Antioxidant solder powder and method of making same

Abstract

This invention relates to the field of solder powder technology, specifically to an antioxidant solder powder and its preparation method. The solder powder uses SAC305 tin-silver-copper alloy solder powder as a matrix, and its surface has an antioxidant treatment layer formed by segmented anchoring of single-terminated phosphate-based polyether oligomers and spacer regulation by polyethylene glycol monomethyl ether. During preparation, under nitrogen protection, the following steps are performed sequentially: ethyl acetate pre-cleaning, aqueous isopropanol water-limited hydroxylation, two-stage single-terminated phosphate-based polyether anchoring, polyethylene glycol monomethyl ether sacrificial spacer treatment, washing, drying, and sieving. The resulting solder powder exhibits low total oxygen increment after 168 hours of open aging at 40°C and 75% RH. Solder paste made from this powder exhibits low viscosity drift, high spreadability, and low solder joint void ratio, making it suitable for high-reliability electronic assembly solder paste.

Description

Technical Field

[0001] This invention relates to the field of solder powder technology, and in particular to an antioxidant solder powder and its preparation method. Background Technology

[0002] Solder powder is a core material in the field of electronic assembly. Among them, SAC305 tin-silver-copper alloy has become the mainstream choice for lead-free solder due to its moderate melting point and high welding strength. However, this alloy has high surface activity and is prone to reacting with oxygen in the air to form an oxide film. This not only reduces the storage stability of the solder powder but also leads to problems such as viscosity drift of solder paste, poor spreadability, and increased void ratio in solder joints, seriously affecting the reliability of electronic products.

[0003] To address the oxidation problem of solder powder, existing technologies often employ organic coatings for surface treatment. Early anti-oxidation treatments commonly used fatty acids and alkanolamine compounds. While these substances can form a temporary protective layer on the solder powder surface, they have poor high-temperature resistance and are prone to decomposition during reflow soldering, producing volatile substances that can actually exacerbate voids in the solder joints. Furthermore, their residual amount is difficult to control, which can lead to unstable solder paste viscosity and decreased fluidity after storage.

[0004] Subsequent improvements attempted to use polyether compounds as a treatment agent, utilizing their long-chain structure to block oxygen from contacting the solder powder surface. However, because polyethers lack anchoring groups to bind to the solder powder surface, they can only adhere through physical adsorption, making them prone to detachment during storage, and their antioxidant effect rapidly diminishes over time.

[0005] Some studies have enhanced the bonding force between polyether and solder powder through surface hydroxylation treatment. However, existing hydroxylation processes often use high-water-content systems, which can easily lead to excessive oxidation of the solder powder. Furthermore, anchoring treatment often involves adding the anchoring agent in a single step, which can cause uneven anchoring layer thickness and local agglomeration, hindering solder wetting and reducing spreadability. In addition, existing processes often omit the subsequent washing step, resulting in high levels of solvent and unreacted treatment agents, further deteriorating the rheological properties of the solder paste and the quality of the solder joints.

[0006] In summary, existing technologies have consistently failed to achieve a balance between storage oxidation resistance, solder paste rheological stability, spreadability, and low void ratio of solder joints. Each performance aspect is compromised, making it difficult to meet the needs of high-end electronic assembly. Summary of the Invention

[0007] In view of this, the purpose of this invention is to propose an antioxidant solder powder and its preparation method, so as to solve the problems that existing antioxidant solder powders are mostly treated with unanchored polyether, which makes them easy to oxidize during storage, and the solder paste has large viscosity drift, poor spreading and high solder joint void rate, making it difficult to achieve a balance of multiple properties.

[0008] To achieve the above objectives, the present invention provides an antioxidant solder powder, comprising SAC305 tin-silver-copper alloy solder powder and an antioxidant treatment layer on the surface of the SAC305 tin-silver-copper alloy solder powder. The alloy composition of the SAC305 tin-silver-copper alloy solder powder raw material comprises 96.5 wt% tin, 3.0 wt% silver and 0.5 wt% copper, the nominal particle size of the raw material is 20-38 μm, and the initial total oxygen content of the raw material is not higher than 800 mg / kg. The antioxidant treatment layer includes polyether segments formed by phosphate-anchored single-ended phosphate-terminated polyether oligomers and spacer components formed by polyethylene glycol monomethyl ether. The antioxidant solder powder is prepared by sequentially subjecting the following steps: water-limited surface hydroxylation, first-stage anchoring treatment, second-stage anchoring treatment, sacrificial interval treatment, washing, and drying, based on 1000 parts by weight of the SAC305 tin-silver-copper alloy solder powder. The water-limited surface hydroxylation is carried out in an aqueous isopropanol system, which includes 2200-3000 parts by mass of isopropanol and 6-18 parts by mass of water. The first anchoring treatment uses 0.7-1.8 parts by weight of a single-ended phosphate-based polyether oligomer with a number average molecular weight of 800-1500; the second anchoring treatment uses 1.2-3.2 parts by weight of a single-ended phosphate-based polyether oligomer with a number average molecular weight of 800-1500; the single-ended phosphate-based polyether oligomers used in the first and second anchoring treatments can be the same or different. The sacrificial interval treatment uses 2.5-8.0 parts by weight of polyethylene glycol monomethyl ether with a number average molecular weight of 950-1050.

[0009] Preferably, the finished particle size distribution of the antioxidant solder powder satisfies the following: D10 is 20.0-22.5μm, D50 is 28.5-31.5μm, and D90 is 37.0-40.5μm.

[0010] Preferably, the single-terminated phosphate-based polyether oligomer is methoxy polyethylene glycol phosphate, and its structure includes methoxy-terminated polyethylene glycol segments and at least one phosphate-anchored end group.

[0011] Preferably, the total residual solvent content of ethyl acetate and isopropanol in the antioxidant solder powder is not higher than 500 ppm, and the total residual solvent content is determined by headspace gas chromatography.

[0012] Preferably, the antioxidant solder powder is spread in a 1.0 mm powder layer and aged in an open environment at 40°C and 75%RH for 168 h. The average total oxygen increment measured by the reduction-extraction method is not higher than 180 ppm, preferably not higher than 160 ppm.

[0013] Furthermore, the present invention also provides a method for preparing antioxidant solder powder, comprising the following steps: (1) Under nitrogen protection with a dew point not higher than -30℃, SAC305 tin-silver-copper alloy solder powder was pre-cleaned with ethyl acetate and filtered; (2) Add the SAC305 tin-silver-copper alloy solder powder obtained in step (1) to an aqueous isopropanol system for water-limited surface hydroxylation, filter, and enter the first stage of anchoring treatment within 5 minutes after filtration. (3) Add 0.7-1.8 parts by weight of single-ended phosphate polyether oligomer to isopropanol and water to obtain the first anchoring treatment solution; add the SAC305 tin-silver-copper alloy solder powder obtained in step (2) to the first anchoring treatment solution for the first stage of anchoring treatment, and filter. (4) Add 1.2-3.2 parts by weight of single-ended phosphate polyether oligomer to isopropanol, stir and then add ethyl acetate to obtain the second anchoring treatment solution; add the SAC305 tin-silver-copper alloy solder powder obtained in step (3) to the second anchoring treatment solution for the second stage of anchoring treatment. (5) Add 2.5-8.0 parts by weight of polyethylene glycol monomethyl ether to isopropanol, stir to dissolve, cool and add ethyl acetate to obtain a sacrificial spacer treatment solution; add the sacrificial spacer treatment solution to the slurry obtained in step (4) for sacrificial spacer treatment; (6) The slurry obtained in step (5) is filtered, washed sequentially with a mixture of ethyl acetate / isopropanol and ethyl acetate, then dried and sieved under nitrogen protection to obtain antioxidant solder powder.

[0014] Preferably, in step (2), based on 1000 parts by mass of tin-silver-copper solder powder, the aqueous isopropanol system includes 2200-3000 parts by mass of isopropanol and 6-18 parts by mass of water; the temperature of the water-limited surface hydroxylation is 22-30℃, the stirring speed is 90-110 rpm, and the time is 6-12 min; after filtration, it proceeds to step (3) within 5 min.

[0015] Preferably, in step (6), the washing includes: after filtering to remove the liquid phase from the slurry obtained in step (5), adding ethyl acetate and isopropanol to the filtered tin-silver-copper solder powder, stirring at 55-70 rpm for 7-10 min at 25°C, and then filtering; then adding ethyl acetate to the filtered tin-silver-copper solder powder, stirring at 55-70 rpm for 7-10 min at 25°C, and then filtering.

[0016] Preferably, in step (6), the drying and sieving includes: keeping the washed tin-silver-copper solder powder at 48-55°C for 1.5-3 hours under nitrogen protection, and then continuing to dry it at 34-38°C until the residual solvent content is not higher than 500ppm; then lightly sieving it through a 75μm sieve under nitrogen protection, collecting the sieve material to obtain antioxidant solder powder.

[0017] The beneficial effects of this invention are: (1) This invention achieves a stable chemical bond between the antioxidant treatment layer and the surface of tin-silver-copper solder powder through the synergistic effect of water-limited surface hydroxylation and two-stage single-end phosphate polyether anchoring, rather than physical adsorption. Data shows that after 168 hours of open aging at 40°C and 75%RH, the total oxygen increase of the solder powder in Examples 1-6 was only 78-160 ppm, far lower than the 507 ppm of Comparative Example 1 (treated with unanchored polyether), indicating a significant improvement in storage antioxidant effect.

[0018] (2) The two-stage anchoring combined with the sacrificial interval treatment design ensures both the uniformity and density of the anchoring layer and avoids the agglomeration of chain segments caused by excessive anchoring agent. The viscosity drift rate of the solder paste prepared in Examples 1-6 is only 5.6%-8.8%, which is much lower than the 28.6% of Comparative Example 5 (washing step omitted); the spreading rate reaches 86.4%-91.4%, and the average solder joint void rate is only 6.8%-10.8%, which effectively solves the problems of unstable rheology, poor wetting, and high voids in solder paste caused by the antioxidant coating in the prior art.

[0019] (3) The strict washing and residue control process ensures that the residual solvent content of the solder powder is no more than 500 ppm, thus avoiding the impact of solvent residue on solder performance. Among them, Examples 3 and 4 use moderate water-limited hydroxylation strength and anchoring agent dosage, which have the best overall performance. While ensuring the antioxidant effect, they do not significantly increase the thickness of the organic layer, thus achieving a balance between storage stability and application performance. Detailed Implementation

[0020] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments.

[0021] In this invention, water-limited surface hydroxylation refers to the process of making the natural oxide / hydroxyl sites on the surface of solder powder in a system with isopropanol as the main solvent and containing only a small amount of water, so that they can interact with the phosphate anchoring end groups, while controlling the amount of water, the treatment temperature and the treatment time to inhibit the excessive oxidation of the solder powder.

[0022] In this invention, the two-stage anchoring treatment refers to first performing a low-dose single-terminated phosphate-based polyether oligomer in an isopropanol system containing a small amount of water, followed by a second-stage anchoring in an isopropanol / ethyl acetate mixture using a higher-dose single-terminated phosphate-based polyether oligomer. This treatment method is used to reduce localized enrichment and aggregation caused by a one-time addition of the anchoring agent.

[0023] In this invention, the sacrificial spacer treatment refers to adding polyethylene glycol monomethyl ether without phosphate anchoring groups after the second anchoring stage, so that it temporarily occupies the gaps and high-energy adsorption sites of the anchoring layer through hydrogen bonding, van der Waals interactions, or chain segment entanglement; subsequent washing removes the free or weakly adsorbed excess components, leaving only a small amount of spacer components, thereby reducing the increase in solder paste viscosity, decrease in wetting, and obstruction of reflow and venting caused by local enrichment of anchoring agent.

[0024] The raw material sources and specifications are as follows: The tin-silver-copper solder powder is LF-05 SAC305 tin-silver-copper alloy solder powder from Shenzhen BBIEN Technology Co., Ltd., ordered according to Type 4 specifications, with a particle size of 20-38μm. The alloy composition is 96.5wt% tin, 3.0wt% silver, and 0.5wt% copper, with an initial oxygen content not exceeding 800ppm. The single-terminated phosphate polyether oligomers with number average molecular weights of 800, 1000, 1200, and 1500 are all selected from the X-GF-0687 series methoxy polyethylene glycol phosphate from Shaanxi Xinyan Bomei Biotechnology Co., Ltd., with a purity of not less than 95%. Among them, the number average molecular weight of 800... Model X-GF-0687-0.8k has a number average molecular weight of 1000 (model X-GF-0687-1k), model X-GF-0687-1.2k has a number average molecular weight of 1200 (model X-GF-0687-1.2k), and model X-GF-0687-1.5k has a number average molecular weight of 1500. All should be stored at -20℃ in the dark and away from moisture. Polyethylene glycol monomethyl ether is selected from TICE Shanghai Chemical Industry Development Co., Ltd., P2185, with a number average molecular weight of 1000. Example 1:

[0025] Step 1: In a nitrogen-protected environment with a dew point not higher than -30℃, add 1000g of tin-silver-copper solder powder to a glass reaction vessel, purge with nitrogen for 30min, maintain the nitrogen flow rate at 50mL / min, add 2000g of ethyl acetate, stir at 120rpm for 10min at 25℃, and then filter to remove the liquid phase; then add 2000g of ethyl acetate to the filtered tin-silver-copper solder powder, stir at 120rpm for 10min at 25℃, and filter to remove the liquid phase. Step 2: Transfer the tin-silver-copper solder powder obtained in Step 1 into a glass reaction vessel under nitrogen protection, add 2500g isopropanol and 10g ultrapure water, stir at 100rpm for 8min at 25℃, then filter to remove the liquid phase under nitrogen protection, and proceed to Step 3 within 5min. Step 3: Add 1g of single-terminated phosphate polyether oligomer with a number average molecular weight of 1000 to 1500g of isopropanol and 5g of ultrapure water, and stir at 300rpm for 30min at 25℃ to obtain the first anchoring treatment solution; add the tin-silver-copper solder powder obtained in Step 2 to the first anchoring treatment solution, stir at 80rpm for 20min at 25℃, and then filter to remove the liquid phase; Step 4: Add 2g of single-terminated phosphate polyether oligomer with a number average molecular weight of 1000 to 400g of isopropanol, and stir at 300rpm for 30min at 30℃ to obtain a presol; add 600g of ethyl acetate to the presol, and continue stirring at 300rpm for 10min at 30℃ to obtain the second anchoring treatment solution; add the tin-silver-copper solder powder filtered in Step 3 to the second anchoring treatment solution, and stir at 80rpm for 15min at 30℃. Step 5: Add 4g of polyethylene glycol monomethyl ether to 400g of isopropanol, stir at 300rpm for 20min at 45℃, cool to 25℃, add 600g of ethyl acetate, stir at 300rpm for 10min at 25℃ to obtain the sacrificial spacer treatment solution; add the sacrificial spacer treatment solution to the slurry obtained in Step 4, and stir at 60rpm for 10min at 25℃. Step 6: Filter to remove the liquid phase from Step 5, add 1500g ethyl acetate and 500g isopropanol to the filtered tin-silver-copper solder powder, stir at 60rpm for 8min at 25℃ and then filter; then add 2000g ethyl acetate to the filtered tin-silver-copper solder powder, stir at 60rpm for 8min at 25℃ and then filter. Step 7: The tin-silver-copper solder powder obtained in Step 6 is kept at 50°C for 2 hours under nitrogen protection, and then dried at 35°C until the residual solvent content is no more than 500ppm; then it is lightly sieved through a 75μm sieve under nitrogen protection, and the sieve material is collected; every 500g of sieve material is put into an aluminum-plastic composite bag, the gas inside the bag is replaced with nitrogen 3 times, and then it is heat-sealed and stored at below 25°C in the dark to obtain antioxidant solder powder. Example 2:

[0026] Step 1: In a nitrogen-protected environment with a dew point not higher than -30℃, add 1000g of tin-silver-copper solder powder to a glass reaction vessel, purge with nitrogen for 30min, maintain the nitrogen flow rate at 50mL / min, add 1800g of ethyl acetate, stir at 110rpm for 8min at 23℃, and then filter to remove the liquid phase; then add 1800g of ethyl acetate to the filtered tin-silver-copper solder powder, stir at 110rpm for 8min at 23℃, and filter to remove the liquid phase. Step 2: Transfer the tin-silver-copper solder powder obtained in Step 1 into a glass reaction vessel under nitrogen protection, add 2200g isopropanol and 6g ultrapure water, stir at 90rpm for 6min at 22℃, then filter to remove the liquid phase under nitrogen protection, and proceed to Step 3 within 5min. Step 3: Add 0.7g of single-terminated phosphate polyether oligomer with a number average molecular weight of 800 to 1300g of isopropanol and 3g of ultrapure water, and stir at 280rpm for 25min at 22℃ to obtain the first anchoring treatment solution; add the tin-silver-copper solder powder obtained in Step 2 to the first anchoring treatment solution, stir at 70rpm for 15min at 22℃, and then filter to remove the liquid phase; Step 4: Add 1.2g of single-terminated phosphate polyether oligomer with a number average molecular weight of 800 to 350g of isopropanol, and stir at 280rpm for 25min at 28℃ to obtain a presol; add 500g of ethyl acetate to the presol, and continue stirring at 280rpm for 8min at 28℃ to obtain the second anchoring treatment solution; add the tin-silver-copper solder powder filtered in Step 3 to the second anchoring treatment solution, and stir at 70rpm for 12min at 28℃. Step 5: Add 2.5g of polyethylene glycol monomethyl ether to 350g of isopropanol, stir at 280rpm for 18min at 42℃, cool to 25℃, add 500g of ethyl acetate, stir at 280rpm for 8min at 25℃ to obtain the sacrificial spacer treatment solution; add the sacrificial spacer treatment solution to the slurry obtained in Step 4, and stir at 55rpm for 8min at 25℃. Step 6: Filter to remove the liquid phase from Step 5, add 1300g ethyl acetate and 400g isopropanol to the filtered tin-silver-copper solder powder, stir at 55rpm for 7min at 25℃ and then filter; then add 1800g ethyl acetate to the filtered tin-silver-copper solder powder, stir at 55rpm for 7min at 25℃ and then filter. Step 7: The tin-silver-copper solder powder obtained in Step 6 is kept at 48°C for 1.5 hours under nitrogen protection, and then dried at 34°C until the residual solvent content is no higher than 500 ppm; then it is lightly sieved through a 75 μm sieve under nitrogen protection, and the sieve material is collected; every 500g of sieve material is put into an aluminum-plastic composite bag, the gas inside the bag is replaced with nitrogen 3 times, and then it is heat-sealed and stored at below 25°C in the dark to obtain antioxidant solder powder. Example 3:

[0027] Step 1: In a nitrogen-protected environment with a dew point not higher than -30℃, add 1000g of tin-silver-copper solder powder to a glass reaction vessel, purge with nitrogen for 30min, maintain the nitrogen flow rate at 50mL / min, add 2200g of ethyl acetate, stir at 120rpm for 10min at 26℃, and then filter to remove the liquid phase; then add 2200g of ethyl acetate to the filtered tin-silver-copper solder powder, stir at 120rpm for 10min at 26℃, and filter to remove the liquid phase. Step 2: Transfer the tin-silver-copper solder powder obtained in Step 1 into a glass reaction vessel under nitrogen protection, add 2400g isopropanol and 8g ultrapure water, stir at 100rpm for 7min at 24℃, then filter to remove the liquid phase under nitrogen protection, and proceed to Step 3 within 5min. Step 3: Add 0.9g of single-ended phosphate polyether oligomer with a number average molecular weight of 1000 to 1450g of isopropanol and 4g of ultrapure water, and stir at 300rpm for 28min at 24℃ to obtain the first anchoring treatment solution; add the tin-silver-copper solder powder obtained in Step 2 to the first anchoring treatment solution, stir at 80rpm for 18min at 24℃, and then filter to remove the liquid phase; Step 4: Add 1.6g of single-terminated phosphate polyether oligomer with a number average molecular weight of 1000 to 380g of isopropanol, and stir at 300rpm for 28min at 30℃ to obtain a presol; add 550g of ethyl acetate to the presol, and continue stirring at 300rpm for 10min at 30℃ to obtain the second anchoring treatment solution; add the tin-silver-copper solder powder filtered in Step 3 to the second anchoring treatment solution, and stir at 80rpm for 14min at 30℃. Step 5: Add 3.5g of polyethylene glycol monomethyl ether to 380g of isopropanol, stir at 300rpm for 20min at 45℃, cool to 25℃, add 550g of ethyl acetate, stir at 300rpm for 10min at 25℃ to obtain the sacrificial spacer treatment solution; add the sacrificial spacer treatment solution to the slurry obtained in Step 4, stir at 60rpm for 9min at 25℃; Step 6: Filter to remove the liquid phase from Step 5, add 1400g ethyl acetate and 450g isopropanol to the filtered tin-silver-copper solder powder, stir at 60rpm for 8min at 25℃ and then filter; then add 1900g ethyl acetate to the filtered tin-silver-copper solder powder, stir at 60rpm for 8min at 25℃ and then filter. Step 7: The tin-silver-copper solder powder obtained in Step 6 is kept at 50°C for 2 hours under nitrogen protection, and then dried at 35°C until the residual solvent content is no more than 500ppm; then it is lightly sieved through a 75μm sieve under nitrogen protection, and the sieve material is collected; every 500g of sieve material is put into an aluminum-plastic composite bag, the gas inside the bag is replaced with nitrogen 3 times, and then it is heat-sealed and stored at below 25°C in the dark to obtain antioxidant solder powder. Example 4:

[0028] Step 1: In a nitrogen-protected environment with a dew point not higher than -30℃, add 1000g of tin-silver-copper solder powder to a glass reaction vessel, purge with nitrogen for 30min, maintain the nitrogen flow rate at 50mL / min, add 2000g of ethyl acetate, stir at 120rpm for 10min at 25℃, and then filter to remove the liquid phase; then add 2000g of ethyl acetate to the filtered tin-silver-copper solder powder, stir at 120rpm for 10min at 25℃, and filter to remove the liquid phase. Step 2: Transfer the tin-silver-copper solder powder obtained in Step 1 into a glass reaction vessel under nitrogen protection, add 2600g isopropanol and 12g ultrapure water, stir at 100rpm for 9min at 26℃, then filter to remove the liquid phase under nitrogen protection, and proceed to Step 3 within 5min. Step 3: Add 1.2g of single-terminated phosphate polyether oligomer with a number average molecular weight of 1200 to 1600g of isopropanol and 6g of ultrapure water, and stir at 320rpm for 30min at 26℃ to obtain the first anchoring treatment solution; add the tin-silver-copper solder powder obtained in Step 2 to the first anchoring treatment solution, stir at 80rpm for 22min at 26℃, and then filter to remove the liquid phase; Step 4: Add 2.4g of single-terminated phosphate polyether oligomer with a number average molecular weight of 1200 to 450g of isopropanol, and stir at 320rpm for 30min at 32℃ to obtain a presol; add 650g of ethyl acetate to the presol, and continue stirring at 320rpm for 10min at 32℃ to obtain the second anchoring treatment solution; add the tin-silver-copper solder powder filtered in Step 3 to the second anchoring treatment solution, and stir at 80rpm for 16min at 32℃. Step 5: Add 5.0g of polyethylene glycol monomethyl ether to 450g of isopropanol, stir at 320rpm for 20min at 46℃, cool to 25℃, add 650g of ethyl acetate, stir at 320rpm for 10min at 25℃ to obtain the sacrificial spacer treatment solution; add the sacrificial spacer treatment solution to the slurry obtained in Step 4, and stir at 60rpm for 11min at 25℃. Step 6: Filter to remove the liquid phase from Step 5, add 1600g ethyl acetate and 500g isopropanol to the filtered tin-silver-copper solder powder, stir at 60rpm for 8min at 25℃ and then filter; then add 2100g ethyl acetate to the filtered tin-silver-copper solder powder, stir at 60rpm for 8min at 25℃ and then filter. Step 7: The tin-silver-copper solder powder obtained in Step 6 is kept at 52°C for 2.5 hours under nitrogen protection, and then dried at 35°C until the residual solvent content is no higher than 500ppm; then it is lightly sieved through a 75μm sieve under nitrogen protection, and the sieve material is collected; every 500g of sieve material is put into an aluminum-plastic composite bag, the gas inside the bag is replaced with nitrogen 3 times, and then it is heat-sealed and stored at below 25°C in the dark to obtain antioxidant solder powder. Example 5:

[0029] Step 1: In a nitrogen-protected environment with a dew point not higher than -30℃, add 1000g of tin-silver-copper solder powder to a glass reaction vessel, purge with nitrogen for 30min, maintain the nitrogen flow rate at 50mL / min, add 2200g of ethyl acetate, stir at 130rpm for 12min at 27℃, and then filter to remove the liquid phase; then add 2200g of ethyl acetate to the filtered tin-silver-copper solder powder, stir at 130rpm for 12min at 27℃, and filter to remove the liquid phase. Step 2: Transfer the tin-silver-copper solder powder obtained in Step 1 into a glass reaction vessel under nitrogen protection, add 2800g isopropanol and 16g ultrapure water, stir at 110rpm for 11min at 28℃, then filter to remove the liquid phase under nitrogen protection, and proceed to Step 3 within 5min. Step 3: Add 1.5g of single-terminated phosphate polyether oligomer with a number average molecular weight of 1500 to 1750g of isopropanol and 8g of ultrapure water, and stir at 320rpm for 32min at 28℃ to obtain the first anchoring treatment solution; add the tin-silver-copper solder powder obtained in Step 2 to the first anchoring treatment solution, stir at 85rpm for 25min at 28℃, and then filter to remove the liquid phase; Step 4: Add 3.0 g of single-terminated phosphate polyether oligomer with a number average molecular weight of 1500 to 550 g of isopropanol, and stir at 320 rpm for 32 min at 34 °C to obtain a pre-solution; add 750 g of ethyl acetate to the pre-solution, and continue stirring at 320 rpm for 12 min at 34 °C to obtain the second anchoring treatment solution; add the tin-silver-copper solder powder filtered in Step 3 to the second anchoring treatment solution, and stir at 85 rpm for 18 min at 34 °C. Step 5: Add 7.0 g of polyethylene glycol monomethyl ether to 550 g of isopropanol, stir at 320 rpm for 22 min at 48 °C, cool to 25 °C, add 750 g of ethyl acetate, stir at 320 rpm for 12 min at 25 °C to obtain the sacrificial spacer treatment solution; add the sacrificial spacer treatment solution to the slurry obtained in Step 4, and stir at 65 rpm for 12 min at 25 °C. Step 6: Filter to remove the liquid phase from Step 5, add 1800g ethyl acetate and 600g isopropanol to the filtered tin-silver-copper solder powder, stir at 65rpm for 10min at 25℃ and then filter; then add 2200g ethyl acetate to the filtered tin-silver-copper solder powder, stir at 65rpm for 10min at 25℃ and then filter. Step 7: The tin-silver-copper solder powder obtained in Step 6 is kept at 54°C for 3 hours under nitrogen protection, and then dried at 36°C until the residual solvent content is no more than 500ppm; then it is lightly sieved through a 75μm sieve under nitrogen protection, and the sieve material is collected; every 500g of sieve material is put into an aluminum-plastic composite bag, the gas inside the bag is replaced with nitrogen 3 times, and then it is heat-sealed and stored at below 25°C in the dark to obtain antioxidant solder powder. Example 6:

[0030] Step 1: In a nitrogen-protected environment with a dew point not higher than -30℃, add 1000g of tin-silver-copper solder powder to a glass reaction vessel, purge with nitrogen for 30min, maintain the nitrogen flow rate at 50mL / min, add 2000g of ethyl acetate, stir at 120rpm for 10min at 25℃, and then filter to remove the liquid phase; then add 2000g of ethyl acetate to the filtered tin-silver-copper solder powder, stir at 120rpm for 10min at 25℃, and filter to remove the liquid phase. Step 2: Transfer the tin-silver-copper solder powder obtained in Step 1 into a glass reaction vessel under nitrogen protection, add 3000g isopropanol and 18g ultrapure water, stir at 110rpm for 12min at 30℃, then filter to remove the liquid phase under nitrogen protection, and proceed to Step 3 within 5min. Step 3: Add 1.8g of single-terminated phosphate polyether oligomer with a number average molecular weight of 1000 to 1800g of isopropanol and 10g of ultrapure water, and stir at 350rpm for 35min at 30℃ to obtain the first anchoring treatment solution; add the tin-silver-copper solder powder obtained in Step 2 to the first anchoring treatment solution, stir at 90rpm for 28min at 30℃, and then filter to remove the liquid phase; Step 4: Add 3.2g of single-terminated phosphate polyether oligomer with a number average molecular weight of 1000 to 600g of isopropanol, and stir at 350rpm for 35min at 35℃ to obtain a presol; add 800g of ethyl acetate to the presol, and continue stirring at 350rpm for 12min at 35℃ to obtain the second anchoring treatment solution; add the tin-silver-copper solder powder filtered in Step 3 to the second anchoring treatment solution, and stir at 90rpm for 20min at 35℃. Step 5: Add 8.0g of polyethylene glycol monomethyl ether to 600g of isopropanol, stir at 350rpm for 25min at 50℃, cool to 25℃, add 800g of ethyl acetate, stir at 350rpm for 12min at 25℃ to obtain the sacrificial spacer treatment solution; add the sacrificial spacer treatment solution to the slurry obtained in Step 4, stir at 70rpm for 15min at 25℃; Step 6: Filter to remove the liquid phase from Step 5, add 2000g ethyl acetate and 700g isopropanol to the filtered tin-silver-copper solder powder, stir at 70rpm for 10min at 25℃ and then filter; then add 2400g ethyl acetate to the filtered tin-silver-copper solder powder, stir at 70rpm for 10min at 25℃ and then filter. Step 7: The tin-silver-copper solder powder obtained in Step 6 is kept at 55°C for 3 hours under nitrogen protection, and then dried at 38°C until the residual solvent content is no higher than 500ppm; then it is lightly sieved through a 75μm sieve under nitrogen protection, and the sieve material is collected; every 500g of sieve material is put into an aluminum-plastic composite bag, the gas inside the bag is replaced with nitrogen 3 times, and then it is heat-sealed and stored below 25°C in the dark to obtain antioxidant solder powder.

[0031] Comparative Example 1: The difference from Example 1 is that in step 3, instead of adding 1g of single-ended phosphate polyether oligomer with a number average molecular weight of 1000, 1g of polyethylene glycol monomethyl ether is added; in step 4, instead of adding 2g of single-ended phosphate polyether oligomer with a number average molecular weight of 1000, 2g of polyethylene glycol monomethyl ether is added; the other conditions are the same as in Example 1.

[0032] Comparative Example 2: The difference from Example 1 is that 10g of ultrapure water is not added in step 2, and the amount of isopropanol is adjusted from 2500g to 2510g; the other conditions are the same as in Example 1.

[0033] Comparative Example 3: The difference from Example 1 is as follows: In step 3, the number-average molecular weight 1000 single-ended phosphate-based polyether oligomer was adjusted to 3g and added to 1500g isopropanol and 5g ultrapure water. After stirring at 300rpm for 30min at 25°C, a primary anchoring solution was obtained. The tin-silver-copper solder powder obtained in step 2 was added to the primary anchoring solution and stirred at 80rpm for 20min at 25°C. Subsequently, without filtering in step 3, 400g isopropanol and 600g ethyl acetate used in step 4 of Example 1 were directly added, and stirring was continued at 80rpm for 15min at 30°C. In step 4, the number-average molecular weight 1000 single-ended phosphate-based polyether oligomer was not added separately. The other conditions were the same as in Example 1.

[0034] Comparative Example 4: The difference from Example 1 is that 4g of polyethylene glycol monomethyl ether is not added in step 5, and 4g of ethyl acetate is added to maintain the total mass of the liquid phase in this step consistent with that in Example 1; the other conditions are the same as in Example 1.

[0035] Comparative Example 5: The difference from Example 1 is that in step 6, the first wash with 1500g ethyl acetate and 500g isopropanol is not performed, nor is the second wash with 2000g ethyl acetate. Instead, the slurry obtained in step 5 is filtered and directly enters step 7. The other conditions are the same as in Example 1.

[0036] Comparative Example 6: The difference from Example 1 is that the single-ended phosphate polyether oligomers in steps 3 and 4 are both single-ended phosphate polyether oligomers with a number average molecular weight of 500, and the amounts are still 1g and 2g respectively; the other conditions are the same as in Example 1.

[0037] Comparative Example 7: The difference from Example 1 is that the single-ended phosphate polyether oligomers in steps 3 and 4 are both single-ended phosphate polyether oligomers with a number average molecular weight of 3000, and the amounts are still 1g and 2g respectively; the other conditions are the same as in Example 1.

[0038] Comparative Example 8: The difference from Example 1 is that the amount of single-ended phosphate polyether oligomer with a number average molecular weight of 1000 in step 3 is adjusted from 1g to 2g, and the amount of single-ended phosphate polyether oligomer with a number average molecular weight of 1000 in step 4 is adjusted from 2g to 8g; the other conditions are the same as in Example 1.

[0039] Performance testing: Sample Preparation: Solder powders obtained in Examples 1-6 and Comparative Examples 1-8 were used as test samples. After preparation, each sample was stored at below 25°C in the dark for 24 hours, and then divided into intrinsic powder characterization samples and solder paste application performance samples. Intrinsic powder characterization samples were directly used for particle size and total oxygen content testing. Solder paste application performance samples were prepared according to the ratio of 88.5 wt% solder powder and 11.5 wt% no-clean flux base material from the same batch. 88.5 g of solder powder and 11.5 g of no-clean flux base material were placed in a vacuum planetary mixer, stirred at 800 rpm for 4 min at 25°C, and then stirred at 1500 rpm for 2 min, while simultaneously evacuating to an absolute pressure not exceeding 5 kPa. After stirring, the mixture was sealed and allowed to stand at 25°C for 4 hours to obtain the solder paste test samples of the corresponding examples and comparative examples.

[0040] Powder particle size testing: The particle size distribution of the solder powder obtained in Examples 1-6 and Comparative Examples 1-8 was tested according to GB / T 19077-2024 "Particle Size Analysis by Laser Diffraction". For each sample, 0.10 g of solder powder was added to 50 mL of isopropanol and dispersed under ultrasonic conditions at 100 W for 60 s. Immediately afterwards, the powder was added to the circulating chamber of a laser particle size analyzer. The shading rate was controlled at 10%-15%, the circulation speed was set to 2000 rpm, and the test temperature was 25℃. Each sample was tested in triplicate, and D10, D50, and D90 were recorded.

[0041] Total oxygen content and oxygen increment after storage: The total oxygen content of the solder powder was tested according to GB / T 5158.1-2011 "Determination of Oxygen Content by Reduction Method of Metal Powders Part 1: General Rules" and GB / T 5158.4-2011 "Determination of Oxygen Content by Reduction Method of Metal Powders Part 4: Determination of Total Oxygen by Reduction-Extraction Method". Two portions were prepared for each sample. One portion was tested directly for its initial total oxygen content 24 hours after preparation. The other portion was spread evenly in a clean glass dish with a powder layer thickness controlled at 1.0 mm and aged in an open-air temperature and humidity chamber at 40℃ and 75%RH for 168 hours. After aging, it was immediately cooled to 25℃ in a nitrogen-protected bag, and the total oxygen content after aging was tested. 0.50 g of solder powder was weighed for each test, and the graphite crucible reduction-extraction method was used. The instrument was calibrated with blank samples and standard samples. Each sample was tested in parallel three times. The total oxygen increment was obtained by subtracting the initial total oxygen content from the total oxygen content after aging.

[0042] Solder paste viscosity drift test: The viscosity stability of solder paste samples prepared from various solder powders was tested according to SJ / T 11186-2019 "General Specification for Solder Paste" and GB / T 31475-2015 "Solder Paste for High-Quality Internal Interconnection in Electronic Assembly". Each solder paste sample was equilibrated at 25℃ for 4 hours and then sampled. A rotational viscometer was used at 25.0℃ and 10 rpm. After the rotor was immersed in the sample, a pre-shear was applied for 60 seconds, followed by continuous testing for 300 seconds, and the stable reading was recorded as the initial viscosity. Another sample of the same type was placed in a sealed container at 25℃ for 24 hours, and the viscosity after this period was tested under the same conditions. The viscosity drift rate was calculated by dividing the absolute value of the difference between the viscosity after this period and the initial viscosity by the initial viscosity and then multiplying by 100%.

[0043] Spreadability Test: The reflow spreadability of each solder paste sample was evaluated according to the extended test method in SJ / T 11390-2019 "Test Methods for Lead-Free Solder". An oxygen-free copper sheet with dimensions of 40mm × 40mm × 0.30mm was used as the substrate. The copper sheet was first sanded 10 times in the same direction with 1000-grit sandpaper, then wiped 3 times with ethyl acetate and dried at 25℃ for 10 minutes. A 0.20mm thick stainless steel mesh with a 6.50mm diameter hole was fixed to the surface of the copper sheet. After printing the solder paste, the mesh was removed to obtain the initial circular solder paste pattern. Reflow soldering was performed in an air atmosphere. The preheating zone was heated from 25℃ to 150℃ in 90 seconds, held at 150-180℃ for 80 seconds, and held above 217℃ for 60 seconds. The peak temperature was 245℃, and the cooling rate was 3℃ / s. After reflow, the solder spreading area was measured using image analysis software. The spreading rate was calculated by dividing the reflow solder spreading area by the initial stencil area and then multiplying by 100%. Five points were tested for each sample, and the average value was taken.

[0044] Solder joint void rate test: The void rate of each solder paste sample after solder joint formation was evaluated according to GB / T 19247.6-2024 "Printed Circuit Board Assembly - Part 6: Evaluation Requirements and Test Methods for Solder Joint Voids in Ball Grid Arrays (BGAs) and Disk Grid Arrays (LGAs)". A gold-plated disk grid array test board was used. The test area was a 10×10 pad array with a pad diameter of 0.30 mm and a pad spacing of 0.50 mm. Solder paste was printed on a 0.10 mm thick stainless steel mesh with an opening diameter of 0.28 mm. The corresponding disk grid array test elements were mounted with a mounting pressure of 1.5 N, and reflow was completed within 30 minutes after mounting. The reflow profile was the same as that for the spread rate test. After reflow, X-ray inspection equipment was used for testing. The tube voltage was 90kV, the tube current was 100μA, and the magnification was 80x. Five boards were tested for each sample. Twenty-five solder joints in the central area of ​​each board were selected for statistical analysis. The percentage of void area in each solder joint relative to the projected area of ​​the solder joint was calculated, and the average void rate of the solder joint was calculated.

[0045] Table 1 Performance Test Results As shown in Table 1, in Comparative Example 1, after replacing the single-terminated phosphate-based polyether oligomer with polyethylene glycol monomethyl ether, there was a lack of anchoring end groups that could directionally bind to the oxidation / hydroxyl sites on the surface of tin-silver-copper solder powder. After aging, the total oxygen increase reached 507 ppm, the solder paste viscosity drift rate was 20.5%, the spreading rate was only 80.4%, and the average solder joint void rate was 16.8%. This indicates that simply introducing polyethers without anchoring end groups is difficult to simultaneously achieve both storage anti-oxidation and reflow wetting.

[0046] Comparative Example 2 did not undergo water-limited surface hydroxylation. Although single-terminated phosphate polyether oligomers were still added, the total oxygen increment after aging increased to 341 ppm, indicating that the lack of controlled hydroxylation would weaken the effectiveness of subsequent anchoring treatment. Comparative Example 3 changed the two-stage anchoring to one-stage anchoring, Comparative Example 4 eliminated the sacrificial interval treatment, and Comparative Example 5 eliminated subsequent washing. Its oxygen increment, viscosity drift rate, spreading rate, and void ratio were all significantly worse than those of Example 1, indicating that water-limited hydroxylation, segmented anchoring, sacrificial interval, and washing residue control have a synergistic effect.

[0047] Examples 1-6, while maintaining the particle size distribution characteristics of Type 4 solder powder, showed that the total oxygen increment after aging was controlled at 78-160 ppm, the viscosity drift rate was controlled at 5.6%-8.8%, the spreading rate was 86.4%-91.4%, and the average solder joint void rate was 6.8%-10.8%. Among them, Examples 3 and 4 showed better overall performance, indicating that moderate water-limited hydroxylation intensity, appropriate molecular weight of single-terminated phosphate polyether oligomers, and segmented anchoring dosage are more conducive to inhibiting further oxidation of the powder surface without significantly increasing the organic residue burden.

[0048] Examples 5 and 6, due to their higher molecular weight or treatment intensity, still exhibited better antioxidant performance than most comparative examples, but their spreadability and void ratio decreased slightly, presumably due to the thicker surface organic layer or restricted chain migration. Comparative examples 7 and 8 further illustrate that although excessively high molecular weight or excessive anchoring agent can reduce oxygen increment to some extent, it will increase particle size tail end, viscosity drift, and reflow wetting resistance.

[0049] In summary, this invention achieves a better balance between solder powder's antioxidant properties during storage, the rheological stability of solder paste, spreadability, and low voids in solder joints through a continuous process of water-limited hydroxylation, two-stage single-terminal phosphate polyether anchoring, polyethylene glycol monomethyl ether sacrificial interval, and thorough washing to control residues. Compared with solutions that use no anchoring polyether, eliminate water-limited hydroxylation, perform one-time anchoring, or eliminate washing, this invention demonstrates a more significant synergistic effect.

[0050] Those skilled in the art should understand that the discussion of any of the above embodiments is merely exemplary and is not intended to imply that the scope of the invention is limited to these examples; within the framework of the invention, the technical features of the above embodiments or different embodiments can also be combined, and there are many other variations of the different aspects of the invention as described above, which are not provided in detail for the sake of brevity.

Claims

1. An antioxidant solder powder, comprising SAC305 tin-silver-copper alloy solder powder and an antioxidant treatment layer on the surface of the SAC305 tin-silver-copper alloy solder powder, characterized in that, The SAC305 tin-silver-copper alloy solder powder raw material has an alloy composition of 96.5 wt% tin, 3.0 wt% silver and 0.5 wt% copper, a nominal particle size of 20-38 μm, and an initial total oxygen content of no more than 800 mg / kg. The antioxidant treatment layer includes polyether segments formed by phosphate-anchored single-ended phosphate-based polyether oligomers and spacer components formed by polyethylene glycol monomethyl ether. The antioxidant solder powder is prepared by sequentially subjecting the following steps: water-limited surface hydroxylation, first-stage anchoring treatment, second-stage anchoring treatment, sacrificial interval treatment, washing, and drying, based on 1000 parts by weight of the SAC305 tin-silver-copper alloy solder powder. The water-limited surface hydroxylation is carried out in an aqueous isopropanol system, which includes 2200-3000 parts by mass of isopropanol and 6-18 parts by mass of water. The first anchoring treatment uses 0.7-1.8 parts by weight of a single-ended phosphate-based polyether oligomer with a number average molecular weight of 800-1500; the second anchoring treatment uses 1.2-3.2 parts by weight of a single-ended phosphate-based polyether oligomer with a number average molecular weight of 800-1500; the single-ended phosphate-based polyether oligomers used in the first and second anchoring treatments can be the same or different. The sacrificial interval treatment uses 2.5-8.0 parts by weight of polyethylene glycol monomethyl ether with a number average molecular weight of 950-1050.

2. The antioxidant solder powder according to claim 1, characterized in that, The finished particle size distribution of the antioxidant solder powder meets the following requirements: D10 is 20.0-22.5μm, D50 is 28.5-31.5μm, and D90 is 37.0-40.5μm.

3. The antioxidant solder powder according to claim 1, characterized in that, The single-terminated phosphate-based polyether oligomer is a methoxy polyethylene glycol phosphate, the structure of which includes methoxy-terminated polyethylene glycol segments and at least one phosphate-anchored end group.

4. The antioxidant solder powder according to claim 1, characterized in that, The total residual solvent content of ethyl acetate and isopropanol in the antioxidant solder powder is not higher than 500 ppm, and the total residual solvent content is determined by headspace gas chromatography.

5. The antioxidant solder powder according to claim 1, characterized in that, The antioxidant solder powder is spread in a 1.0 mm thick powder layer and aged in an open environment at 40°C and 75%RH for 168 h. The average total oxygen increment measured by the reduction-extraction method is not higher than 180 ppm, preferably not higher than 160 ppm.

6. A method for preparing antioxidant solder powder according to any one of claims 1-5, characterized in that, Includes the following steps: (1) Under nitrogen protection with a dew point not higher than -30℃, SAC305 tin-silver-copper alloy solder powder was pre-cleaned with ethyl acetate and filtered; (2) Add the SAC305 tin-silver-copper alloy solder powder obtained in step (1) to an aqueous isopropanol system for water-limited surface hydroxylation, filter, and enter the first stage of anchoring treatment within 5 minutes after filtration. (3) Add 0.7-1.8 parts by weight of single-ended phosphate polyether oligomer to isopropanol and water to obtain the first anchoring treatment solution; add the SAC305 tin-silver-copper alloy solder powder obtained in step (2) to the first anchoring treatment solution for the first stage of anchoring treatment, and filter. (4) Add 1.2-3.2 parts by weight of single-ended phosphate polyether oligomer to isopropanol, stir and then add ethyl acetate to obtain the second anchoring treatment solution; add the SAC305 tin-silver-copper alloy solder powder obtained in step (3) to the second anchoring treatment solution for the second stage of anchoring treatment. (5) Add 2.5-8.0 parts by weight of polyethylene glycol monomethyl ether to isopropanol, stir to dissolve, cool and add ethyl acetate to obtain a sacrificial spacer treatment solution; add the sacrificial spacer treatment solution to the slurry obtained in step (4) for sacrificial spacer treatment; (6) The slurry obtained in step (5) is filtered, washed sequentially with a mixture of ethyl acetate / isopropanol and ethyl acetate, then dried and sieved under nitrogen protection to obtain antioxidant solder powder.

7. The method for preparing antioxidant solder powder according to claim 6, characterized in that, In step (2), based on 1000 parts by mass of tin-silver-copper solder powder, the aqueous isopropanol system includes 2200-3000 parts by mass of isopropanol and 6-18 parts by mass of water; the temperature of the water-limited surface hydroxylation is 22-30℃, the stirring speed is 90-110 rpm, and the time is 6-12 min; after filtration, it proceeds to step (3) within 5 min.

8. The method for preparing antioxidant solder powder according to claim 6, characterized in that, In step (6), the washing includes: after filtering to remove the liquid phase from the slurry obtained in step (5), adding ethyl acetate and isopropanol to the filtered tin-silver-copper solder powder, stirring at 55-70 rpm for 7-10 min at 25°C, and then filtering; then adding ethyl acetate to the filtered tin-silver-copper solder powder, stirring at 55-70 rpm for 7-10 min at 25°C, and then filtering.

9. The method for preparing antioxidant solder powder according to claim 6, characterized in that, In step (6), the drying and sieving include: keeping the washed tin-silver-copper solder powder at 48-55℃ for 1.5-3h under nitrogen protection, and then continuing to dry it at 34-38℃ until the residual solvent content is not higher than 500ppm; then lightly sieving it through a 75μm sieve under nitrogen protection, collecting the sieve material to obtain antioxidant solder powder.

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