Cyanide-free gold solution and its preparation method and application

Abstract

The invention relates to the field of electroplating, and discloses a cyanide-free gold solution and a preparation method and application thereof, wherein the cyanide-free gold solution comprises gold ions, sulfite ions, bisulfite ions, hydroxy thioether and nitrilotriacetic acid. The cyanide-free gold solution provided by the invention has high gold ion stability, is not easy to precipitate, and the hardness of the electroplated coating is soft, which meets the soft gold requirements of wafer packaging.

Description

Technical Field

[0001] The invention relates to the field of electroplating, and in particular to a cyanide-free gold solution and a preparation method and application thereof. Background Art

[0002] JP03146419A applies for a method for preparing a cyanide-free electroplating gold solution, the solution contains sodium gold sulfite or potassium gold sulfite, the pH value of the solution is controlled in the range of 6-7, and in the process of synthesizing gold hydroxide, the concentration of potassium hydroxide or sodium hydroxide is 25-50%, and the pH value of the titration endpoint is controlled in the range of 8-9. Since gold hydroxide is an amphoteric hydroxide, excessive control of the titration endpoint and excessive concentration of potassium hydroxide or sodium hydroxide will dissolve the precipitated gold hydroxide, resulting in a low conversion rate of the intermediate gold hydroxide formed.

[0003] JP2013224496A improves the stability of cyanide-free electroplating gold solution by optimizing and improving the synthesis process. After being placed at 20°C for 24 hours, the particle increase rate measured by storage is less than 20%. However, the ratio of sodium sulfite to gold added in this method is as high as 6.1:1, and a large amount of sulfite exists in the plating solution, which can indeed improve the stability of the plating solution. However, as the electroplating proceeds, a large amount of sulfite will accumulate in the plating solution, causing serious organic pollution, affecting the stress morphology of the coating, etc., making process control difficult. Summary of the invention

[0004] In order to overcome the problems in the prior art that the cyanide-free gold electroplating solution is easy to precipitate gold, the hardness of the electroplated coating is high, which does not meet the soft gold requirement of wafer packaging, and the conversion rate of chloroauric acid is low during the preparation process, the present invention provides a cyanide-free gold solution and a preparation method and application thereof. The cyanide-free gold solution has high stability, is not easy to precipitate gold, the hardness of the electroplated coating is low, which meets the soft gold requirement of wafer packaging, and the conversion rate of chloroauric acid is high during the preparation process.

[0005] In order to achieve the above object, the first aspect of the present invention provides a cyanide-free gold solution, which comprises gold ions, sulfite ions, bisulfite ions, hydroxy thioether and nitrilotriacetic acid.

[0006] A second aspect of the present invention provides a method for preparing a cyanide-free gold solution, comprising the following steps: (1) in the presence of a first solvent, mixing chloroauric acid and an alkaline solution, aging, standing, and separating and precipitating to obtain gold hydroxide; (2) Mixing gold hydroxide with sulfite, optionally bisulfite, optionally pyrosulfite, hydroxy sulfide, and nitrilotriacetic acid under heating conditions and in the presence of a second solvent to obtain a cyanide-free gold solution.

[0007] The third aspect of the present invention provides an application of the cyanide-free gold solution provided by the first aspect of the present invention or the cyanide-free gold solution prepared by the method provided by the second aspect of the present invention in electroplating.

[0008] The beneficial effects of the present invention are: The cyanide-free gold solution provided by the present invention contains hydroxy thioether and nitrilotriacetic acid, which can synergistically improve the stability of gold ions in the solution and make it difficult to precipitate. In addition, during the preparation of the cyanide-free gold solution, bisulfite and pyrosulfite are also added to convert more gold hydroxide into Au. + , reduce the hardness of the coating obtained by electroplating so that it meets the soft gold requirements of wafer packaging.

[0009] Furthermore, the present invention can further improve the conversion rate of chloroauric acid in the preparation process by step-by-step titration and controlling the pH value of the titration endpoint. DETAILED DESCRIPTION

[0010] The endpoints and any values ​​of the ranges disclosed in this article are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of each range, the endpoint values ​​of each range and the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this article.

[0011] In the present invention, unless otherwise specified, gold ions refer to Au 3+ and Au + , that is, no special distinction is made for the valence state of gold.

[0012] A first aspect of the present invention provides a cyanide-free gold solution, which comprises gold ions, sulfite ions, bisulfite ions, hydroxy thioether and nitrilotriacetic acid.

[0013] In the present invention, hydroxythioether and nitrilotriacetic acid can synergistically improve the stability of gold ions in the solution, making it difficult to precipitate. In addition, the sulfite ions and bisulfite ions in the cyanide-free gold solution can make Au + Not reoxidized to Au 3+ , thereby reducing the hardness of the electroplated coating so that it meets the soft gold requirements of wafer packaging.

[0014] According to a preferred embodiment of the present invention, the molar ratio of the gold ions to the hydroxy thioether is 1:0.05-0.5.

[0015] In the present invention, an appropriate amount of hydroxy thioether can improve the stability of the cyanide-free gold solution and prolong the number of days for gold precipitation. Too low or too high a content of hydroxy thioether will affect the stability of the cyanide-free gold solution to a certain extent.

[0016] More preferably, the molar ratio of the gold ions to the hydroxy thioether is 1:0.2-0.45.

[0017] According to the present invention, preferably, the molar ratio of the gold ions to the nitrilotriacetic acid is 1:0.04-0.5.

[0018] In the present invention, an appropriate amount of nitrilotriacetic acid can also improve the stability of the cyanide-free gold solution and extend the number of days for gold precipitation. Too low or too high a content of nitrilotriacetic acid will affect the stability of the cyanide-free gold solution to a certain extent.

[0019] More preferably, the molar ratio of the gold ion to the nitrilotriacetic acid is 1:0.15-0.35.

[0020] According to a preferred embodiment of the present invention, the molar ratio of the hydroxy thioether to the nitrilotriacetic acid is 0.3-6:1.

[0021] In the present invention, when the molar ratio of the hydroxy thioether to the nitrilotriacetic acid is within the above range, the stability of the cyanide-free gold solution can be further improved.

[0022] More preferably, the molar ratio of the hydroxy thioether to the nitrilotriacetic acid is 0.3-3:1.

[0023] According to the present invention, preferably, the gold ion content in the cyanide-free gold solution is 0.2-0.3 mol / L.

[0024] According to a preferred embodiment of the present invention, n 金离子 :(n 亚硫酸根离子 +n 亚硫酸氢根离子 ) =1:1-4; Among them, n 金离子 、n 亚硫酸盐 and n 亚硫酸氢盐 are respectively the molar amounts of gold ions, sulfite ions and bisulfite ions in the cyanide-free gold solution.

[0025] In the present invention, when the molar amounts of gold ions, sulfite ions and bisulfite ions are within the above ranges, Au can be better avoided. + It is re-oxidized and improves the stability of the plating solution, while preventing excessive sulfite from accumulating during continuous electroplating and affecting the performance of the coating.

[0026] More preferably, n 金离子 :(n 亚硫酸根离子 +n 亚硫酸氢根离子 ) =1:1.5-2.5.

[0027] According to a preferred embodiment of the present invention, the hydroxy thioether is at least one selected from thiodiglycol, 2-hydroxyethyl sulfide, 2-hydroxyethyl n-propyl sulfide and 2-hydroxyanisyl thioether.

[0028] In the present invention, when the hydroxy thioether is selected from the above range, the stability of the cyanide-free gold solution can be further improved.

[0029] More preferably, the hydroxy thioether is thiodiglycol.

[0030] According to a preferred embodiment of the present invention, the pH value of the cyanide-free gold solution is 9-11.

[0031] In the present invention, when the pH value of the cyanide-free gold solution is within the above range, the stability and electroplating effect of the cyanide-free gold solution can be better balanced.

[0032] In the present invention, the cyanide-free gold solution may contain other metal cations, such as Na + , K + wait.

[0033] A second aspect of the present invention provides a method for preparing a cyanide-free gold solution, comprising the following steps: (1) in the presence of a first solvent, mixing chloroauric acid and an alkaline solution, aging, standing, and separating and precipitating to obtain gold hydroxide; (2) Mixing gold hydroxide with sulfite, optionally bisulfite, optionally pyrosulfite, hydroxy sulfide, and nitrilotriacetic acid under heating conditions and in the presence of a second solvent to obtain a cyanide-free gold solution.

[0034] The present invention adds hydroxy thioether and nitrilotriacetic acid into the preparation method of the cyanide-free gold solution, and the two can synergistically improve the stability of gold ions in the solution.

[0035] Sulfite is not sufficient to completely convert gold hydroxide to Au + The inventors of the present invention have found that the addition of bisulfite and pyrosulfite can convert more gold hydroxide into Au + , until it is completely converted, thereby reducing the hardness of the electroplated coating to meet the soft gold requirements of wafer packaging and avoiding gold precipitation in the preparation process of the cyanide-free gold solution.

[0036] The present invention has no particular limitation on the specific types of the first solvent and the second solvent, and those skilled in the art may select the first solvent and the second solvent by conventional methods, for example, water.

[0037] According to a preferred embodiment of the present invention, in step (1), the method of mixing chloroauric acid and the alkaline solution is a first titration and a second titration performed sequentially; In the first titration, the hydroxide ion concentration of the alkaline solution is 5-12 mol / L, and the endpoint pH value of the first titration is 6-7.

[0038] The ratio of the hydroxide ion concentration of the alkaline solution in the first titration to the hydroxide ion concentration of the alkaline solution in the second titration is 1.5-2.5:1, and the endpoint pH value of the second titration is 7-8.

[0039] In the present invention, by step-by-step titration and controlling the pH value of the titration endpoint, the formation of gold hydroxide can be further promoted, and the re-dissolution of the formed gold hydroxide solid can be further avoided, thereby further improving the conversion rate of chloroauric acid in the preparation process.

[0040] More preferably, in the first titration, the hydroxide concentration of the alkaline solution is 8-11 mol / L, and the endpoint pH value of the first titration is 6.4-6.8. In the second titration, the hydroxide concentration of the alkaline solution is 4-6 mol / L, and the endpoint pH value of the second titration is 7.2-7.6.

[0041] The present invention does not particularly limit the dropping speed of the alkaline solution in the first titration and the second titration, and those skilled in the art can make conventional selections. According to a specific embodiment of the present invention, the dropping speed of the alkaline solution in the first titration and the second titration is independently 2-4 mL / min.

[0042] According to the present invention, preferably, the temperature at which the chloroauric acid and the alkaline solution are mixed is 10-50°C.

[0043] The present invention does not particularly limit the specific conditions of the aging, and those skilled in the art can routinely select. According to a specific embodiment of the present invention, in step (1), the aging temperature is 75-85° C. and the time is 0.5-4 h.

[0044] According to the present invention, specifically, the standing time is 4-24h.

[0045] According to the present invention, bicarbonate may be added during the aging process to stabilize the pH value of the mixture obtained in the buffering step (1). The bicarbonate may be sodium bicarbonate and / or potassium bicarbonate.

[0046] According to a preferred embodiment of the present invention, in step (2), the molar ratio of gold hydroxide to sulfite is 1:1.8-2.6.

[0047] According to the present invention, preferably, the molar ratio of the gold hydroxide to the bisulfite is 1:0.2-1.

[0048] According to the present invention, preferably, the molar ratio of the gold hydroxide to the pyrosulfite is 1:0.05-0.5.

[0049] In the present invention, when the molar ratio of gold hydroxide to sulfite, bisulfite, and pyrosulfite, especially the molar ratio of gold hydroxide to pyrosulfite, is within the above range, the Au 3+ Transformed to Au + , reducing the hardness of the coating obtained by electroplating.

[0050] More preferably, the molar ratio of the gold hydroxide to the sulfite, the bisulfite, and the pyrosulfite is 1:1.8-2.2:0.4-0.8:0.1-0.2.

[0051] The present invention does not particularly limit the cations of the sulfite, bisulfite and pyrosulfite, and those skilled in the art can routinely select. According to a specific embodiment of the present invention, the cations of the sulfite, bisulfite and pyrosulfite can be Na + and / or K + .

[0052] According to the present invention, preferably, the molar ratio of the gold hydroxide to the hydroxy thioether is 1:0.01-1.

[0053] According to the present invention, preferably, the molar ratio of the gold hydroxide to the nitrilotriacetic acid is 1:0.05-0.5.

[0054] In the present invention, when the concentrations of gold hydroxide, hydroxysulfide and nitrilotriacetic acid are respectively within the above ranges, the stability of gold ions in the solution can be further improved.

[0055] More preferably, the molar ratio of the gold hydroxide to hydroxy thioether and nitrilotriacetic acid is 1:0.06-0.5:0.15-0.35.

[0056] According to a preferred embodiment of the present invention, step (2) comprises: (2-1) mixing gold hydroxide with sulfite, and then mixing with hydroxy thioether and nitrilotriacetic acid at 70-80° C. in the presence of a second solvent, and reacting for 2-3 hours; (2-2) The substance obtained in step (2-1) is cooled to 55-65°C, bisulfite is added to react for 0.5-2h, and then pyrosulfite is added to react for 5-20h to obtain a cyanide-free gold solution.

[0057] In the present invention, the methods of steps (2-1) and (2-2) can further improve the stability of the system.

[0058] The third aspect of the present invention provides an application of the cyanide-free gold solution provided by the first aspect of the present invention or the cyanide-free gold solution prepared by the method provided by the second aspect of the present invention in electroplating.

[0059] The present invention will be described in detail below through examples.

[0060] In the following examples, the content of ions in the cyanide-free gold solution was measured using a Thermo Fisher Scientific iCAP PRO ICP-OES inductively coupled plasma emission spectrometer; The contents of sulfite ion, bisulfite ion, hydroxy thioether and nitrilotriacetic acid are calculated by the feed amount; The hardness of the coating was measured using a Mitutoyo precision hardness tester; The method for the aging test of the cyanide-free gold solution is to dilute the cyanide-free gold solution 4 times and then conduct it under the conditions of light intensity of 500 lux and temperature of 35°C.

[0061] Unless otherwise specified, all reagents and raw materials were purchased from commercial sources.

[0062] Examples 1-7 Take 130 mL of chloroauric acid aqueous solution with a gold content (in terms of gold) of 400 g / L, control the titration temperature, drip the first NaOH aqueous solution into the above chloroauric acid aqueous solution at a rate of 3 mL / min, and perform the first titration until the pH value of the liquid part of the mixture reaches the first titration endpoint. Switch to the second NaOH aqueous solution, continue to drip into the above mixture at a rate of 3 mL / min, and perform the second titration until the pH value of the liquid part of the mixture reaches the second titration endpoint.

[0063] The mixture obtained by titration was heated to 80°C, 2 g of sodium bicarbonate was added, and the mixture was kept warm for 30 min, cooled naturally and allowed to stand for 24 h, and the gold hydroxide precipitate was filtered. The mixture was washed and filtered with 500 mL of 0.1 wt% sodium bicarbonate aqueous solution, and the process was repeated three times.

[0064] Mix the washed gold hydroxide with 1.5L water, keep stirring, heat to 75℃ and keep, add sodium sulfite three times, each time with an interval of 15min, then add nitrilotriacetic acid and thiodiglycol in turn, and react for 2h. Cool to 65℃ and add sodium bisulfite, react for 1h. Then add sodium pyrosulfite and react for 8h to obtain a cyanide-free gold solution.

[0065] The pH of the cyanide-free gold solution was adjusted to 8.0 using 1 wt % dilute sulfuric acid and 10 wt % NaOH aqueous solution.

[0066] The titration temperature, the concentration of the first NaOH aqueous solution and the second NaOH aqueous solution, and the pH values ​​of the first titration endpoint and the second titration endpoint are shown in Table 1. The addition amounts of nitrilotriacetic acid, thiodiglycol, sodium sulfite, sodium bisulfite, and sodium pyrosulfate are shown in Table 2.

[0067] Table 1

[0068] Table 2

[0069] Example 8 A cyanide-free gold solution was prepared in the manner of Example 1, except that 14.5 g of dithioglycolic acid was used instead of thiodiglycol.

[0070] Comparative Example 1 A cyanide-free gold solution was prepared in the manner of Example 1, except that 12 g of thiodiglycolic acid was used instead of thiodiglycol, and sodium pyrosulfate was not added.

[0071] Comparative Example 2 A cyanide-free gold solution was prepared in the manner of Example 1, except that 11.5 g of triisopropanolamine was used instead of nitrilotriacetic acid, and sodium pyrosulfate was not added.

[0072] Test Example 1 The content of gold ions in the cyanide-free gold solutions obtained in the above examples and comparative examples was measured, and the contents of other components were calculated by the feed amounts. The results are shown in Table 3.

[0073] Table 3

[0074] Test Example 2 The cyanide-free gold solution obtained in the above examples and comparative examples was electroplated at a current of 0.4 ASD (ampere per square decimeter) for 20 minutes to obtain a gold coating. The coating was annealed at 220° C. for 30 minutes, and the hardness of the coating after annealing was measured. The results are shown in Table 4.

[0075] Table 4

[0076] Test Example 3 The cyanide-free gold solutions obtained in the above examples and comparative examples were subjected to aging tests, and the results are shown in Table 5.

[0077] Table 5

[0078] It can be seen from the results of Table 3 that the titration conditions will affect the conversion rate of chloroauric acid, and the preferred titration conditions of the present invention obtain a higher conversion rate of chloroauric acid. It can be seen from the results of Tables 4 and 5 that the cyanide-free gold solution provided by the present invention is more stable, less prone to gold precipitation, and the hardness of the coating obtained by electroplating is lower, which can meet the requirements of soft gold for wafer packaging.

[0079] The preferred embodiments of the present invention are described in detail above, but the present invention is not limited thereto. Within the technical concept of the present invention, the technical solution of the present invention can be subjected to a variety of simple modifications, including the combination of various technical features in any other suitable manner, and these simple modifications and combinations should also be regarded as the contents disclosed by the present invention and belong to the protection scope of the present invention.

Claims

1. A cyanide-free gold solution, characterized in that The cyanide-free gold solution comprises gold ions, sulfite ions, bisulfite ions, hydroxy thioether and nitrilotriacetic acid.

2. The cyanide-free gold solution according to claim 1, characterized in that The molar ratio of gold ions to hydroxy thioether is 1:0.05-0.5; And / or, the molar ratio of the gold ion to the nitrilotriacetic acid is 1:0.04-0.

5.

3. The cyanide-free gold solution according to claim 1 or 2, characterized in that The molar ratio of the hydroxy thioether to nitrilotriacetic acid is 0.3-6:1; And / or, the gold ion content in the cyanide-free gold solution is 0.2-0.3 mol / L.

4. The cyanide-free gold solution according to claim 1 or 2, characterized in that n 金离子 :(n 亚硫酸根离子 +n 亚硫酸氢根离子 ) =1:1-4; Among them, n 金离子 、n 亚硫酸盐 and n 亚硫酸氢盐 are respectively the molar amounts of gold ions, sulfite ions and bisulfite ions in the cyanide-free gold solution.

5. The cyanide-free gold solution according to claim 1 or 2, characterized in that The hydroxy thioether is selected from at least one of thiodiglycol, 2-hydroxyethyl sulfide, 2-hydroxyethyl n-propyl sulfide and 2-hydroxyanisyl thioether.

6. The cyanide-free gold solution according to claim 1 or 2, characterized in that The pH value of the cyanide-free gold solution is 9-11.

7. A method for preparing a cyanide-free gold solution, characterized in that: The following steps are involved: (1) in the presence of a first solvent, mixing chloroauric acid and an alkaline solution, aging, standing, and separating and precipitating to obtain gold hydroxide; (2) Mixing gold hydroxide with sulfite, optionally bisulfite, optionally pyrosulfite, hydroxy sulfide, and nitrilotriacetic acid under heating conditions and in the presence of a second solvent to obtain a cyanide-free gold solution.

8. The method according to claim 7, characterized in that In step (1), the method of mixing chloroauric acid and the alkaline solution is a first titration and a second titration performed sequentially; In the first titration, the hydroxide ion concentration of the alkaline solution is 5-12 mol / L, and the endpoint pH value of the first titration is 6-7; The ratio of the hydroxide ion concentration of the alkaline solution in the first titration to the hydroxide ion concentration of the alkaline solution in the second titration is 1.5-2.5:1, and the endpoint pH value of the second titration is 7-8; And / or, the temperature at which the chloroauric acid and the alkaline solution are mixed is 10-50°C.

9. The method according to claim 7 or 8, characterized in that: In step (1), the aging temperature is 75-85°C and the time is 0.5-4h; And / or, the standing time is 4-24h.

10. The method according to claim 7 or 8, characterized in that: In step (2), the molar ratio of gold hydroxide to sulfite is 1:1.8-2.6; and / or, the molar ratio of the gold hydroxide to the bisulfite is 1:0.2-1; and / or, the molar ratio of the gold hydroxide to the pyrosulfite is 1:0.05-0.5; And / or, the molar ratio of gold hydroxide to hydroxy thioether is 1:0.01-1; And / or, the molar ratio of the gold hydroxide to the nitrilotriacetic acid is 1:0.05-0.

5.

11. The method according to claim 7 or 8, characterized in that: Step (2) includes: (2-1) mixing gold hydroxide with sulfite, and then mixing with hydroxy thioether and nitrilotriacetic acid at 70-80° C. in the presence of a second solvent, and reacting for 2-3 hours; (2-2) The substance obtained in step (2-1) is cooled to 55-65°C, bisulfite is added to react for 0.5-2h, and then pyrosulfite is added to react for 5-20h to obtain a cyanide-free gold solution.

12. Use of the cyanide-free gold solution according to any one of claims 1 to 6 or the cyanide-free gold solution prepared by the method according to any one of claims 7 to 11 in electroplating.

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