A cyanide-free Au-Sn electroplating solution and its application

Abstract

The present invention discloses a cyanide-free Au-Sn electroplating solution and its application, belonging to the field of electroplating technology. 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 gold source is a gold salt of mercapto sulfonic acid, and the tin complexing agent is mercaptoacetic acid and its salts. The pH of the cyanide-free Au-Sn electroplating solution is 3-11. The electroplating solution provided by the present invention does not contain highly toxic substances, has high storage stability and electroplating stability, and remains clear and transparent even after high and low temperature changes, light exposure, long-term storage, or long-term electroplating. A Au-Sn alloy plating with uniform and stable composition and high reproducibility can be obtained during long-term storage or long-term electroplating, thus effectively ensuring the performance of the Au-Sn alloy plating obtained by electroplating. The electroplating solution has excellent performance and is conducive to application in the packaging technology of microelectronic or optoelectronic devices.

Description

Technical Field

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

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

[0003] Traditional Au-Sn electroplating processes usually adopt cyanide systems. Although they have the advantages of high storage stability, long service life, high electroplating stability, and excellent properties of Au-Sn alloy electroplated parts, cyanides are highly toxic substances and do not meet the requirements of green electroplating and sustainable development. Therefore, non-cyanide Au-Sn electroplating systems that are non-toxic and pollution-free are gradually replacing cyanide Au-Sn electroplating systems.

[0004] The reasons for the instability of cyanide-free Au-Sn electroplating solutions are mainly the following three points: First, Sn(II) is easily oxidized to form hydrolyzable Sn(IV) and form precipitates; second, Au(I) is easily disproportionated to produce Au precipitates; third, Au(I) or Au(III) easily reacts spontaneously with Sn(II) to form Au precipitates. As a result, the currently used cyanide-free Au-Sn electroplating systems still have the following two problems: First, the storage stability of the Au-Sn electroplating solution is low and the service life is short. The components of the electroplating solution decompose during storage and then form precipitates. Chinese patents with publication numbers CN107287629A and CN102644098A both disclose a sulfite-based cyanide-free Au-Sn electroplating solution, but sulfite ions are prone to decomposition problems, causing gold ions to lose ligands and undergo disproportionation reactions to form gold precipitates, resulting in the failure of the Au-Sn electroplating solution. Second, the electroplating stability is low, and the reproducibility of high-performance Au-Sn eutectic electroplated parts is poor. The composition of the Au-Sn alloy electroplated parts obtained during long-term storage or long-term electroplating changes continuously. The US patent with publication number US2003134142A1 discloses a chloride-citric acid-based cyanide-free Au-Sn electroplating solution, but black precipitates containing gold, tin, and oxygen elements are formed after 3 days, resulting in a gradual decrease in the Sn content in the Au-Sn alloy electroplated parts within 3 days, leading to the failure of the Au-Sn electroplating solution. Summary of the Invention

[0005] The object of the present invention is to overcome the above-mentioned defects existing in the prior art, and to provide a cyanide-free Au-Sn electroplating solution and its application. By using gold mercaptosulfonate which does not contain highly toxic substances and a specific tin complexing agent, the stability of gold ions and tin ions is improved, thereby enhancing the storage stability and electroplating stability of the Au-Sn electroplating solution. A Au-Sn alloy plating with uniform and stable composition and high reproducibility can be obtained during long-term storage or long-term electroplating. At the same time, through the synergistic effect among the gold complexing agent, the additive and the pH buffer, the performance of the Au-Sn alloy plating is effectively improved.

[0006] To achieve the above object, the technical solution of the present invention is as follows:

[0007] A cyanide-free Au-Sn electroplating solution, which is composed of a gold source, a tin source, a gold complexing agent, a tin complexing agent, an additive and a pH buffer; the dosage 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 dosage 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 gold mercaptosulfonate; the tin complexing agent is mercaptoacetic acid and its salts; the pH of the cyanide-free Au-Sn electroplating solution is 3 to 11.

[0008] The present invention also discloses an application of the cyanide-free Au-Sn electroplating solution as described above in the preparation of Au-Sn alloy plating.

[0009] The present invention also discloses an application of the cyanide-free Au-Sn electroplating solution as described above, or the Au-Sn alloy plating obtained by the application as described above in the packaging technology of microelectronic or optoelectronic devices.

[0010] Implementing the embodiments of the present invention will have the following beneficial effects:

[0011] The gold mercaptosulfonate used in the cyanide-free Au-Sn electroplating solution provided by the present invention has high storage stability. Mercaptosulfonate can form strong coordination bonds with gold ions, is not easily affected by environmental factors such as temperature, humidity, light and oxidation, and does not have the problem of easy self-decomposition, ensuring the stability of gold ions, and thus ensuring the high storage stability of the cyanide-free Au-Sn electroplating solution. In addition, the gold mercaptosulfonate 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 plating obtained by electroplating. At the same time, the preparation method of gold mercaptosulfonate is simple, with high conversion rate, stable and efficient.

[0012] In the cyanide-free Au-Sn electroplating solution provided by the present invention, mercaptoacetic acid and its salts used can stabilize tin ions and inhibit the oxidation of Sn(II) to Sn(IV). It not only inhibits the formation of tin-containing precipitates, 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 an Au-Sn alloy plating with uniform and stable composition and high reproducibility.

[0013] The cyanide-free Au-Sn electroplating solution provided by the present invention does not contain highly toxic substances and has high storage stability. It can be stably stored at room temperature for more than 6 months. Even under conditions such as high and low temperature changes, light, long-term storage or long-term electroplating, it still remains clear and transparent, and no precipitation or discoloration occurs.

[0014] The cyanide-free Au-Sn electroplating solution provided by the present invention has high electroplating stability. The electroplating effect of the Au-Sn electroplating solution after long-term storage or long-term electroplating is the same as that of the newly prepared Au-Sn electroplating solution. The obtained Au-Sn alloy plating has uniform and stable composition and high reproducibility, and no problems such as self-decomposition of the composition or failure of the Au-Sn electroplating solution occur.

[0015] The cyanide-free Au-Sn electroplating solution provided by the present invention has excellent performance, good dispersion ability and covering ability, high cathode current efficiency, and can obtain high-performance Au-Sn alloy plating within a wide range of pH and average current density.

[0016] The composition of the Au-Sn alloy plating obtained by electroplating with the cyanide-free Au-Sn electroplating solution provided by the present invention includes, but is not limited to, the eutectic alloy composition of Au-30.0 at.% Sn. The composition deviation of the plating is less than 1.0%. After long-term electroplating, the composition of the Au-Sn alloy plating is stable, and it has good bonding force with the substrate, bright appearance, flat, dense and low porosity, which is beneficial to the application in the packaging technology of microelectronic or optoelectronic devices. Description of the Drawings

[0017] Figure 1 It is the linear sweep voltammetry 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 with the electrode potential of the saturated calomel electrode).

[0018] Figure 2 It is the composition change diagram of the Au-Sn alloy plating prepared at an average current density of 4.0 ASD during long-term electroplating in Example 3 of the present invention.

[0019] Figure 3 It is the linear sweep voltammetry 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 with the electrode potential of the saturated calomel electrode). Detailed Description of the Invention

[0020] The present invention will be further described below in conjunction with specific embodiments, but the present invention is not limited in any way.

[0021] The present invention discloses a cyanide-free Au-Sn electroplating solution, which is composed of a gold source, a tin source, a gold complexing agent, a tin complexing agent, an additive and a pH buffer; the dosage of the gold source makes the molar concentration of gold ions in the electroplating solution 0.01 mol / L to 0.04 mol / L; the dosage of the tin source makes the molar concentration of tin ions in the electroplating solution 0.02 mol / L to 0.20 mol / L; the gold source is gold mercaptosulfonate; the tin complexing agent is mercaptoacetic acid and its salts; the pH of the cyanide-free Au-Sn electroplating solution is 3 to 11.

[0022] In a specific embodiment, the molar concentration ratio of gold ions to tin ions in the electroplating solution is 1:(2 to 6). Specifically, if the molar concentration ratio is lower than 1:2, the Sn content is too low, and only the Au5Sn phase alloy (Au-16.7 at.% Sn) can be electroplated. If the molar concentration ratio is higher than 1:6, the Sn content is too high, and only the AuSn phase alloy (Au-50.0 at.% Sn) can be electroplated.

[0023] In a specific embodiment, the preparation method of gold mercaptosulfonate includes the following steps:

[0024] (1) Dissolve a gold sheet with a gold content > 99.99% in aqua regia, and add deionized water to the obtained syrupy solution to remove nitrogen oxides to obtain a chloroauric acid solution. Subsequently, adjust the pH of the chloroauric acid solution to 6 to 7 to obtain a first reaction solution.

[0025] (2) Dissolve the mercaptosulfonate in deionized water and adjust the pH of the solution to 9 to 13 to obtain a second reaction solution.

[0026] (3) Mix the first reaction solution and the second reaction solution for reaction to obtain gold mercaptosulfonate.

[0027] In a specific embodiment, in step (1), the mass ratio of the gold sheet to aqua regia is 1:(5 to 10).

[0028] 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.

[0029] In a specific embodiment, in step (3), the molar concentration ratio of gold ions in the first reaction solution to mercaptosulfonate in the second reaction solution is 1:(5 - 15). Specifically, if the molar concentration ratio is lower than 1:5, the resulting gold mercaptosulfonate has low stability and is prone to precipitate gold. If the molar concentration ratio is higher than 1:15, the cost increases.

[0030] 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; the concentration of the additive in the electroplating solution is 0.30 g / L - 1.00 g / L.

[0031] In a specific embodiment, the molar concentration ratio of gold ions to the 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. If the molar concentration ratio is higher than 1:20, the cyanide-free Au-Sn electroplating solution is prone to precipitate crystals, which in turn affects the performance of the Au-Sn alloy plating.

[0032] In a specific embodiment, the molar concentration ratio of tin ions to the tin complexing agent 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 a homogeneous, stable and highly reproducible Au-Sn alloy plating during long-term storage or long-term electroplating. If the molar concentration ratio is higher than 1:8, the grains of the Au-Sn alloy plating prepared by electroplating with the cyanide-free Au-Sn electroplating solution are coarse.

[0033] In a specific embodiment, the gold mercaptosulfonate includes at least one of gold 2-mercaptoethanesulfonate, gold 3-mercapto-1-propanesulfonate, gold 2,3-dimercaptopropanesulfonate, gold 4-mercapto-1-butanesulfonate, gold 3,4-dimercaptobutanesulfonate, and gold 2,4-dimercaptobutanesulfonate. Specifically, the gold mercaptosulfonate has high storage stability. The mercaptosulfonate can form strong coordination bonds with gold ions, has no problem of self-decomposition, and can be compatible with various complexing agents and additives, making the cyanide-free Au-Sn electroplating solution using the mercaptosulfonate system have high storage stability.

[0034] In a specific embodiment, the tin source is at least one of Sn(II) salts and / or Sn(IV) salts. Preferably, it is at least one of stannous chloride, stannous sulfate, stannous pyrophosphate, sodium stannate, and potassium stannate.

[0035] 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.

[0036] 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.

[0037] 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, hydroxyethylenediaminetriacetic acid, ethylenediaminetetraacetic acid, and ethylenediaminetetrapropionic acid.

[0038] 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.

[0039] In a specific embodiment, the tin complexing agent includes at least one of mercaptoacetic acid, potassium mercaptoacetate, sodium mercaptoacetate, and ammonium mercaptoacetate. Specifically, the addition of mercaptoacetic 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, so as to obtain a Au-Sn alloy plating with uniform and stable composition and high reproducibility during long-term storage or long-term electroplating.

[0040] In a specific embodiment, the additive includes at least one of catechol, sulfamic 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 dispersion ability and covering ability of the cyanide-free Au-Sn electroplating solution, and enable it to effectively improve the performance of the Au-Sn alloy plating within a wide range of pH and average current density usage.

[0041] 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 and keep the acidity and alkalinity of the electroplating solution stable.

[0042] 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 a Au-Sn alloy plating with uniform and stable composition and high reproducibility during long-term storage or long-term electroplating.

[0043] The present invention also discloses an application of a cyanide-free Au-Sn electroplating solution according to any embodiment of the present invention in the preparation of Au-Sn alloy plated parts.

[0044] In a specific embodiment, the application includes 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 part; wherein, the electroplating temperature is 30°C to 50°C; the average current density of electroplating is 0.5 ASD to 10.0 ASD; the electroplating method is direct current electroplating or periodic square wave pulse electroplating.

[0045] Specifically, the cyanide-free Au-Sn electroplating solution of the present invention has excellent electroplating performance and high cathode current efficiency, and high-performance Au-Sn alloy plated parts can be obtained within a wide range of pH and average current density.

[0046] The present invention also discloses an application of a cyanide-free Au-Sn electroplating solution according to any embodiment of the present invention, or an Au-Sn alloy plated part obtained by the application according to any embodiment of the present invention in the packaging technology of microelectronic or optoelectronic devices.

[0047] The following are specific examples

[0048] Example 1

[0049] The cyanide-free Au-Sn electroplating solution of this example includes components with the following concentrations:

[0050] 0.02 mol / L of gold 3-mercapto-1-propane sulfonate, 0.24 mol / L of 5,5-dimethylhydantoin, 0.08 mol / L of stannous pyrophosphate, 0.18 mol / L of mercaptoacetic acid, 0.50 g / L of catechol, 0.30 g / L of polyethylene glycol, and appropriate amounts of sodium hydroxide and dipotassium hydrogen phosphate, and the pH of the cyanide-free Au-Sn electroplating solution is 7.

[0051] The preparation method of the cyanide-free Au-Sn electroplating solution of this example includes the following steps:

[0052] (1) Dissolve 2.00 g of a gold sheet with a gold content >99.99% in 14.00 g of aqua regia, and add deionized water to the obtained syrup-like 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.

[0053] (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.

[0054] (3) Mix the first reaction solution and the second reaction solution to obtain gold 3-mercapto-1-propane sulfonate.

[0055] (4) Mix the gold 3-mercapto-1-propanesulfonate prepared in step (3) with 5,5-dimethylhydantoin to obtain a third reaction solution.

[0056] (5) Mix stannous pyrophosphate, mercaptoacetic acid, catechol and polyethylene glycol to obtain a fourth reaction solution.

[0057] (6) Mix the third reaction solution and the fourth reaction solution, and add sodium hydroxide and dipotassium hydrogen phosphate to the obtained mixed solution to adjust the pH of the mixed solution to 7 to obtain a cyanide-free Au-Sn electroplating solution.

[0058] The gold 3-mercapto-1-propanesulfonate solution prepared in this example has high stability, and remains clear and transparent in changing environments such as temperature, humidity, light, and oxidation, without precipitation or color change, and is not prone to reaction with other chemical substances.

[0059] The cyanide-free Au-Sn electroplating solution prepared in this example does not contain highly toxic substances, can be stored at room temperature for more than 6 months, and remains clear and transparent even under conditions such as high and low temperature changes, light, long-term storage, or long-term electroplating, without precipitation or color change.

[0060] The cyanide-free Au-Sn electroplating solution prepared in this example has a small deposition potential difference between Au and Sn, and remains stable during long-term storage or long-term electroplating. As Figure 1 shown, Figure 1 This is the linear sweep voltammetry curve of Au and Sn in the cyanide-free Au-Sn electroplating solution prepared in this example.

[0061] When electroplating using the cyanide-free Au-Sn electroplating solution of this example, the electroplating anode is a platinum-titanium mesh, and the electroplating cathode is a silicon wafer sputtered with an Au seed layer on the surface. Immerse the anode and cathode in the electroplating solution of this example for electroplating, and use a periodic square wave pulse electroplating method. The electroplating temperature is 40 °C; the average current density of electroplating is 1.5 ASD and 6.0 ASD. During long-term electroplating, eutectic Au-30.0 ± 1.0 at.% Sn plated parts and Au-45.0 ± 1.0 at.% Sn alloy plated parts with good adhesion to the substrate, bright appearance, flat, dense, and low porosity can be obtained, with high electroplating stability.

[0062] Example 2

[0063] The cyanide-free Au-Sn electroplating solution of this example includes components with the following concentrations:

[0064] 0.03 mol / L of gold 2-mercaptoethanesulfonate, 0.30 mol / L of ethylenediaminetetraacetic acid, 0.05 mol / L of stannous sulfate, 0.05 mol / L of sodium stannate, 0.22 mol / L of sodium thioglycolate, 0.60 g / L of thiourea, 0.20 g / L of nickel chloride, and appropriate amounts of sodium hydroxide and potassium dihydrogen phosphate. The pH of the cyanide-free Au-Sn electroplating solution is 3.

[0065] The preparation method of the cyanide-free Au-Sn electroplating solution in this example includes the following steps:

[0066] (1) Dissolve 3.00 g of gold flakes with a gold content > 99.99% in 15.00 g of aqua regia, and add deionized water to the obtained syrup-like solution to remove nitrogen oxides to obtain a chloroauric acid solution. Adjust the pH of the chloroauric acid solution to 6 to obtain the first reaction solution.

[0067] (2) Dissolve 27.00 g of 2-mercaptoethanesulfonate in deionized water and adjust the pH of the solution to 12 to obtain the second reaction solution.

[0068] (3) Mix the first reaction solution and the second reaction solution to obtain gold 2-mercaptoethanesulfonate.

[0069] (4) Mix the gold 2-mercaptoethanesulfonate prepared in step (3) with ethylenediaminetetraacetic acid to obtain the third reaction solution.

[0070] (5) Mix stannous sulfate, sodium stannate, sodium thioglycolate, thiourea, and nickel chloride to obtain the fourth reaction solution.

[0071] (6) Mix the third reaction solution and the fourth reaction solution, and add sodium hydroxide and potassium dihydrogen phosphate to the obtained mixed solution to adjust the pH of the mixed solution to 3 to obtain the cyanide-free Au-Sn electroplating solution.

[0072] The cyanide-free Au-Sn electroplating solution prepared in this example does not contain highly toxic substances and can be stored at room temperature for more than 6 months. Even under conditions such as high and low temperature changes, light, long-term storage, or long-term electroplating, it still remains clear and transparent, and no precipitation or color change occurs.

[0073] When electroplating using the cyanide-free Au-Sn electroplating solution in this example, the electroplating anode is a platinum-titanium mesh, and the electroplating cathode is a silicon wafer with an Au seed layer sputtered on its surface. Immerse the anode and cathode in the electroplating solution of this example for electroplating. Using the direct current electroplating method, the electroplating temperature is 35 °C; the average current density of electroplating is 5.2 ASD. An Au-35.0 ± 1.0 at.% Sn alloy plating part with good adhesion to the substrate, bright appearance, flat, dense, and low porosity can be obtained during long-term electroplating, and it has high electroplating stability.

[0074] Example 3

[0075] The cyanide-free Au-Sn electroplating solution of this example includes components with the following concentrations:

[0076] 0.01 mol / L of gold 3,4-dimercaptobutanesulfonate, 0.15 mol / L of glycine, 0.05 mol / L of potassium stannate, 0.20 mol / L of mercaptoacetic acid, 0.30 g / L of ascorbic acid, 0.20 g / L of thiosemicarbazide, and appropriate amounts of sodium hydroxide and dipotassium hydrogen phosphate. The pH of the cyanide-free Au-Sn electroplating solution is 10.

[0077] The preparation method of the cyanide-free Au-Sn electroplating solution of this example includes the following steps:

[0078] (1) Dissolve 1.00 g of a gold sheet with a gold content > 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. Adjust the pH of the chloroauric acid solution to 6 to obtain a first reaction solution.

[0079] (2) Dissolve 10.00 g of 3,4-dimercaptobutanesulfonate in deionized water and adjust the pH of the solution to 10 to obtain a second reaction solution.

[0080] (3) Mix the first reaction solution and the second reaction solution to obtain gold 3,4-dimercaptobutanesulfonate.

[0081] (4) Mix the gold 3,4-dimercaptobutanesulfonate prepared in step (3) with glycine to obtain a third reaction solution.

[0082] (5) Mix potassium stannate, mercaptoacetic acid, ascorbic acid, and thiosemicarbazide to obtain a fourth reaction solution.

[0083] (6) Mix the third reaction solution and the fourth reaction solution, and add sodium hydroxide and dipotassium hydrogen phosphate to the resulting mixed solution to adjust the pH of the mixed solution to 10 to obtain a cyanide-free Au-Sn electroplating solution.

[0084] The cyanide-free Au-Sn electroplating solution prepared in this example does not contain highly toxic substances and can be stored at room temperature for more than 6 months. Even under conditions such as high and low temperature changes, light, long-term storage, or long-term electroplating, it remains clear and transparent, and no precipitation or color change occurs.

[0085] Electroplating is carried out using the cyanide-free Au-Sn electroplating solution of this embodiment. The electroplating anode is a platinum-titanium mesh, and the electroplating cathode is a silicon wafer with an Au seed layer sputtered on its 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, and the electroplating temperature is 40 °C; the average current density of electroplating is 4.0 ASD. During long-term electroplating, an Au-30.0 ± 1.0 at.% Sn eutectic plating part with good adhesion to the substrate, bright appearance, flat, dense, and low porosity can be obtained, having high electroplating stability. As Figure 2 shown, Figure 2 Figure 4 is a composition change diagram of the Au-Sn alloy plating part prepared at an average current density of 4.0 ASD during long-term electroplating.

[0086] Comparative Example 1

[0087] Compared with Example 1, this comparative example is only different in that: the gold 3-mercapto-1-propane sulfonate is changed to gold sulfite, and the mercaptoacetic acid is changed to potassium pyrophosphate.

[0088] The cyanide-free Au-Sn electroplating solution prepared in this comparative example can be stored at room temperature for 2 months, and black powder precipitates and fails after 2 months. This is because gold sulfite is prone to decomposition by itself, resulting in low storage stability of the Au-Sn electroplating solution.

[0089] In the cyanide-free Au-Sn electroplating solution prepared in this comparative example, the deposition potential difference between Au and Sn is small on the first day, but it cannot remain stable during long-term storage or long-term electroplating. As Figure 3 shown, Figure 3 Figure 5 is the linear sweep voltammetry curve of Au and Sn in the cyanide-free Au-Sn electroplating solution prepared in this comparative example.

[0090] Electroplating is carried out using the cyanide-free Au-Sn electroplating solution of this comparative example. The electroplating method is the same as that of Example 1, and the average current density of electroplating is 6.0 ASD. An Au-45.7 at.% Sn alloy plating part is obtained on the first day of electroplating, and an Au-20.5 at.% Sn alloy plating part is obtained on the fifth day of electroplating. The electroplating stability is poor.

[0091] Comparative Example 2

[0092] Compared with Example 1, this comparative example is only different in that: the mass of 3-mercapto-1-propane sulfonate in the second reaction solution is changed to 5.00 g.

[0093] The 3-mercapto-1-propane sulfonate solution prepared in this comparative example has poor stability, and golden powder precipitates and fails on the day of preparation.

[0094] Comparative Example 3

[0095] This comparative example is different from Example 1 only in that: the molar concentration of stannous pyrophosphate is changed to 0.20 mol / L.

[0096] When electroplating using the cyanide-free Au-Sn electroplating solution of this comparative example, the electroplating method is the same as that of Example 1. The Sn content in the Au-Sn alloy plated parts obtained at an average current density of 0.5 ASD to 10 ASD is greater than 45.0 at.%, and Au-Sn alloy plated parts with other compositions cannot be obtained.

[0097] Comparative Example 4

[0098] This comparative example is different from Example 1 only in that: the molar concentration of 5,5-dimethylhydantoin is changed to 0.50 mol / L.

[0099] A large amount of white crystals precipitate during the storage of the cyanide-free Au-Sn electroplating solution prepared in this comparative example at room temperature.

[0100] Comparative Example 5

[0101] This comparative example is different from Example 1 only in that: the molar concentration of mercaptoacetic acid is changed to 1.00 mol / L.

[0102] When electroplating using the cyanide-free Au-Sn electroplating solution of this comparative example, the electroplating method is the same as that of Example 1. The Au-Sn alloy plated parts obtained at an average current density of 0.5 ASD to 10 ASD all have coarse grains.

[0103] Comparative Example 6

[0104] This comparative example is different from Example 1 only in that: catechol and polyethylene glycol are not added.

[0105] When electroplating using the cyanide-free Au-Sn electroplating solution of this comparative example, the electroplating method is the same as that of Example 1. The Au-Sn alloy plated parts obtained at an average current density of 0.5 ASD to 10 ASD are locally burned and blackened, and the appearance is uneven.

[0106] The above-mentioned embodiments only represent several implementation manners of the present invention. The description is relatively specific and detailed, but it should not be construed as a limitation to the scope of the patent application. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several modifications and improvements can still be made, and these all belong to the protection scope of the present invention. Therefore, the protection scope of this invention patent shall be subject to the appended claims.

Claims

1. A preparation method of a cyanide-free Au-Sn electroplating solution, characterized in that, Preparation method of cyanide-free Au-Sn electroplating solution, comprising the following steps: (1) Dissolve 3.00 g of gold flakes with gold content > 99.99% in 15.00 g of aqua regia, and add deionized water to the obtained syrup-like solution to remove nitrogen oxides, obtaining chloroauric acid solution, adjusting the pH of the chloroauric acid solution to 6 to obtain the first reaction solution; (2) Dissolve 27.00 g of 2-mercaptoethanesulfonate in deionized water, adjust the pH of the solution to 12 to obtain the second reaction solution; (3) Mix the first reaction solution and the second reaction solution to obtain 2-mercaptoethanesulfonic acid gold salt; (4) Mix the 2-mercaptoethanesulfonic acid gold salt prepared in step (3) with ethylenediaminetetraacetic acid to obtain the third reaction solution; (5) Mix stannous sulfate, sodium stannate, sodium mercaptoacetate, thiourea and nickel chloride to obtain the fourth reaction solution; (6) Mix the third reaction solution and the fourth reaction solution, and add sodium hydroxide and potassium dihydrogen phosphate to the obtained mixed solution to adjust the pH of the mixed solution to 3 to obtain the cyanide-free Au-Sn electroplating solution; In the cyanide-free Au-Sn electroplating solution, the concentration of 2-mercaptoethanesulfonic acid gold salt is 0.03 mol / L, the concentration of ethylenediaminetetraacetic acid is 0.30 mol / L, the concentration of stannous sulfate is 0.05 mol / L, the concentration of sodium stannate is 0.05 mol / L, the concentration of sodium mercaptoacetate is 0.22 mol / L, the concentration of thiourea is 0.60 g / L, the concentration of nickel chloride is 0.20 g / L, and the pH of the cyanide-free Au-Sn electroplating solution is 3.

2. Application of the cyanide-free Au-Sn electroplating solution prepared by the preparation method as claimed in claim 1 in the preparation of Au-Sn alloy plated parts.

3. The application according to claim 2, characterized in that, The said application comprises the following steps: Immerse the workpiece to be plated in the said cyanide-free Au-Sn electroplating solution for electroplating to obtain an Au-Sn alloy plated part; The temperature of the said electroplating is 30°C to 50°C; The average current density of the said electroplating is 0.5 ASD to 10.0 ASD; The said electroplating method is direct current electroplating or periodic square wave pulse electroplating.

4. Application of the cyanide-free Au-Sn electroplating solution prepared by the preparation method as claimed in claim 1 in the packaging technology of microelectronic or optoelectronic devices.

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