Additive for co-deposition of tin-bismuth alloy as well as preparation method and application of additive

Abstract

The invention discloses an additive for co-deposition of tin-bismuth alloy and a preparation method and application of the additive, and relates to the technical field of electroplating additives and electronic solder. Wherein the additive is polyether quaternary ammonium salt formed by reaction of polyepichlorohydrin and a tertiary amine compound; wherein the tertiary amine compound is selected from one or more of 3-dimethylamino-1-propyl alcohol, N, N-dimethyl butylamine and 1-methylimidazole. The additive can form a compact protective film on the surface of electroplated metal, effectively solves the common problem of hydrogen evolution in an electroplating link, and improves the quality of a plating layer and the electroplating stability. Meanwhile, according to the electroplating liquid containing the additive, the additive and the coordination agent in the electroplating liquid can play a synergistic role in the electroplating process, the precipitation potential difference of Sn < 2 + > and Bi < 3 + > is remarkably reduced, and therefore efficient co-deposition of the two metal ions is achieved, and the component uniformity and performance stability of a plating layer are guaranteed.

Description

Technical Field

[0001] This invention relates to the field of electroplating additives and electronic solder technology, and particularly to an additive for co-depositing tin-bismuth alloys, its preparation method and application. Background Technology

[0002] In electronic solder systems, tin-bismuth alloy (Sn-Bi) solder is widely used in flexible electronics, automotive electronics, advanced semiconductor packaging and other fields due to its advantages such as stable melting point (138℃), low welding temperature (150~170℃) and high adhesion, meeting diverse application needs.

[0003] The fabrication processes for Sn-Bi solder joints vary depending on the application requirements: Bulk solder preparation involves mixing Sn and Bi in a specific ratio, heating and melting them, and then stamping them into sheets, with a minimum fabrication size of approximately 1 mm. Solder paste preparation involves thoroughly mixing the prepared Sn and Bi raw materials with an atomizing agent and a mixing agent, followed by drying. The size of solder joints formed through stencil printing is limited by the processing precision of the stencil. Electroplating, on the other hand, utilizes a redox reaction to electrodeposit a Sn-Bi solder layer on the substrate surface. This process allows for precise fabrication based on customized patterns on the substrate. In contrast, bulk solder stamping and solder paste stencil printing processes are insufficient to meet the current high-integration packaging array requirements for tiny solder joints smaller than 10 μm, while electroplating offers the feasibility of achieving this small size target.

[0004] However, the use of Sn-Bi electrodeposition solder for encapsulation welding technology still has drawbacks: (1) During Sn-Bi electroplating, due to the different deposition potentials of metallic Sn and metallic Bi, it is difficult to control the content of each component in the electroplated layer; (2) During Sn-Bi electroplating, hydrogen evolution reaction is prone to occur. 2+ Bi 3+ The deposition potential and hydrogen ion (H) + The reduction potentials of the cathode and cathode are relatively close, and local alkaline regions are easily formed on the cathode surface. Therefore, hydrogen evolution reaction, in which hydrogen ions gain electrons to generate hydrogen gas, is easily accompanied, resulting in a loose structure of the electroplated layer.

[0005] Among the currently published relevant patents, the solutions to the above two problems all adopt differentiated process routes, but they generally have limitations in terms of cost or environmental protection: Firstly, patent ZL202311247670.9 uses cyanide-free electroplating technology to achieve Sn-Bi electroplating. Its electroplating additive system includes gelatin, disodium EDTA, polyethylene glycol (all three acting as coordination agents), and catechol (as an antioxidant), and requires a pulsed power supply to complete Sn-Bi co-deposition. This scheme not only uses as many as four types of additives but also relies on specific pulsed power supply equipment, resulting in significantly higher overall costs in engineering applications. Similarly, patent ZL202410816532.6 also suffers from similar problems, with excessive additive usage driving up actual application costs.

[0006] Secondly, although patent ZL202380012687.8 takes a different approach by using acids such as nitric acid and sulfuric acid as the first reagent and imine substances as the second reagent, and changes the electroplating potential by regulating the coordination morphology of Bi ions to achieve Sn-Bi co-deposition; at the same time, it uses a self-developed "hydrophilic end-hydrophobic tail" structured organic molecule to inhibit the hydrogen evolution reaction, the additives used in this scheme belong to the category of heavy pollutants, which is contrary to the current green and environmentally friendly industrial development needs and poses obvious environmental risks.

[0007] Therefore, existing technologies still need improvement and development. Summary of the Invention

[0008] In view of the shortcomings of the prior art, the purpose of this invention is to provide an additive for co-depositing tin-bismuth alloys, its preparation method and application, aiming to solve the hydrogen evolution problem commonly encountered in the existing Sn-Bi electroplating process, improve the quality of the electroplated solder layer, make it suitable for packaging soldering, and take into account both cost optimization and environmental protection requirements.

[0009] The technical solution of the present invention is as follows: In a first aspect, an additive for co-depositing tin-bismuth alloys is provided, said additive being a polyether quaternary ammonium salt formed by the reaction of polyepoxychloropropane and a tertiary amine compound; The tertiary amine compound is selected from one or more of 3-dimethylamino-1-propanol, N,N-dimethylbutylamine, and 1-methylimidazole.

[0010] In a preferred embodiment, the additive is selected from one of the following structures: ; Where n and p are independently selected from natural numbers from 0 to 45, and the sum of n and p is from 20 to 100.

[0011] In a preferred embodiment, the molar ratio of the polyepoxychloropropane to the tertiary amine compound is 1:(0.05~5).

[0012] In a preferred embodiment, the polyepoxychloropropane has a weight-average molecular weight of 4000-8000.

[0013] In a second aspect, a method for preparing the additive as described in the first aspect is provided, comprising the steps of: Polyepoxychloropropane and a tertiary amine compound are dissolved in a solvent and reacted at 50-200°C for 1-10 hours to obtain the additive. The solvent is selected from one or more of methanol, ethanol, ethylene glycol, acetonitrile, and N,N-dimethylformamide.

[0014] Thirdly, an electroplating solution for co-depositing tin-bismuth alloys is provided, comprising: the additives described in the first aspect.

[0015] In a preferred embodiment, the electroplating solution is prepared with water and further includes: tin salt, bismuth salt, boric acid, tin complexing agent, and bismuth complexing agent.

[0016] In a preferred embodiment, the concentration of the additive is 5~200ppm, the concentration of the tin salt is 0.1~0.6mol / L, the concentration of the bismuth salt is 0.1~0.6mol / L, the concentration of the boric acid is 0.5~1.5mmol / L, the concentration of the tin ligand is 0.1~0.5mol / L, and the concentration of the bismuth ligand is 0.1~0.3mol / L.

[0017] In a preferred embodiment, the tin salt is selected from one or more of stannous sulfate, tin methanesulfonate, and tin aminosulfonate, but is not limited thereto.

[0018] In a preferred embodiment, the bismuth salt is selected from one or more of bismuth nitrate, bismuth chloride, and bismuth sulfide, but is not limited thereto.

[0019] In a preferred embodiment, the tin ligand is selected from one or more of ethylenediaminetetraacetic acid, citric acid, and sodium gluconate, but is not limited thereto.

[0020] In a preferred embodiment, the bismuth ligand is selected from one or more of ethylenediaminetetraacetic acid, ammonium chloride, and iminodiacetic acid, but is not limited thereto.

[0021] The preferred technical solution, the method for preparing the electroplating solution, includes the following steps: The electroplating solution is obtained by dissolving tin salt, bismuth salt, boric acid, tin ligand, bismuth ligand and additives in water.

[0022] Fourthly, the application of an additive as described in the first aspect or an electroplating solution as described in the third aspect in the electroplating of tin-bismuth alloys is provided.

[0023] Fifthly, a method for preparing a tin-bismuth alloy coating is provided, comprising the following steps: Using an insoluble electrode as the anode and a metal substrate as the cathode, the anode and cathode are placed in the electroplating solution as described in the third aspect for electroplating treatment, thereby forming a tin-bismuth alloy coating on the metal substrate. The electroplating conditions include: maintaining the electroplating solution in a flowing state, controlling the temperature of the electroplating solution at 5~50℃, and the current density at 10~90mA / cm². 2 The electroplating time is 20~600min.

[0024] Sixthly, a method for preparing tin-bismuth alloy solder joints is provided, comprising the following steps: A tin-bismuth alloy coating was prepared using the preparation method described in the fifth aspect; Flux is applied to the tin-bismuth alloy plating, and the flux is removed after reflow treatment to obtain tin-bismuth alloy solder joints.

[0025] Beneficial effects: This invention provides an additive for co-depositing tin-bismuth alloys, its preparation method, and its application. Compared with existing technologies, its advantages include: (1) A novel additive for co-depositing tin-bismuth alloys is provided. This additive can form a dense protective film on the surface of electroplated metal by means of its unique molecular structure characteristics. By inhibiting the electron reduction process of hydrogen ions, it can effectively solve the common hydrogen evolution problem in the electroplating process and improve the coating quality and electroplating stability.

[0026] (2) A matching electroplating solution is provided, wherein the novel additives and complexing agents of the present invention are specially introduced into the electroplating solution. The two types of components can play a synergistic role in the electroplating process, significantly reducing Sn. 2+ and Bi 3+ The deposition potential difference allows for efficient co-deposition of the two metal ions, ensuring the compositional uniformity and performance stability of the tin-bismuth alloy coating.

[0027] (3) A matching method for preparing a tin-bismuth alloy coating is provided. By controlling the electroplating parameters, the performance of the coating and solder joint is ensured, thereby obtaining a Sn-Bi solder joint with uniform coating composition distribution and excellent performance. Attached Figure Description

[0028] Figure 1 This is a molecular schematic diagram of additives PQ-1, PQ-2, and PQ-3.

[0029] Figure 2 The diagram shows the structural characterization results of additive PQ-1; where (a) is the 1H NMR spectrum and (b) is the infrared spectrum.

[0030] Figure 3 The diagram shows the structural characterization results of additive PQ-2; where (a) is the 1H NMR spectrum and (b) is the infrared spectrum.

[0031] Figure 4 The diagram shows the structural characterization results of additive PQ-3; where (a) is the 1H NMR spectrum and (b) is the infrared spectrum.

[0032] Figure 5 These are comparison images of Sn-Bi solder joints before and after reflow in Application Example 1; where (a) is the SEM result before reflow, (b) is the SEM result after reflow, (a') is the result observed under a microscope before reflow, and (b') is the result observed under a microscope after reflow.

[0033] Figure 6 This is a process flow diagram for preparing Sn-Bi solder joints in Application Example 1.

[0034] Figure 7 This is a schematic diagram of the welding of the power module in Application Example 1.

[0035] Figure 8 These are coating microstructure distribution diagrams for Application Example 1-2 and Comparative Application Example 1-4.

[0036] Figure 9 These are coating microstructure distribution diagrams for Application Example 2, Comparative Application Example 2, and Comparative Application Examples 5-8. Detailed Implementation

[0037] This invention provides an additive for co-depositing tin-bismuth alloys, its preparation method, and its application. To make the objectives, technical solutions, and effects of this invention clearer and more explicit, the invention is further described in detail below.

[0038] Flip-chip solder joint packaging technology has become the mainstream interconnect solution due to its compact structure, high heat dissipation efficiency, and reliability advantages provided by local array interconnects. Currently, the main processes for solder joint preparation include metal mask evaporation, stencil printing, and electroplating. Among these, electroplating technology shows significant advantages in keeping with the trend of device miniaturization: this method is compatible with photolithography and can achieve fine customization of pitch and size at 100μm and below. With the continuous increase in integration density, the melting point characteristics of lead-free solder are particularly crucial. Sn-Bi solder has attracted much attention due to its excellent adhesion performance, cost-effectiveness, and ability to suppress PCB deformation. In particular, Sn-Bi solder with eutectic composition not only has a low melting point (138℃) but also a low coefficient of thermal expansion (15ppm / ℃), making it very suitable for high-density packaging scenarios. Given the unique properties of Sn-Bi solder and its good compatibility with electroplating processes, research on this system in electroplating preparation is receiving increasing attention. However, due to the significant potential difference between Sn and Bi, and the inconsistent growth rates of the two during the deposition process, achieving uniform and reliable Sn-Bi electroplated solder joints remains a challenging task.

[0039] In the electroplating process of Sn-Bi alloys, the hydrogen evolution effect is a key issue restricting the coating quality. Because Sn-Bi electroplating often uses acidic electrolyte systems such as sulfuric acid or methanesulfonic acid, the system contains a high concentration of hydrogen ions (H₂O). + It is easy to react with Sn on the cathode surface. 2+ Bi 3+ Competitive reduction—especially when the cathode current density increases or the electrolyte pH fluctuates, H + It is easier to obtain electrons to generate hydrogen gas. As the electroplating process progresses, a large number of hydrogen bubbles adhere to, accumulate, and escape from the cathode surface. On the one hand, this physically blocks the active sites of the cathode, leading to Sn... 2+ Bi 3+ Uniform adsorption is impossible; on the other hand, the airflow generated when bubbles escape will violently disturb the interfacial ion mass transfer, breaking the balance of orderly diffusion of metal ions, and finally forming a loose black powdery coating. This loose structure not only significantly reduces the conductivity and corrosion resistance of the coating, but also causes compositional runaway: the reduction rates of Sn and Bi in different regions can vary by more than 30%, and the coating composition deviates from the target eutectic ratio (such as Sn58Bi42). The Bi content in some regions may be as low as 40%, while in others it may soar to 70%, which completely fails to meet the requirements for coating composition uniformity in precision applications such as electronic packaging.

[0040] The present invention effectively solves the aforementioned problems by adding organic amines, heterocyclic compounds, and other additives to the electrolyte. The polar groups such as amino and hydroxyl groups in the additive molecules preferentially adsorb onto the highly active hydrogen evolution sites on the cathode surface, forming a dense protective film and inhibiting hydrogen evolution at its source. + The reduction reaction reduces the hydrogen evolution rate to less than one-fifth of its original level. Simultaneously, this adsorption membrane can also guide the hydrogen evolution process through steric hindrance. 2+ Bi 3+ Uniform diffusion along the cathode surface reduces the difference in ion reduction rates between different regions, thereby strictly controlling the compositional deviation of Sn and Bi in the coating within ±2%. Furthermore, with the reduction of hydrogen evolution, the porosity of the alloy layer can be reduced to below 5%, forming a dense and continuous microstructure. On the other hand, by designing and synthesizing additives with specific structures, it is possible to complex them with the already-complexed Sn. 2+ Bi 3+ Synergistic effect enables the control of the composition of the electroplated alloy layer; under the influence of additive concentration, the Bi content in the alloy layer can be controllably adjusted.

[0041] In addition to the advantages mentioned above, the most important benefit is the effective control of costs associated with electroplating Sn-Bi solder joints. By selecting the appropriate components of the electroplating solution and controlling the electroplating process, the costs incurred during electroplating are reduced. Furthermore, the electroplating solution uses environmentally friendly compounds, ensuring a low-toxicity and low-pollution preparation process.

[0042] Specifically, this invention provides an additive for co-depositing tin-bismuth alloys, wherein the additive is a polyether quaternary ammonium salt formed by the reaction of polyepoxychloropropane and a tertiary amine compound; The tertiary amine compound is selected from one or more of 3-dimethylamino-1-propanol, N,N-dimethylbutylamine, and 1-methylimidazole.

[0043] In some embodiments, the additive is selected from one of the following structures: ; Where n and p are independently selected from natural numbers from 0 to 45; The sum of n and p is 20 to 100, preferably 40 to 80, and more preferably 50 to 70.

[0044] In some embodiments, the molar ratio of the polyepoxychloropropane to the tertiary amine compound is 1:(0.05~5), preferably 1:(0.1~2), and more preferably 1:(0.3~0.8).

[0045] In some embodiments, the polyepoxychloropropane has a weight-average molecular weight (Mw) of 4,000 to 8,000, preferably 5,000 to 7,000, and more preferably 6,000.

[0046] Based on the same inventive concept, embodiments of the present invention provide a method for preparing the additive as described above, comprising the following steps: Polyepoxychloropropane and a tertiary amine compound are dissolved in a solvent and reacted at 50-200°C for 1-10 hours to obtain the additive. The solvent is selected from one or more of methanol, ethanol, ethylene glycol, acetonitrile, and N,N-dimethylformamide.

[0047] In some embodiments, the method for preparing the polyepoxychloropropane includes the steps of: The Lewis acid catalyst and the initiator were dissolved in an organic solvent to obtain the first mixture; Epichlorohydrin was dissolved in an organic solvent to obtain a second mixture; The second mixture is added dropwise to the first mixture, and after being mixed evenly, it is reacted under an inert atmosphere at 0~5℃ for 0.5~2h to obtain the polyepoxychloropropane.

[0048] In some more specific embodiments, in the method for preparing polyepoxychloropropane, the Lewis acid catalyst is boron trifluoride diethyl ether, the initiator is ethylene glycol, and the organic solvent is dichloroethane.

[0049] In some more specific embodiments, in the method for preparing polyepoxychloropropane, the molar ratio of the Lewis acid catalyst, initiator and epichlorohydrin is (0.01~0.1):(0.4~0.8):1.

[0050] In some embodiments, the method for preparing the additive specifically includes the following steps: Polyepoxychloropropane and solvent are mixed, and heated to 50°C while stirring. The polyepoxychloropropane is uniformly dispersed in the solvent to obtain a mixed solution. A tertiary amine compound is added to the mixed solution, and the mixture is reacted at 50-200°C for 1-10 hours to obtain the additive.

[0051] In some more specific embodiments, in the preparation method of the additive, the amount of polyepoxychloropropane is 0.01~0.1 mol, the amount of the tertiary amine compound is 0.005~0.05 mol, and the amount of solvent is 10~50 mL.

[0052] Based on the same inventive concept, embodiments of the present invention provide an electroplating solution for co-depositing tin-bismuth alloys, comprising: the additives described above.

[0053] In some embodiments, the electroplating solution is prepared with water and further includes tin salts, bismuth salts, boric acid, tin ligands, and bismuth ligands.

[0054] In some embodiments, the concentration of the additive is 5-200 ppm (1 ppm = 1 mg / L), the concentration of the tin salt is 0.1-0.6 mol / L, the concentration of the bismuth salt is 0.1-0.6 mol / L, the concentration of the boric acid is 0.5-1.5 mmol / L, the concentration of the tin ligand is 0.1-0.5 mol / L, and the concentration of the bismuth ligand is 0.1-0.3 mol / L.

[0055] In some embodiments, the tin salt is selected from one or more of stannous sulfate, tin methanesulfonate, and tin aminosulfonate, but is not limited thereto.

[0056] In some embodiments, the bismuth salt is selected from one or more of bismuth nitrate, bismuth chloride, and bismuth sulfide, but is not limited thereto.

[0057] In some embodiments, the tin ligand is selected from one or more of ethylenediaminetetraacetic acid, citric acid, and sodium gluconate, but is not limited thereto.

[0058] In some embodiments, the bismuth ligand is selected from one or more of ethylenediaminetetraacetic acid, ammonium chloride, and iminodiacetic acid, but is not limited thereto.

[0059] In some embodiments, the method for preparing the electroplating solution includes the steps of: The electroplating solution is obtained by dissolving tin salt, bismuth salt, boric acid, tin ligand, bismuth ligand and additives in water.

[0060] In some embodiments, the method for preparing the electroplating solution, after the step of dissolving tin salt, bismuth salt, boric acid, tin ligand, bismuth ligand and additives in water, further includes the step of adjusting the pH to 1-2.

[0061] In some more specific embodiments, the method for preparing the electroplating solution includes the following steps: Boric acid, tin salt, and tin complexing agent are dissolved in water to obtain the first solution; The bismuth salt was dissolved in water to obtain a second solution; The first and second solutions are mixed, and bismuth ligands and additives are added. The mixture is stirred until all components are completely dissolved, ensuring that the solution is transparent and free of emulsification and precipitates. The pH is then adjusted to 1-2 to obtain the electroplating solution.

[0062] In some more specific embodiments, the electroplating solution is prepared and used immediately to avoid oxidation due to prolonged exposure of the solution, which would affect the subsequent electroplating effect.

[0063] Based on the same inventive concept, embodiments of the present invention provide the application of the additives described above or the electroplating solutions described above in the electroplating of tin-bismuth alloys.

[0064] Based on the same inventive concept, embodiments of the present invention provide a method for preparing a tin-bismuth alloy coating, comprising the following steps: Using an insoluble electrode as the anode and a metal substrate as the cathode, the anode and cathode are placed in the electroplating solution described above for electroplating treatment, thereby forming a tin-bismuth alloy coating on the metal substrate. The electroplating conditions include: maintaining the electroplating solution in a flowing state, controlling the temperature of the electroplating solution at 5~50℃, and the current density at 10~90mA / cm². 2 The electroplating time is 20~600min.

[0065] In some embodiments, the electroplating process specifically includes the steps of placing the anode and cathode at opposite ends of the electroplating tank and connecting them to the positive and negative terminals of a DC power supply.

[0066] In some embodiments, the material of the insoluble electrode is selected from one or more of carbon, platinum, and graphite.

[0067] In some embodiments, the metal substrate is made of copper.

[0068] In some embodiments, the method of keeping the electroplating solution in a flowing state is selected from one or more of magnetic stirring, mechanical stirring, bubbling and blowing, and ultrasound.

[0069] Based on the same inventive concept, embodiments of the present invention provide a method for preparing tin-bismuth alloy solder joints, including the following steps: A tin-bismuth alloy coating was prepared using the preparation method described above. Flux is applied to the tin-bismuth alloy plating, and the flux is removed after reflow treatment to obtain tin-bismuth alloy solder joints.

[0070] In some embodiments, the flux is selected from rosin or water-soluble resins (such as polyvinyl alcohol).

[0071] In some implementations, the reflux process specifically includes: First stage: carried out under an inert atmosphere, heated to 80~100℃, and held for 20~40 seconds; Second stage: Carry out under an inert atmosphere, heat to 180~220℃, and hold for 3~7 minutes; Phase 3: Switch to air cooling mode.

[0072] In some embodiments, the removal of the flux is performed after cooling, using an alcohol wipe. The present invention will be further described below through specific embodiments.

[0073] Example 1 This embodiment provides an additive PQ for co-depositing tin-bismuth alloys, as detailed below: (1) Synthesis of PECH: Clean and dry the glassware and assemble the experimental equipment, connecting the gas and water pipes.

[0074] Add 0.03 mol boron trifluoride diethyl ether (Lewis acid catalyst), 0.45 mol ethylene glycol (initiator), and 60 mL dichloroethane (solvent) to a three-necked flask to obtain a mixture; add a mixture of 0.75 mol epichlorohydrin and 60 mL dichloroethane to a constant pressure funnel.

[0075] The mixture was vigorously stirred under nitrogen atmosphere for 20-30 minutes to expel air and water vapor, so that the Lewis acid catalyst and initiator were uniformly dispersed in the solvent and the solution temperature was lowered.

[0076] Slowly add the mixture of epichlorohydrin and dichloroethane dropwise over approximately 40 minutes, starting the timer after the addition is complete. Use an ice-salt bath to prevent the temperature from rising, maintaining the reaction temperature at 0–5°C.

[0077] After reacting for 1 hour, the reaction solution was poured into a beaker, and an equal volume of ammonia was added to quench the reaction and stop it. The mixture was washed with pure water until the pH was neutral, and then separated to obtain a PECH solution.

[0078] The solvent and impurities were removed by rotary evaporation at 80°C to obtain the final product PECH. The Mw of PECH was determined to be around 6000.

[0079] (2) Synthesis of additive PQ-1: Clean and dry the glassware and assemble the experimental equipment, and connect the water pipes.

[0080] Add 0.05 mol of PECH and 30 mL of ethylene glycol to a three-necked flask, heat to 50 °C with stirring to ensure that PECH is uniformly dispersed in ethylene glycol; add 0.025 mol of 1-methylimidazole and react at 170 °C for 2 h.

[0081] After the reaction, the mixture was cooled to room temperature for purification. Because quaternary ammonium salts are highly polar, the reaction solution was mixed with 30 mL of acetone and then added dropwise to ethyl acetate to precipitate the crude product. The crude product was centrifuged to allow it to settle, and excess ethyl acetate was added. The mixture was shaken and centrifuged again to collect the crude product. This process was repeated until the product was completely insoluble after adding ethyl acetate and shaking, at which point the pure product was obtained. The pure product was dried in a vacuum oven at 70°C for 12 hours to obtain the additive, designated PQ-1. A molecular diagram of PQ-1 is shown below. Figure 1 As shown in (a), the NMR characterization results are as follows: Figure 2 As shown in (a), the infrared characterization results are as follows: Figure 2 As shown in (b).

[0082] Example 2 This embodiment provides an additive PQ-2 for co-depositing tin-bismuth alloys, as detailed below: (1) Synthesis of PECH: The synthesis steps for PECH are the same as in Example 1.

[0083] (2) Synthesis of additive PQ-2: Clean and dry the glassware and assemble the experimental equipment, and connect the water pipes.

[0084] Add 0.03 mol of PECH and 25 mL of ethanol to a three-necked flask, heat to 50 °C with stirring to uniformly disperse PECH in the ethanol; add 0.015 mol of 3-dimethylamino-1-propanol, and react at 100 °C for 5 h.

[0085] After the reaction, the mixture was cooled to room temperature for purification. Because quaternary ammonium salts are highly polar, the reaction solution was mixed with 30 mL of acetone and then added dropwise to ethyl acetate to precipitate the crude product. The crude product was centrifuged to allow it to settle, and excess ethyl acetate was added. The mixture was shaken and centrifuged again to collect the crude product. This process was repeated until the product was completely insoluble after adding ethyl acetate and shaking, at which point the pure product was obtained. The pure product was dried in a vacuum oven at 70°C for 12 hours to obtain the additive, designated PQ-2. A molecular diagram of PQ-2 is shown below. Figure 1 As shown in (b), the NMR characterization results are as follows: Figure 3 As shown in (a), the infrared characterization results are as follows: Figure 3 As shown in (b).

[0086] Example 3 This embodiment provides an additive PQ-3 for co-depositing tin-bismuth alloys, as detailed below: (1) Synthesis of PECH: The synthesis steps for PECH are the same as in Example 1.

[0087] (2) Synthesis of additive PQ-3: Clean and dry the glassware and assemble the experimental equipment, and connect the water pipes.

[0088] Add 0.04 mol of PECH and 25 mL of methanol to a three-necked flask, heat to 50 °C with stirring to ensure that PECH is uniformly dispersed in methanol; then add 0.02 mol of N,N-dimethylbutylamine and react at 70 °C for 8 h.

[0089] After the reaction, the mixture was cooled to room temperature for purification. Because quaternary ammonium salts are highly polar, the reaction solution was mixed with 30 mL of acetone and then added dropwise to ethyl acetate to precipitate the crude product. The crude product was centrifuged to allow it to settle, and excess ethyl acetate was added. The mixture was shaken and centrifuged again to collect the crude product. This process was repeated until the product was completely insoluble after adding ethyl acetate and shaking, at which point the pure product was obtained. The pure product was dried in a vacuum oven at 70°C for 12 hours to obtain the additive, designated PQ-3. A molecular diagram of PQ-2 is shown below. Figure 1 As shown in (c), the NMR characterization results are as follows: Figure 4 As shown in (a), the infrared characterization results are as follows: Figure 4 As shown in (b).

[0090] Example 4 This embodiment provides an electroplating solution for co-depositing tin-bismuth alloys, as detailed below: The electroplating solution consists of: 0.15 mol / L stannous sulfate, 0.025 mol / L bismuth nitrate, 0.65 mol / L boric acid, 0.11 mol / L citric acid, 0.165 mol / L ethylenediaminetetraacetic acid, 100 ppm of additive PQ prepared in Example 1, and the remainder being pure water.

[0091] The preparation steps specifically include: S1. Add boric acid to 400 mL of pure water and stir at 150 rpm for 30 min at room temperature until the solution is completely dissolved. Let it stand and cool to obtain solution A. S2. Add citric acid to solution A obtained in step S1, stir at 300 rpm for 30 minutes at room temperature until the solution is completely dissolved, let stand and cool to obtain solution B; S3. Add stannous sulfate to the B solution obtained in step S2, stir at 300 rpm for 10 minutes at room temperature until the solution is completely dissolved, let stand and cool to obtain the C solution; S4. Add bismuth nitrate to 10 mL of dilute nitric acid and stir at 150 rpm for 30 min at room temperature until the solution is completely dissolved. Let it stand and cool to obtain solution D. S5. Add the solution D obtained in step S4 to the solution C obtained in step S3 and mix. Then add ethylenediaminetetraacetic acid and stir at 300 rpm for 10 minutes at room temperature until the solution is completely dissolved. Let it stand and cool to obtain solution E. S6. Add the additive PQ-1 prepared in Example 1 to the E solution obtained in step S5, add deionized water to make up to 500 mL, and stir at 500 rpm for 30 min at room temperature until the mixture is homogeneous to obtain the electroplating solution.

[0092] Example 5 This embodiment provides an electroplating solution for co-depositing tin-bismuth alloys. The only difference from Example 4 is that the concentration of additive PQ-1 prepared in Example 1 is changed to 400 ppm in the electroplating solution components, while the other components and preparation steps are the same as in Example 4.

[0093] Comparative Example 1 This comparative example provides an electroplating solution for co-depositing tin-bismuth alloys. The only difference from Example 4 is that the additive PQ-1 prepared in Example 1 is not added to the electroplating solution components. The remaining components and preparation steps are the same as in Example 4.

[0094] Comparative Example 2 This comparative example provides an electroplating solution for co-depositing tin-bismuth alloys. The only difference from Example 5 is that the additive PQ-1 prepared in Example 1 is replaced with the same concentration of commercial additive myrcene ether (POELE). The remaining components and preparation steps are the same as in Example 5.

[0095] Application Example 1 This application example provides a method for preparing Sn-Bi solder joints using the electroplating solution of Example 4 and applying it to power module soldering. The specific steps are as follows: S1. Preparation of the electroplating substrate. The substrate can be a component in a power semiconductor that requires solder joints, such as a patterned wafer with photoresist, specifically an electroplated wafer (copper substrate). The substrate is sequentially subjected to acid pickling and deionized water cleaning. The acid pickling process involves immersion and agitation in a 5-10% (w / v) sulfuric acid (H2SO4) solution or immersion in ultrasonication. Finally, it is rinsed with deionized water.

[0096] S2. Electroplating. Using plate-shaped carbon as the anode and a copper substrate as the cathode, the electroplating solution from Example 4 was added to the electroplating tank. The anode and cathode were placed at opposite ends of the tank, respectively, and immersed in the electroplating solution, connected to the positive and negative terminals of a DC power supply. Magnetic stirring was used to control the flow rate of the electroplating solution at 400 rpm, the solution temperature at 25°C, and the current density at 10 mA / cm². 2 The electroplating time was 30 minutes. After electroplating, a Sn-Bi alloy layer was formed on the copper substrate.

[0097] S3. Preparation before reflow soldering. First, treat the surface of the copper substrate to remove any residual adhesive substances in the control pattern area. After the surface reaches the required cleanliness, dry it and then apply flux before proceeding. The process for removing residual adhesive substances in the control pattern area is an alkaline chemical degumming method, using a 10g / L NaOH solution as the degumming solution and rosin as the flux.

[0098] S4. Reflow to form solder joints and remove flux. Place the copper substrate containing the Sn-Bi alloy layer (coated but not reflowed) into the reflow oven at a pressure of 20 MPa. Reflow parameters are set as follows: first stage temperature 90℃, holding time 30s; second stage temperature 200℃, holding time 5min; third stage air cooling. Finally, remove the copper substrate containing the Sn-Bi solder joints and remove the flux using alcohol to obtain qualified Sn-Bi solder joints.

[0099] The obtained Sn-Bi solder joints before and after reflow are as follows Figure 5 As shown. Figure 5 In the figure, (a) and (b) are SEM results, and (a') and (b') are results observed by microscopy. It can be clearly seen that the Bi element in the Sn-Bi alloy layer exhibits a uniform distribution.

[0100] The process flow for preparing Sn-Bi solder joints is as follows: Figure 6 As shown in the diagram. A schematic diagram of applying Sn-Bi solder joints to power module soldering is shown below. Figure 7 As shown. The coating structure distribution of the Sn-Bi solder joint is as follows. Figure 8 As shown in (b).

[0101] Comparative Application Example 1 This comparative application example provides a method for preparing Sn-Bi solder joints using the electroplating solution of Example 4 and applying it to power module soldering. The only difference from Application Example 1 is that the current density in step S2 of the electroplating process is different; the current density in this comparative application example is 20 mA / cm². 2 The remaining steps are the same as in Application Example 1. The coating structure distribution of the Sn-Bi solder joint is as follows: Figure 8 As shown in (e).

[0102] Application Example 2 This application example provides a method for preparing Sn-Bi solder joints for power module soldering using the electroplating solution of Example 5. The only difference from Application Example 1 is the concentration of additive PQ-1 in the electroplating solution. In this application example, the concentration of additive PQ-1 is 400 ppm. The remaining steps are the same as in Application Example 1. The plating structure distribution of the Sn-Bi solder joint is as follows: Figure 8 (c) or Figure 9 As shown in (a).

[0103] Comparative Application Example 2 This comparative application example provides a method for preparing Sn-Bi solder joints using the electroplating solution of Example 5 and applying it to power module soldering. The only difference from Application Example 2 is that the current density in step S2 of the electroplating process is different; the current density in this comparative application example is 20 mA / cm². 2 The remaining steps are the same as in Application Example 2. The coating structure distribution of the Sn-Bi solder joint is as follows: Figure 8 (f) or Figure 9 As shown in (b).

[0104] Comparative Application Example 3 This comparative application example provides a method for preparing Sn-Bi solder joints for power module soldering using the electroplating solution of Comparative Example 1. The only difference from Application Example 1 is the composition of the electroplating solution; additive PQ-1 is not added in this comparative application example. The remaining steps are the same as in Application Example 1. The plating structure distribution of the Sn-Bi solder joint is as follows: Figure 8 As shown in (a).

[0105] Comparative Application Example 4 This comparative application example provides a method for preparing Sn-Bi solder joints for power module soldering using the electroplating solution of Comparative Example 1. The only difference from Application Example 2 is the composition of the electroplating solution; additive PQ-1 is not added in this comparative application example. The remaining steps are the same as in Application Example 2. The plating structure distribution of the Sn-Bi solder joint is as follows: Figure 8 As shown in (d).

[0106] Comparative Application Example 5 This comparative application example provides a method for preparing Sn-Bi solder joints using the electroplating solution of Example 5 and applying it to power module soldering. The only difference from Application Example 2 is that the current density in step S2 of the electroplating process is different; the current density in this comparative application example is 50 mA / cm². 2 The remaining steps are the same as in Application Example 2. The coating structure distribution of the Sn-Bi solder joint is as follows: Figure 9 As shown in (c).

[0107] Comparative Application Example 6 This comparative application example provides a method for preparing Sn-Bi solder joints using the electroplating solution of Comparative Example 2 and applying it to power module soldering. The only difference from Application Example 2 is the composition of the electroplating solution; in this comparative application example, the additive POELE is added. The remaining steps are the same as in Application Example 2. The plating structure distribution of the Sn-Bi solder joint is as follows: Figure 9 As shown in (d).

[0108] Comparative Application Example 7 This comparative application example provides a method for preparing Sn-Bi solder joints using the electroplating solution of Comparative Example 2 and applying it to power module soldering. The only difference from Comparative Example 2 is the composition of the electroplating solution; in this comparative application example, the additive POELE is added. The remaining steps are the same as in Comparative Example 2. The plating structure distribution of the Sn-Bi solder joint is as follows: Figure 9 As shown in (e).

[0109] Comparative Application Example 8 This comparative application example provides a method for preparing Sn-Bi solder joints using the electroplating solution of Comparative Example 2 and applying it to power module soldering. The only difference from Comparative Example 5 is the composition of the electroplating solution; in this comparative application example, the additive POELE is added. The remaining steps are the same as in Comparative Example 5. The plating structure distribution of the Sn-Bi solder joint is as follows: Figure 9 As shown in (f).

[0110] Performance testing The Sn-Bi solder joints prepared according to Case 1-2 and Comparative Application Example 1-2 were tested, and the specific judgment criteria and results are as follows: Appearance: Visual inspection and microscopic examination are used to determine whether the coating is fine, continuous, dense and uniform.

[0111] Microscopic crystal phase: The crystal phase image is taken using a scanning electron microscope at 2000x magnification. If the crystal phase is clear, the crystals are fine, and there are no voids, it is considered qualified.

[0112] Bi content: The tin-bismuth content is tested using a scanning electron microscope. A bismuth content of 30-40% (w / w) is considered acceptable.

[0113] Table 1. Crystal phase diagram and elemental analysis results of Sn-Bi solder joints

[0114] The above results show that the Sn-Bi coatings of Application Examples 1 and 2 have uniform composition distribution and excellent performance, meeting the requirements for Sn-Bi solder joint preparation. In contrast, the Sn-Bi coatings of Comparative Application Examples 1 and 2 have obvious defects: the Bi content does not meet the standard, and the particle size is too small, resulting in solder joints that do not meet the appearance requirements after reflow soldering. This comparative result further proves that the synergistic effect of the electroplating solution ratio and electroplating parameters in this invention is the key to ensuring the performance of the coating and solder joints.

[0115] The specific coating microstructure distribution of Application Example 1-2 and Comparative Application Example 1-8 is as follows: Figure 8 and Figure 9 As shown. By Figure 8 It can be seen that as the current density increases, the proportion of Bi in the coating decreases; however, when the concentration of additive PQ-1 in the solution increases, the Bi content increases in the opposite direction. This indicates that within a fixed current density range, additive PQ-1 can effectively interfere with the electroplating behavior of Bi, providing a feasible way to individually control the Bi content in the coating. Figure 9 It is known that changing the current density during the electroplating process and using the commercial additive POELE caused a compositional imbalance, resulting in a rapid decrease in the Bi content in the microstructure.

[0116] It should be understood that the application of the present invention is not limited to the examples above. Those skilled in the art can make improvements or modifications based on the above description, and all such improvements and modifications should fall within the protection scope of the appended claims.

Claims

1. An additive for co-depositing a tin bismuth alloy, characterized in that, The additive is a polyether quaternary ammonium salt formed by reaction of polyepichlorohydrin and a tertiary amine compound; The tertiary amine compound is selected from one or more of 3-dimethylamino-1-propanol, N,N-dimethylbutylamine and 1-methylimidazole.

2. The additive of claim 1, wherein The additive is selected from one of the following structures: ； n and p are independently selected from natural numbers of 0-45, and the sum of n and p is 20-100.

3. The additive of claim 1, wherein The molar ratio of the polyepichlorohydrin and the tertiary amine compound is 1:(0.05-5); The weight average molecular weight of the polyepichlorohydrin is 4000-8000.

4. A process for the preparation of an additive as claimed in any one of claims 1 to 3, characterized in that, The method comprises the steps of: The polyepichlorohydrin and the tertiary amine compound are dissolved in a solvent and reacted at 50-200°C for 1-10 hours to obtain the additive; The solvent is selected from one or more of methanol, ethanol, ethylene glycol, acetonitrile and N,N-dimethylformamide.

5. An electroplating solution for co-deposition of tin bismuth alloy, characterized in that, The method comprises the steps of: The additive is as claimed in any one of claims 1-2.

6. The electroplating solution of claim 5, wherein, The electroplating solution is prepared with water and further comprises a tin salt, a bismuth salt, boric acid, a tin complexing agent and a bismuth complexing agent.

7. The electroplating solution of claim 6, wherein The concentration of the additive is 5-200 ppm, the concentration of the tin salt is 0.1-0.6 mol / L, the concentration of the bismuth salt is 0.1-0.6 mol / L, the concentration of the boric acid is 0.5-1.5 mmol / L, the concentration of the tin complexing agent is 0.1-0.5 mol / L, and the concentration of the bismuth complexing agent is 0.1-0.3 mol / L. The tin salt is selected from one or more of stannous sulfate, tin methyl sulfonate and tin sulfamic acid; The bismuth salt is selected from one or more of bismuth nitrate, bismuth chloride and bismuth sulfide; The tin complexing agent is selected from one or more of ethylenediaminetetraacetic acid, citric acid and sodium gluconate; The bismuth complexing agent is selected from one or more of ethylenediaminetetraacetic acid, ammonium chloride and iminodiacetic acid.

8. Use of the additive as claimed in any one of claims 1-3 or the electroplating solution as claimed in any one of claims 5-7 in electroplating of tin-bismuth alloy.

9. A method for producing a tin-bismuth alloy plating layer, characterized by, The method comprises the steps of: An insoluble electrode is used as an anode, a metal substrate is used as a cathode, the anode and the cathode are placed in the electroplating solution as claimed in any one of claims 5-7 to perform electroplating treatment, and a tin-bismuth alloy plating layer is formed on the metal substrate; The conditions of the electroplating treatment include: keeping the electroplating solution in a flowing state, controlling the temperature of the electroplating solution at 5-50 ℃, the current density at 10-90 mA / cm 2 , and the electroplating time at 20-600 min.

10. A method of producing a solder joint of a tin bismuth alloy, characterized by, The method comprises the steps of: The tin-bismuth alloy plating layer is prepared by using the preparation method as claimed in claim 9; The tin-bismuth alloy plating layer is coated with a soldering flux, the soldering flux is removed after reflow treatment, and a tin-bismuth alloy solder joint is obtained.

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