene glycol monomethyl ether, diethylene glycol monobutyl ether, and propylene glycol phenyl ether to 130–138°C under a slight positive pressure of nitrogen; adding hydrogenated rosin glycerol ester at 65–75°C; adding polymerized rosin at 88–96°C; adding terpene phenolic resin and low acid value acrylic resin at 112–122°C and holding for 25–35 minutes; lowering the temperature to 84–88°C and adding dodecenyl succinic anhydride-rosin alcohol half ester and sebacic acid mono-2-hydroxyethyl ester / tributylamine salt; and lowering the temperature to 70–74°C. Add succinic acid / N,N-diisopropylethanolamine salt and glutaric acid / 2-methylimidazolium salt, lower the temperature to 60–65°C, add benzotriazole, methylbenzotriazole, hindered phenolic antioxidant, triphenyl phosphite, polyether-modified polysiloxane, acetylenol nonionic wetting agent, low-foaming polyether leveling agent, hindered tertiary amine proton scavenger and non-silicone polyether defoamer, lower the temperature to 52–56°C, add hydrogenated castor oil micro powder and polyamide wax micro powder, and shear for 60–80 minutes. Then, mill twice with three rollers and degas for 12–20 minutes under 8–12 kPa absolute pressure.

9. The method for preparing a surface passivation solder powder no-clean halogen-free solder paste according to claim 1, characterized in that: During solder paste mixing, the oxygen content in the mixing chamber should not exceed 300 ppm, and the dew point should be below -45°C. The low-shear pre-wetting includes spreading all the double-latent halogen-free flux at the bottom of the mixing cup, adding surface-passivated solder powder at an equivalent shear rate of 12–18 s⁻¹ at 35–45 parts by mass / min, adding powder for 20–24 minutes, and continuing low-shear pre-wetting for 5–8 minutes. The equivalent shear rate for high-shear dispersion is 120–150 s⁻¹, lasting for 8–10 minutes, with a cumulative equivalent shear amount of 6.0 × 10^4–9.0 × 10^4, and the paste temperature should not exceed 24–26°C.

10. The method for preparing a surface passivation solder powder no-clean halogen-free solder paste according to claim 9, characterized in that: The stepped vacuum degassing process involves reducing the equivalent shear rate to 10–15 s⁻¹ and applying vacuum in steps of absolute pressure: 25–35 kPa for 2–4 minutes, 15–20 kPa for 4–6 minutes, and 8–12 kPa for 6–10 minutes. After degassing, the pressure is reduced to atmospheric pressure over 1.5–3.0 minutes with dry nitrogen. The mixed solder paste is then transferred to a light-proof sealed container, and the headspace inside the container is replaced with dry nitrogen 2–4 times. Finally, the mixture is cured at 3–8°C for 24–36 hours.

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