JP3112513B2 - Gold salt solution for gold plating - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gold ammonium cyanide solution used for a gold salt for gold plating.

Gold salts used for gold plating include gold potassium cyanide, which has been used in many fields including the semiconductor industry. In the field of gold plating,
In the semiconductor-related industry, baths for depositing soft gold having good bonding properties in gold wire bonding and TAB technology are used, but in many cases, baths using potassium potassium cyanide are generally used. In a bath using potassium potassium cyanide, potassium accumulates in the bath as the bath runs,
At this time, there is a disadvantage that the hardness of the gold plating coating gradually increases due to the eutectoid phenomenon of potassium. However, in a bath using ammonium ammonium cyanide, the accumulation of ammonium ions does not occur because ammonia ions volatilize from the bath as ammonia, and the ammonium plating does not cause an eutectoid phenomenon. There is a feature that is. This feature is in good agreement with the aforementioned purpose of gold wire bonding in the semiconductor-related industry and the purpose of depositing soft gold with good bondability in TAB technology, and furthermore, since it does not contain alkali metal ions, it is effective in preventing migration and the like. It is predicted that there will be, and is expected as a next-generation plating bath. The gold ammonium cyanide solution used for the gold salt for gold plating of the present invention has been made to meet such a demand.

[0003]

2. Description of the Related Art The production of gold ammonium cyanide is disclosed in Japanese Patent Publication No. 48-39158 or US Pat.
No. 582269, for example, which is obtained by passing potassium potassium cyanide through an ion exchange resin which has been ammonium-substituted in advance. Gold ammonium cyanide is an unstable gold salt that decomposes into gold cyanide, ammonia, and hydrogen cyanide according to the formula (1).

[0004]

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In the case of using gold ammonium cyanide for plating, a method using a solution is simple, but decomposition proceeds due to storage or aging, and yellow precipitation of gold cyanide occurs in the solution. When this gold cyanide solution is used in a gold plating bath, bumps and pinholes are likely to occur. Therefore, it is necessary to remove gold cyanide by filtration or the like in advance. In the semiconductor industry, miniaturization of circuit patterns is progressing, and occurrence of bumps, pinholes, and the like may cause fatal defects. From such a point of view, it can be said that a contrivance to increase the stability of the gold salt solution for gold plating used in a bath using gold ammonium cyanide is an urgent need in industry.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to provide a gold salt solution for gold plating using gold ammonium cyanide, which hardly deteriorates even during long-term storage.

[0007]

The gold salt solution for gold plating using gold ammonium cyanide as a gold salt according to the present invention contains a small amount of ammonium cyanide in addition to gold ammonium cyanide and has a hydrogen ion concentration of 8 to 10 with aqueous ammonia. Coordinated in between. The addition of ammonium cyanide shifts the chemical equilibrium of formulas (2) and (3) and contributes to the stabilization of gold ammonium cyanide, thereby preventing the formation of gold cyanide.

[0008]

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Further, the ammonia water prevents volatilization of hydrogen cyanide and contributes to the improvement of the stability of ammonium cyanide.

[0010]

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By these actions, when ammonium cyanide and ammonia are contained in a gold plating solution containing gold ammonium cyanide as a gold salt, the stability of the gold ammonium cyanide is increased, and long-term storage is possible. Also, it is difficult for deterioration to occur. Ammonium cyanide and ammonia are suitable as stabilizers because they evaporate gradually without accumulating as the plating bath is used.

The reason why the concentration of ammonium cyanide is in the range of 0.005 to 1.0% is that if the concentration is 0.005% or less, the effect as a stabilizer does not last long and gold cyanide tends to precipitate. On the other hand, if the concentration is too high, the liquid balance of the plating bath may be lost when it is put into the plating bath. In the actual concentration adjustment, the ammonium cyanide concentration is 1% in proportion to the gold ammonium cyanide concentration.
It is preferable to set them in the front and rear directions, because the operation is easy and the liquid balance of the plating bath is not lost. However, this need not necessarily be in this range.

Adjusting the hydrogen ion concentration to between 8 and 10 with aqueous ammonia is not preferred at a hydrogen ion concentration of 8 or less, because hydrogen cyanide tends to volatilize, and as a result, gold ammonium cyanide is decomposed. Further, hydrogen cyanide is toxic, and it is better not to adjust the hydrogen ion concentration to 8 or less from the viewpoint of safety. At a hydrogen ion concentration of 10 or more, on the contrary, the volatilization of ammonia becomes intense and the odor is strong, which is not preferable. In addition, since ammonia is weakly alkaline, it is necessary to add a large amount of hydrogen in order to make the hydrogen ion concentration 10 or more, and the solution balance in the plating bath is easily lost.

[0014]

Example 1 This example shows a method for producing a product of the present invention containing gold ammonium cyanide. First, hydrogenation of the ion exchange resin is performed by passing 20 liters of dilute sulfuric acid (concentration: 5%) at SV = 2 through 3 liters of the cation exchange resin packed in a 5 liter column. Next, 40 liters of pure water are passed through to wash well, and the solution is circulated between the column and the tank while passing a 15% ammonium amide sulfate solution.
Due to the circulation, the hydrogen ion concentration of the solution gradually decreases.
By adjusting the content within the range, ammonium ionization of the ion exchange resin is performed. The resin is washed again with 60 liters of pure water to remove the ammonium amidosulfate solution remaining in the resin tower. Then, to obtain the product of the present invention, potassium gold cyanide
10 liters of a solution containing 15% and 0.15% of potassium cyanide are passed through an ion-exchange resin tower to cause a substitution reaction between potassium and ammonium in the ion-exchange resin tower. After passing the whole amount, 15 liters of pure water is passed through to push out the remaining liquid in the resin tower to obtain a product stock solution. The hydrogen ion concentration of the product stock solution is 5
Since it is about 7 to 7, aqueous ammonia is added to adjust the hydrogen ion concentration to a range of 8 to 10. The liquid thus obtained is
It contains about 5% ammonium cyanide and about 0.03% ammonium cyanide, and does not deposit cyanogen gold even after long-term storage.

[0015]

[Prior art 1] The difference between the embodiment and the prior art is that the composition of the liquid to be passed during the substitution reaction of potassium and ammonium and the addition of ammonia water make it possible to adjust the hydrogen ion concentration in the range of 8 to 10. is there. The operation was performed in the same manner as in Example 1 to adjust the composition of the liquid to be passed when the substitution reaction between potassium and ammonium was carried out to a potassium potassium cyanide solution having a concentration of 15%, and to adjust the hydrogen ion concentration by adding aqueous ammonia. Otherwise, a solution containing about 5% gold ammonium cyanide is formed. When stored in a container and stored for a long time, yellow precipitates of cyan gold can be gradually deposited.

[0016]

EXAMPLE 2 Ammonium cyanide contained 5.6% of gold ammonium cyanide, and 0.005, 0.03, 0.2 and 1.
100% of each solution containing 0% and adjusted to a hydrogen ion concentration of 8.4 was prepared, placed in a stoppered 300 ml Erlenmeyer flask, lightly stoppered, and placed in a 70 ° C water bath to perform an acceleration test. . After 24 hours, there was no change in the liquid in each container.

[0017]

[Conventional example 2] 100 ml of a solution having a hydrogen ion concentration of 6.6 containing 5.6% of gold ammonium cyanide was placed in a 300 ml conical stoppered Erlenmeyer flask, lightly stoppered and placed in a 70 ° C water bath, followed by an acceleration test. Was done. After 6 hours, a slight yellow precipitate was observed in the liquid in the container, and after 24 hours, the yellow precipitate had further increased.

[0018]

[Comparative Example 1] 100 ml of a solution containing 5.6% of gold ammonium cyanide, adjusted to 0.003% of ammonium cyanide, and adjusted to a hydrogen ion concentration of 8.4 was placed in a 300 ml Erlenmeyer flask with a stoppered stopper and lightly stoppered. Into a water bath at 70 ° C. to perform an accelerated test. After 24 hours, a slight yellow precipitate was observed in the liquid in the container.

[0019]

Comparative Example 2 100 ml of a solution containing 5.6% of gold ammonium cyanide and having a hydrogen ion concentration adjusted to 8.5 was mixed with a stoppered plug.
The mixture was placed in a 300 ml Erlenmeyer flask, lightly stoppered, and placed in a 70 ° C water bath to perform an acceleration test. After 24 hours, a slight yellow precipitate was observed in the liquid in the container.

[0020]

Example 3 contains 11.2% of gold ammonium cyanide, and contains 0.005, 0.03, 0.2 and 1.
100% of each solution containing 0% and adjusted to a hydrogen ion concentration of 9.7 was prepared, placed in a stoppered 300 ml Erlenmeyer flask, lightly stoppered, and placed in a 70 ° C water bath to perform an acceleration test. . After 24 hours, there was no change in the liquid in each container.

[0021]

As is clear from the above, the gold salt solution for gold plating of the present invention does not increase the hardness of the gold plating due to the eutectoid phenomenon of potassium, unlike the conventional gold salt solution. There is no precipitation of cyan gold, which causes the occurrence of bumps and pinholes, so that it is possible to obtain soft gold plating with good bonding properties, and there is an effect that there is no deterioration even during long-term storage.

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁷ , DB name) C25D 3/48

Claims (1)

(57) [Claims] 1. A gold salt solution for gold plating, comprising gold cyanide as a gold salt, containing 0.005 to 1.0% of ammonium cyanide, and adjusted to a hydrogen ion concentration of 8 to 10 with aqueous ammonia.