Cyanide-free Au-Sn electroplating solution and application

Abstract

The invention discloses a cyanide-free Au-Sn electroplating solution and application, and belongs to the technical field of electroplating, the electroplating solution is composed of a gold source, a tin source, a gold complexing agent, a tin complexing agent, an additive and a pH buffering agent; the gold source is gold mercaptosulfonate; the tin complexing agent is mercaptoacetic acid and salt thereof; and the pH value of the cyanide-free Au-Sn electroplating solution is 3 to 11. The electroplating liquid provided by the invention does not contain extremely toxic substances, has relatively high storage stability and electroplating stability, and still keeps a clear and transparent state even under high and low temperature change, illumination, long-time storage or long-time electroplating, and an Au-Sn alloy plated part with uniform and stable components and high reproducibility is obtained in long-time storage or long-time electroplating; therefore, the performance of an Au-Sn alloy plating piece obtained through electroplating is effectively guaranteed, the performance of the electroplating solution is excellent, and application to the packaging technology of microelectronic or optoelectronic devices is facilitated.

Description

Technical Field

[0001] The present invention relates to the technical field of electroplating, and more specifically to a cyanide-free Au-Sn electroplating solution and application thereof. Background Art

[0002] Au-Sn eutectic alloy solder (Au-30.0at.%Sn) has the advantages of high thermal conductivity, high electrical conductivity, high elongation and good wetting performance. It can realize flux-free welding and is widely used in the packaging technology of microelectronics and optoelectronic devices, such as achieving MEMS wafer-level airtight packaging and high-power LED high heat dissipation packaging.

[0003] The traditional Au-Sn electroplating process usually uses a cyanide system. Although it has the advantages of high storage stability, long service life, high electroplating stability, and excellent performance of Au-Sn alloy plated parts, cyanide is a highly toxic substance and does not meet the requirements of green electroplating and sustainable development. Therefore, the non-toxic and pollution-free cyanide-free Au-Sn electroplating system is gradually replacing the cyanide Au-Sn electroplating system.

[0004] The main reasons for the instability of cyanide-free Au-Sn electroplating solution are the following three points: 1. Sn(Ⅱ) is easily oxidized to generate easily hydrolyzed Sn(Ⅳ) and form a precipitate; 2. Au(Ⅰ) is easily disproportionated to produce Au precipitate; 3. Au(Ⅰ) or Au(Ⅲ) and Sn(Ⅱ) are easy to spontaneously react to form Au precipitate. As a result, the currently used cyanide-free Au-Sn electroplating system still has the following two problems: 1. The storage stability of Au-Sn electroplating solution is low and the service life is short. The electroplating solution decomposes its components during storage and then forms a precipitate. Chinese patents with publication numbers CN107287629A and CN102644098A both disclose a sulfite system cyanide-free Au-Sn electroplating solution, but the sulfite ion has the problem of easy decomposition, causing the gold ion to lose its ligand, undergo a disproportionation reaction to form a gold precipitate, and cause the Au-Sn electroplating solution to fail. Second, the electroplating stability is low, the reproducibility of high-performance Au-Sn eutectic plated parts is poor, and the composition of the Au-Sn alloy plated parts obtained during long-term storage or long-term electroplating changes continuously. The US patent with publication number US2003134142A1 discloses a chloride-citric acid system cyanide-free Au-Sn electroplating solution, but after 3 days, a black precipitate containing gold, tin and oxygen elements is generated, resulting in a gradual decrease in the Sn content in the Au-Sn alloy plated parts within 3 days, causing the Au-Sn electroplating solution to fail. Summary of the invention

[0005] The purpose of the present invention is to overcome the above-mentioned defects of the prior art, provide a cyanide-free Au-Sn electroplating solution and its application, utilize mercaptosulfonic acid gold salt and specific tin complexing agent that do not contain highly toxic substances to improve the stability of gold ions and tin ions, thereby improving the storage stability and electroplating stability of the Au-Sn electroplating solution, obtain Au-Sn alloy plated parts with uniform and stable composition and high reproducibility during long-term storage or long-term electroplating, and at the same time, the mutual synergistic effect between the gold complexing agent, additives and pH buffering agent effectively improves the performance of the Au-Sn alloy plated parts.

[0006] To achieve the above object, the technical solution of the present invention is as follows: A cyanide-free Au-Sn electroplating solution comprises a gold source, a tin source, a gold complexing agent, a tin complexing agent, an additive and a pH buffer; the gold source is used in an amount such that the molar concentration of gold ions in the electroplating solution is 0.01 mol / L-0.04 mol / L; the tin source is used in an amount such that the molar concentration of tin ions in the electroplating solution is 0.02 mol / L-0.20 mol / L; the gold source is mercaptosulfonic acid gold salt; the tin complexing agent is thioglycolic acid and its salt; and the pH of the cyanide-free Au-Sn electroplating solution is 3-11.

[0007] The invention also discloses an application of the cyanide-free Au-Sn electroplating solution in preparing Au-Sn alloy plated parts.

[0008] The present invention also discloses an application of the cyanide-free Au-Sn electroplating solution as described above, or the Au-Sn alloy plated parts obtained by the application as described above in the packaging technology of microelectronic or optoelectronic devices.

[0009] Implementing the embodiments of the present invention will have the following beneficial effects: The mercaptosulfonic acid gold salt used in the cyanide-free Au-Sn electroplating solution provided by the present invention has high storage stability, the mercaptosulfonic acid salt can form a strong coordination bond with the gold ions, is not easily affected by environmental factors such as temperature, humidity, light and oxidation, does not have the problem of easy decomposition itself, ensures the stability of the gold ions, and then ensures the high storage stability of the cyanide-free Au-Sn electroplating solution. In addition, the mercaptosulfonic acid gold salt has high compatibility with the complexing agent and additive provided by the present invention, and can coexist with them to further improve the storage stability of the Au-Sn electroplating solution, thereby effectively ensuring the performance of the Au-Sn alloy plated parts obtained by electroplating. At the same time, the preparation method of the mercaptosulfonic acid gold salt is simple, the conversion rate is high, and it is stable and efficient.

[0010] The thioglycolic acid and its salt used in the cyanide-free Au-Sn electroplating solution provided by the present invention can stabilize tin ions and inhibit the oxidation of Sn(II) to Sn(IV), which not only inhibits the generation of tin-containing precipitation, but also keeps the deposition potential difference between Au and Sn in the cyanide-free Au-Sn electroplating solution stable during long-term storage or long-term electroplating, and obtains Au-Sn alloy plated parts with uniform and stable composition and high reproducibility.

[0011] The cyanide-free Au-Sn electroplating solution provided by the present invention does not contain highly toxic substances, has high storage stability, can be stably stored at room temperature for more than 6 months, and remains clear and transparent even under conditions of high and low temperature changes, light, long-term storage or long-term electroplating, without precipitation generation or discoloration.

[0012] The cyanide-free Au-Sn electroplating solution provided by the present invention has high electroplating stability. The Au-Sn electroplating solution after long-term storage or long-term electroplating has the same electroplating effect as the newly configured Au-Sn electroplating solution. The obtained Au-Sn alloy plated parts have uniform and stable components and high reproducibility, and problems such as component self-decomposition or Au-Sn electroplating solution failure do not occur.

[0013] The cyanide-free Au-Sn electroplating solution provided by the invention has excellent performance, good dispersibility and covering ability, high cathode current efficiency, and can obtain high-performance Au-Sn alloy plated parts within a wider pH and average current density range.

[0014] The composition of the Au-Sn alloy plated parts obtained by electroplating with the cyanide-free Au-Sn electroplating solution provided by the present invention includes but is not limited to the Au-30.0at.%Sn eutectic alloy composition, the plated part composition deviation is less than 1.0%, the Au-Sn alloy plated parts have stable composition after long-term electroplating, good bonding with the substrate, bright appearance, flatness and density, low porosity, and are conducive to the application in the packaging technology of microelectronics or optoelectronic devices. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 This is the linear sweep voltammetric curve of Au and Sn in the cyanide-free Au-Sn electroplating solution prepared in Example 1 of the present invention (the test potential is compared to the electrode potential of a saturated calomel electrode).

[0016] Figure 2 This is a composition change diagram of the Au-Sn alloy plated part prepared when the average current density is 4.0ASD during long-term electroplating in Example 3 of the present invention.

[0017] Figure 3 This is the linear sweep voltammetric curve of Au and Sn in the cyanide-free Au-Sn electroplating solution prepared in Comparative Example 1 of the present invention (the test potential is compared to the electrode potential of a saturated calomel electrode). DETAILED DESCRIPTION

[0018] The present invention is further described below in conjunction with specific embodiments, but the present invention is not limited in any way.

[0019] The invention discloses a cyanide-free Au-Sn electroplating solution. The electroplating solution consists of a gold source, a tin source, a gold complexing agent, a tin complexing agent, an additive and a pH buffer. The amount of the gold source is such that the molar concentration of gold ions in the electroplating solution is 0.01 mol / L-0.04 mol / L; the amount of the tin source is such that the molar concentration of tin ions in the electroplating solution is 0.02 mol / L-0.20 mol / L. The gold source is mercaptosulfonic acid gold salt; the tin complexing agent is thioglycolic acid and its salt; and the pH of the cyanide-free Au-Sn electroplating solution is 3-11.

[0020] In a specific embodiment, the molar concentration ratio of gold ions to tin ions in the electroplating solution is 1:(2-6). Specifically, if the molar concentration ratio is lower than 1:2, the Sn content is too low, and only Au5Sn phase alloy (Au-16.7at.%Sn) can be obtained by electroplating. If the molar concentration ratio is higher than 1:6, the Sn content is too high, and only AuSn phase alloy (Au-50.0at.%Sn) can be obtained by electroplating.

[0021] In a specific embodiment, the preparation method of mercaptosulfonate gold salt comprises the following steps: (1) Dissolving gold flakes with a gold content of more than 99.99% in aqua regia, and adding deionized water to the resulting syrupy solution to remove nitrogen oxides to obtain a chloroauric acid solution, and then adjusting the pH of the chloroauric acid solution to 6-7 to obtain a first reaction solution.

[0022] (2) Dissolving the mercaptosulfonate in deionized water and adjusting the pH of the solution to 9-13 to obtain a second reaction solution.

[0023] (3) The first reaction liquid and the second reaction liquid are mixed and reacted to obtain mercaptosulfonic acid gold salt.

[0024] In a specific embodiment, in step (1), the mass ratio of the gold flakes to the aqua regia is 1:(5-10).

[0025] In a specific embodiment, in step (2), the mercaptosulfonate includes at least one of 2-mercaptoethanesulfonate, 3-mercapto-1-propanesulfonate, 2,3-dimercaptopropanesulfonate, 4-mercapto-1-butanesulfonate, 3,4-dimercaptobutanesulfonate and 2,4-dimercaptobutanesulfonate.

[0026] In a specific embodiment, in step (3), the molar concentration ratio of the gold ions in the first reaction solution to the mercaptosulfonate in the second reaction solution is 1:(5-15). Specifically, if the molar concentration ratio is lower than 1:5, the obtained mercaptosulfonate gold salt has low stability and is prone to gold precipitation. If the molar concentration ratio is higher than 1:15, the cost is increased.

[0027] In a specific embodiment, the molar concentration of the gold complexing agent in the electroplating solution is 0.10 mol / L~0.60 mol / L; the molar concentration of the tin complexing agent in the electroplating solution is 0.05 mol / L~1.50 mol / L; and the concentration of the additive in the electroplating solution is 0.30 g / L~1.00 g / L.

[0028] In a specific embodiment, the molar concentration ratio of gold ions to gold complexing agent in the electroplating solution is 1:(8-20). Specifically, if the molar concentration ratio is lower than 1:8, the storage stability of the cyanide-free Au-Sn electroplating solution cannot meet the requirements, and if the molar concentration ratio is higher than 1:20, the cyanide-free Au-Sn electroplating solution is prone to precipitate crystals, thereby affecting the performance of the Au-Sn alloy plated parts.

[0029] In a specific embodiment, the molar concentration ratio of tin ions to tin complexing agents in the electroplating solution is 1:(2-8). Specifically, if the molar concentration ratio is lower than 1:2, the electroplating stability of the cyanide-free Au-Sn electroplating solution cannot meet the requirements, and it is impossible to obtain Au-Sn alloy-plated parts with uniform and stable components and high reproducibility during long-term storage or long-term electroplating. If the molar concentration ratio is higher than 1:8, the Au-Sn alloy-plated parts prepared by electroplating with the cyanide-free Au-Sn electroplating solution will have coarse grains.

[0030] In a specific embodiment, the mercaptosulfonic acid gold salt includes at least one of 2-mercaptoethanesulfonic acid gold salt, 3-mercapto-1-propanesulfonic acid gold salt, 2,3-dimercaptopropanesulfonic acid gold salt, 4-mercapto-1-butanesulfonic acid gold salt, 3,4-dimercaptobutanesulfonic acid gold salt and 2,4-dimercaptobutanesulfonic acid gold salt. Specifically, the mercaptosulfonic acid gold salt has high storage stability, the mercaptosulfonic acid salt can form a strong coordination bond with the gold ion, does not have the problem of easy decomposition by itself, and can be compatible with a variety of complexing agents and additives, so that the cyanide-free Au-Sn electroplating solution using the mercaptosulfonic acid salt system has high storage stability.

[0031] In a specific embodiment, the tin source is at least one of Sn(II) salt and / or Sn(IV) salt, preferably at least one of stannous chloride, stannous sulfate, stannous pyrophosphate, sodium stannate and potassium stannate.

[0032] In a specific embodiment, the gold complexing agent includes at least one of hydantoin, organic amine and amino acid. Specifically, the addition of the gold complexing agent can further improve the storage stability of the cyanide-free Au-Sn electroplating solution.

[0033] In a specific embodiment, the hydantoin includes at least one of 5,5-dimethylhydantoin, 1,5,5-trimethylhydantoin, 1-(hydroxymethyl)-5,5-dimethylhydantoin, 1,3-dihydroxymethyl-5,5-dimethylhydantoin and 2-thio-5,5-dimethylhydantoin.

[0034] In a specific embodiment, the organic amine includes at least one of ethylenediamine, propylenediamine, diethylenetriamine, tetraethylenepentamine, tetramethylethylenediamine, N-methylethylenediamine, N-ethylethylenediamine, N-propylethylenediamine, N-(2-hydroxyethyl)ethylenediamine, hydroxyethylethylenediaminetriacetic acid, ethylenediaminetetraacetic acid and ethylenediaminetetrapropionic acid.

[0035] In a specific embodiment, the amino acid includes at least one of glycine, alanine, aspartic acid, glutamic acid, cysteine, N-acetyl-L-cysteine ​​and glutathione.

[0036] In a specific embodiment, the tin complexing agent includes at least one of thioglycolic acid, potassium thioglycolate, sodium thioglycolate and ammonium thioglycolate. Specifically, the addition of thioglycolic acid and its salts can stabilize tin ions for a long time, inhibit the oxidation of Sn(II) to Sn(IV), and keep the deposition potential difference between Au and Sn stable for a long time, thereby obtaining Au-Sn alloy plated parts with uniform and stable composition and high reproducibility during long-term storage or long-term electroplating.

[0037] In a specific embodiment, the additive includes at least one of catechol, aminosulfonic acid, ascorbic acid, thiourea, thiosemicarbazide, nickel chloride, cobalt sulfate, polyethylene glycol and polyacetimide. Specifically, the addition of the additive can optimize the performance of the electroplating solution, further improve the dispersibility and covering ability of the cyanide-free Au-Sn electroplating solution, and enable it to effectively improve the performance of Au-Sn alloy plated parts within a wider range of pH and average current density.

[0038] In a specific embodiment, the pH buffer includes at least one of potassium dihydrogen phosphate, dipotassium hydrogen phosphate, sodium hydroxide and hydrochloric acid. Specifically, the addition of the pH buffer can adjust the electroplating solution to a specified pH, so that the electroplating solution maintains a stable pH.

[0039] Specifically, the cyanide-free Au-Sn electroplating solution of the present invention does not contain highly toxic substances, has high storage stability and electroplating stability, and can obtain Au-Sn alloy plated parts with uniform and stable composition and high reproducibility during long-term storage or long-term electroplating.

[0040] The present invention also discloses an application of the cyanide-free Au-Sn electroplating solution according to any embodiment of the present invention in preparing Au-Sn alloy plated parts.

[0041] In a specific embodiment, the application includes the following steps: immersing the part to be plated in a cyanide-free Au-Sn electroplating solution for electroplating to obtain an Au-Sn alloy plated part; wherein the electroplating temperature is 30°C~50°C; the average current density of the electroplating is 0.5ASD~10.0ASD; the electroplating method is direct current electroplating or periodic square wave pulse electroplating.

[0042] Specifically, the cyanide-free Au-Sn electroplating solution of the present invention has excellent electroplating performance and high cathode current efficiency, and can obtain high-performance Au-Sn alloy plated parts within a wide range of pH and average current density.

[0043] The present invention also discloses an application of a cyanide-free Au-Sn electroplating solution as in any embodiment of the present invention, or an Au-Sn alloy plated part obtained by application of any embodiment of the present invention in packaging technology of microelectronic or optoelectronic devices.

[0044] The following are specific embodiments Example 1 The cyanide-free Au-Sn electroplating solution of this embodiment includes components with the following concentrations: 0.02 mol / L 3-mercapto-1-propane sulfonic acid gold salt, 0.24 mol / L 5,5-dimethylhydantoin, 0.08 mol / L stannous pyrophosphate, 0.18 mol / L thioglycolic acid, 0.50 g / L catechol, 0.30 g / L polyethylene glycol and appropriate amounts of sodium hydroxide and dipotassium hydrogen phosphate. The pH of the cyanide-free Au-Sn electroplating solution is 7.

[0045] The preparation method of the cyanide-free Au-Sn electroplating solution of the present embodiment comprises the following steps: (1) Dissolve 2.00 g of gold flakes with a gold content of >99.99% in 14.00 g of aqua regia, and add deionized water to the resulting syrupy solution to remove nitrogen oxides to obtain a chloroauric acid solution, and adjust the pH of the chloroauric acid solution to 7 to obtain a first reaction solution.

[0046] (2) Dissolve 15.00 g of 3-mercapto-1-propane sulfonate in deionized water and adjust the pH of the solution to 9 to obtain a second reaction solution.

[0047] (3) The first reaction liquid and the second reaction liquid are mixed to obtain 3-mercapto-1-propanesulfonic acid gold salt.

[0048] (4) Mixing the 3-mercapto-1-propanesulfonic acid gold salt prepared in step (3) with 5,5-dimethylhydantoin to obtain a third reaction solution.

[0049] (5) Mix stannous pyrophosphate, thioglycolic acid, catechol and polyethylene glycol to obtain a fourth reaction solution.

[0050] (6) The third reaction solution and the fourth reaction solution are mixed, and sodium hydroxide and dipotassium hydrogen phosphate are added to the obtained mixed solution to adjust the pH value of the mixed solution to 7, thereby obtaining a cyanide-free Au-Sn electroplating solution.

[0051] The 3-mercapto-1-propane sulfonic acid gold salt solution prepared in this embodiment has high stability, remains clear and transparent in environments with changing temperature, humidity, light and oxidation, and does not produce precipitation or discoloration, and is not easy to react with other chemical substances.

[0052] The cyanide-free Au-Sn electroplating solution prepared in this embodiment does not contain highly toxic substances and can be stored at room temperature for more than 6 months. Even under high and low temperature changes, light, long-term storage or long-term electroplating, it still remains clear and transparent without precipitation generation or discoloration.

[0053] The deposition potential difference between Au and Sn in the cyanide-free Au-Sn electroplating solution prepared in this embodiment is small and remains stable during long-term storage or long-term electroplating. Figure 1 As shown, Figure 1 The linear sweep voltammetry curves of Au and Sn in the cyanide-free Au-Sn electroplating solution prepared in this embodiment.

[0054] The cyanide-free Au-Sn electroplating solution of this embodiment is used for electroplating, the electroplating anode is a platinum-titanium mesh, and the electroplating cathode is a silicon wafer with an Au seed layer sputtered on the surface. The anode and cathode are immersed in the electroplating solution of this embodiment for electroplating, and a periodic square wave pulse electroplating method is adopted, and the electroplating temperature is 40°C; the average current density of the electroplating is 1.5ASD and 6.0ASD, respectively, and Au-30.0±1.0at.%Sn eutectic plated parts and Au-45.0±1.0at.%Sn alloy plated parts with good bonding with the substrate, bright appearance, flatness and density, and low porosity can be obtained in a long time of electroplating, respectively, and have high electroplating stability.

[0055] Example 2 The cyanide-free Au-Sn electroplating solution of this embodiment includes components with the following concentrations: 0.03 mol / L 2-mercaptoethane sulfonate gold salt, 0.30 mol / L ethylenediaminetetraacetic acid, 0.05 mol / L stannous sulfate, 0.05 mol / L sodium stannate, 0.22 mol / L sodium thioglycolate, 0.60 g / L thiourea, 0.20 g / L nickel chloride and appropriate amounts of sodium hydroxide and potassium dihydrogen phosphate. The pH of the cyanide-free Au-Sn electroplating solution is 3.

[0056] The preparation method of the cyanide-free Au-Sn electroplating solution of the present embodiment comprises the following steps: (1) 3.00 g of gold flakes with a gold content of >99.99% were dissolved in 15.00 g of aqua regia, and deionized water was added to the obtained syrupy solution to remove nitrogen oxides, thereby obtaining a chloroauric acid solution. The pH of the chloroauric acid solution was adjusted to 6, thereby obtaining a first reaction solution.

[0057] (2) Dissolve 27.00 g of 2-mercaptoethane sulfonate in deionized water and adjust the pH of the solution to 12 to obtain a second reaction solution.

[0058] (3) The first reaction liquid and the second reaction liquid are mixed to obtain 2-mercaptoethanesulfonic acid gold salt.

[0059] (4) Mixing the 2-mercaptoethanesulfonic acid gold salt prepared in step (3) with ethylenediaminetetraacetic acid to obtain a third reaction solution.

[0060] (5) Mix stannous sulfate, sodium stannate, sodium thioglycolate, thiourea and nickel chloride to obtain a fourth reaction solution.

[0061] (6) The third reaction solution and the fourth reaction solution are mixed, and sodium hydroxide and potassium dihydrogen phosphate are added to the obtained mixed solution to adjust the pH value of the mixed solution to 3, thereby obtaining a cyanide-free Au-Sn electroplating solution.

[0062] The cyanide-free Au-Sn electroplating solution prepared in this embodiment does not contain highly toxic substances and can be stored at room temperature for more than 6 months. Even under high and low temperature changes, light, long-term storage or long-term electroplating, it still remains clear and transparent without precipitation generation or discoloration.

[0063] The cyanide-free Au-Sn electroplating solution of this embodiment is used for electroplating, the electroplating anode is a platinum titanium mesh, and the electroplating cathode is a silicon wafer with an Au seed layer sputtered on the surface. The anode and cathode are immersed in the electroplating solution of this embodiment for electroplating, and a direct current electroplating method is adopted. The electroplating temperature is 35°C; the average current density of the electroplating is 5.2ASD. After a long time of electroplating, Au-35.0±1.0at.%Sn alloy plated parts with good bonding with the substrate, bright appearance, flatness and density, and low porosity can be obtained, and have high electroplating stability.

[0064] Example 3 The cyanide-free Au-Sn electroplating solution of this embodiment includes components with the following concentrations: 0.01 mol / L 3,4-dimercaptobutane sulfonic acid gold salt, 0.15 mol / L glycine, 0.05 mol / L potassium stannate, 0.20 mol / L thioglycolic acid, 0.30 g / L ascorbic acid, 0.20 g / L thiosemicarbazide and appropriate amounts of sodium hydroxide and dipotassium hydrogen phosphate. The pH of the cyanide-free Au-Sn electroplating solution is 10.

[0065] The preparation method of the cyanide-free Au-Sn electroplating solution of the present embodiment comprises the following steps: (1) Dissolve 1.00 g of gold flakes with a gold content of >99.99% in 8.00 g of aqua regia, and add deionized water to the resulting syrupy solution to remove nitrogen oxides to obtain a chloroauric acid solution, and adjust the pH of the chloroauric acid solution to 6 to obtain a first reaction solution.

[0066] (2) Dissolve 10.00 g of 3,4-dimercaptobutane sulfonate in deionized water and adjust the pH of the solution to 10 to obtain a second reaction solution.

[0067] (3) The first reaction liquid and the second reaction liquid are mixed to obtain 3,4-dimercaptobutanesulfonic acid gold salt.

[0068] (4) Mixing the 3,4-dimercaptobutanesulfonic acid gold salt prepared in step (3) with glycine to obtain a third reaction solution.

[0069] (5) Potassium stannate, thioglycolic acid, ascorbic acid and thiosemicarbazide are mixed to obtain a fourth reaction solution.

[0070] (6) The third reaction solution and the fourth reaction solution are mixed, and sodium hydroxide and dipotassium hydrogen phosphate are added to the obtained mixed solution to adjust the pH value of the mixed solution to 10, thereby obtaining a cyanide-free Au-Sn electroplating solution.

[0071] The cyanide-free Au-Sn electroplating solution prepared in this embodiment does not contain highly toxic substances and can be stored at room temperature for more than 6 months. Even under high and low temperature changes, light, long-term storage or long-term electroplating, it still remains clear and transparent without precipitation generation or discoloration.

[0072] The cyanide-free Au-Sn electroplating solution of this embodiment is used for electroplating. The electroplating anode is a platinum-titanium mesh, and the electroplating cathode is a silicon wafer with a sputtered Au seed layer on the surface. The anode and cathode are immersed in the electroplating solution of this embodiment for electroplating. The periodic square wave pulse electroplating method is adopted. The electroplating temperature is 40°C; the average current density of the electroplating is 4.0ASD. After a long time of electroplating, Au-30.0±1.0at.%Sn eutectic plated parts with good bonding with the substrate, bright appearance, flatness and density, and low porosity can be obtained. It has high electroplating stability, such as Figure 2 As shown, Figure 2This is a composition change diagram of the Au-Sn alloy plated parts prepared when the average current density is 4.0ASD during long-term electroplating.

[0073] Comparative Example 1 The only difference between this comparative example and Example 1 is that 3-mercapto-1-propane sulfonic acid gold salt is changed to gold sulfite, and thioglycolic acid is changed to potassium pyrophosphate.

[0074] The cyanide-free Au-Sn electroplating solution prepared in this comparative example can be stored at room temperature for 2 months. After 2 months, black powder precipitation occurs and the solution becomes ineffective. This is because the gold sulfite itself is easily decomposed, resulting in low storage stability of the Au-Sn electroplating solution.

[0075] The cyanide-free Au-Sn electroplating solution prepared in this comparative example has a small deposition potential difference between Au and Sn on the first day, but cannot remain stable during long-term storage or long-term electroplating. Figure 3 As shown, Figure 3 This is the linear sweep voltammetry curve of Au and Sn in the cyanide-free Au-Sn electroplating solution prepared in this comparative example.

[0076] The cyanide-free Au-Sn electroplating solution of this comparative example was used for electroplating. The electroplating method was the same as that in Example 1. The average current density of the electroplating was 6.0 ASD. Au-45.7 at.% Sn alloy-plated parts were obtained on the first day, and Au-20.5 at.% Sn alloy-plated parts were obtained on the fifth day. The electroplating stability was poor.

[0077] Comparative Example 2 The only difference between this comparative example and Example 1 is that the mass of 3-mercapto-1-propane sulfonate in the second reaction solution is changed to 5.00 g.

[0078] The 3-mercapto-1-propane sulfonic acid gold salt solution prepared in this comparative example had poor stability, and a golden powder precipitated on the day of preparation, resulting in failure.

[0079] Comparative Example 3 The only difference between this comparative example and Example 1 is that the molar concentration of stannous pyrophosphate is changed to 0.20 mol / L.

[0080] The cyanide-free Au-Sn electroplating solution of this comparative example was used for electroplating. The electroplating method was the same as that of Example 1. The Sn content in the Au-Sn alloy-plated parts obtained within the average current density of 0.5ASD~10ASD was greater than 45.0at.%, and Au-Sn alloy-plated parts with other components could not be obtained.

[0081] Comparative Example 4 The only difference between this comparative example and Example 1 is that the molar concentration of 5,5-dimethylhydantoin is changed to 0.50 mol / L.

[0082] The cyanide-free Au-Sn electroplating solution prepared in this comparative example precipitated a large amount of white crystals during storage at room temperature.

[0083] Comparative Example 5 This comparative example is compared with Example 1, except that the molar concentration of thioglycolic acid is changed to 1.00 mol / L.

[0084] The cyanide-free Au-Sn electroplating solution of this comparative example was used for electroplating. The electroplating method was the same as that of Example 1. The Au-Sn alloy plated parts obtained within the average current density of 0.5ASD-10ASD all had coarse grains.

[0085] Comparative Example 6 The only difference between this comparative example and Example 1 is that catechol and polyethylene glycol are not added.

[0086] The cyanide-free Au-Sn electroplating solution of this comparative example was used for electroplating. The electroplating method was the same as that of Example 1. The Au-Sn alloy plated parts obtained within the average current density of 0.5ASD to 10ASD were partially burned and blackened, and had an uneven appearance.

[0087] The above-mentioned embodiments only express several implementation methods of the present invention, and the description thereof is relatively specific and detailed, but it cannot be understood as limiting the scope of the patent application. It should be pointed out that, for a person of ordinary skill in the art, several variations and improvements can be made without departing from the concept of the present invention, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be subject to the attached claims.

Claims

1. A cyanide-free Au-Sn electroplating solution, characterized in that: The electroplating solution is composed of a gold source, a tin source, a gold complexing agent, a tin complexing agent, an additive and a pH buffer; The amount of the gold source is such that the molar concentration of gold ions in the electroplating solution is 0.01 mol / L to 0.04 mol / L; The amount of the tin source is such that the molar concentration of tin ions in the electroplating solution is 0.02 mol / L to 0.20 mol / L; The gold source is mercaptosulfonate gold salt; The tin complexing agent is thioglycolic acid and its salt; The pH value of the cyanide-free Au-Sn electroplating solution is 3-11.

2. The cyanide-free Au-Sn electroplating solution according to claim 1, characterized in that: The molar concentration ratio of gold ions to tin ions in the electroplating solution is 1:(2-6).

3. The cyanide-free Au-Sn electroplating solution according to claim 1, characterized in that: The preparation method of the mercaptosulfonic acid gold salt comprises the following steps: (1) dissolving a gold flake having a gold content of more than 99.99% in aqua regia, and adding deionized water to the obtained syrupy solution to remove nitrogen oxides, thereby obtaining a chloroauric acid solution, and then adjusting the pH of the chloroauric acid solution to 6-7, thereby obtaining a first reaction solution; (2) dissolving the mercaptosulfonate in deionized water and adjusting the pH of the solution to 9-13 to obtain a second reaction solution; (3) The first reaction liquid and the second reaction liquid are mixed and reacted to obtain the mercaptosulfonic acid gold salt.

4. The cyanide-free Au-Sn electroplating solution according to claim 3, characterized in that: In step (1), the mass ratio of the gold flakes to aqua regia is 1:(5-10); In step (2), the mercaptosulfonate includes at least one of 2-mercaptoethanesulfonate, 3-mercapto-1-propanesulfonate, 2,3-dimercaptopropanesulfonate, 4-mercapto-1-butanesulfonate, 3,4-dimercaptobutanesulfonate and 2,4-dimercaptobutanesulfonate; In step (3), the molar concentration ratio of the gold ions in the first reaction solution to the mercaptosulfonate in the second reaction solution is 1:(5-15).

5. The cyanide-free Au-Sn electroplating solution according to claim 1, characterized in that: The molar concentration of the gold complexing agent in the electroplating solution is 0.10 mol / L~0.60 mol / L; the molar concentration of the tin complexing agent in the electroplating solution is 0.05 mol / L~1.50 mol / L; and the concentration of the additive in the electroplating solution is 0.30 g / L~1.00 g / L.

6. The cyanide-free Au-Sn electroplating solution according to claim 1, characterized in that: The molar concentration ratio of gold ions to the gold complexing agent in the electroplating solution is 1:(8-20); the molar concentration ratio of tin ions to the tin complexing agent in the electroplating solution is 1:(2-8).

7. The cyanide-free Au-Sn electroplating solution according to claim 1, characterized in that: The mercaptosulfonate gold salt includes at least one of 2-mercaptoethanesulfonate gold salt, 3-mercapto-1-propanesulfonate gold salt, 2,3-dimercaptopropanesulfonate gold salt, 4-mercapto-1-butanesulfonate gold salt, 3,4-dimercaptobutanesulfonate gold salt and 2,4-dimercaptobutanesulfonate gold salt; The tin source is at least one of Sn(II) salt and / or Sn(IV) salt; The gold complexing agent includes at least one of hydantoin, organic amine and amino acid; The tin complexing agent includes at least one of thioglycolic acid, potassium thioglycolate, sodium thioglycolate and ammonium thioglycolate; The additive comprises at least one of catechol, aminosulfonic acid, ascorbic acid, thiourea, thiosemicarbazide, nickel chloride, cobalt sulfate, polyethylene glycol and polyacetimide; The pH buffer includes at least one of potassium dihydrogen phosphate, dipotassium hydrogen phosphate, sodium hydroxide and hydrochloric acid.

8. Use of the cyanide-free Au-Sn electroplating solution as claimed in any one of claims 1 to 7 in preparing Au-Sn alloy plated parts.

9. The use according to claim 8, characterized in that: The application comprises the following steps: Immersing the workpiece to be plated in the cyanide-free Au-Sn electroplating solution for electroplating to obtain an Au-Sn alloy plated workpiece; The electroplating temperature is 30°C to 50°C; The average current density of the electroplating is 0.5ASD~10.0ASD; The electroplating method is direct current electroplating or periodic square wave pulse electroplating.

10. Use of the cyanide-free Au-Sn electroplating solution as claimed in any one of claims 1 to 7, or the Au-Sn alloy plated parts obtained by using the solution as claimed in any one of claims 8 to 9 in the packaging technology of microelectronic or optoelectronic devices.

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