JPH0525678A - Gold salt solution for gold plating - Google Patents

Abstract

PURPOSE:To obtain a gold salt soln. for gold plating which does not degenerate even after storage over a long period of time by incorporating a prescribed amt. of ammonium cyanide as well as ammonium gold cyanide and carrying out pH adjustment. CONSTITUTION:This gold salt soln. for gold plating contains ammonium gold cyanide as the gold salt and 0.005-1% ammonium cyanide for stabilizing the ammonium gold cyanide and has been adjusted to pH 8-10 with an aq. ammonia soln. so as to prevent the decomposition of the ammonium cyanide and the generation of ammonia. This gold salt soln. gives soft gold plating having satisfactory solderability and can be stored over a long period of time without degenerating.

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.

The gold salt used for gold plating has conventionally been potassium gold cyanide, which is used in many fields including the semiconductor industry. In the field of gold plating,
In the semiconductor-related industry, a bath for depositing soft gold having good bondability in gold wire bonding and TAB technology is used, but in many cases, a bath using potassium gold cyanide is common. In a bath using potassium gold cyanide, potassium accumulates in the bath as the bath runs,
At that time, there is a drawback that the hardness of the gold-plated coating gradually increases due to the eutectoid phenomenon of potassium. However, in a bath of gold ammonium cyanide, ammonium ions volatilize as ammonia from the bath, so that accumulation does not occur, and ammonium does not cause the eutectoid phenomenon, so a gold-plated coating with a substantially constant hardness can be obtained even after long-term use. There is a feature to be. This feature is in good agreement with the purpose of depositing soft gold with good bondability in the gold wire bonding and TAB technology in the semiconductor-related industry described above, and since it does not contain alkali metal ions, it is effective in preventing migration. It is predicted to be present and is expected as the next generation plating bath. The gold ammonium cyanide solution used for the gold salt for gold plating of the present invention is made to meet such requirements.

[0003]

[Prior Art and its Problems] In producing ammonium gold cyanide, Japanese Patent Publication No. 48-39158 or US Pat.
No. 582269, for example, it can be obtained by passing potassium gold cyanide through an ion exchange resin which has been previously substituted with ammonium. Gold ammonium cyanide is an unstable gold salt and decomposes into gold cyanide, ammonia, and hydrogen cyanide according to the formula (1).

[0004]

[Chemical 1]

When ammonium gold cyanide is used for plating, the method using a solution is simple, but decomposition progresses due to storage and aging, and yellow precipitation of gold cyanide occurs in the solution. When this gold cyanide salt solution is used in a gold plating bath, spots, pinholes and the like 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 the occurrence of spots, pinholes, and the like may lead to fatal defects. From this point of view, it is an urgent industrial need to devise a method for increasing the stability of the gold salt solution for gold plating used in a bath containing gold ammonium cyanide.

[0006]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a gold salt solution for gold plating which uses gold ammonium cyanide as a gold salt, which is unlikely to deteriorate even after 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 ammonium gold cyanide and further has a hydrogen ion concentration of 8 to 10 with aqueous ammonia. Has been adjusted in between. The addition of ammonium cyanide shifts the chemical equilibrium of the formulas shown in Chemical formulas 2 and 3 and contributes to the stabilization of gold ammonium ammonium cyanide, so that the generation of cyanogen gold is prevented.

[0008]

[Chemical 2]

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

[0010]

[Chemical 3]

Due to these actions, when the gold salt solution for gold plating containing gold ammonium cyanide as a gold salt contains ammonium cyanide and ammonia, the stability of the gold ammonium cyanide is increased, and storage for a long period of time, etc. Even in the case of alteration, it is unlikely that alteration will occur. Ammonium cyanide and ammonia are suitable as stabilizers because they gradually evaporate without accumulating as the plating bath is used.

The reason for setting the concentration of ammonium cyanide in the range of 0.005 to 1.0% is that at a concentration of 0.005% or less, the effect as a stabilizer does not last long and gold cyanide easily precipitates. Further, if the concentration is too high, the liquid balance of the plating bath may be disturbed when it is added to the plating bath. In the actual concentration adjustment, the ammonium cyanide concentration is 1% in proportion to the ammonium gold cyanide concentration.
It is preferable to set it before and after, because the operation is easy and the liquid balance of the plating bath is not disturbed. However, this does not necessarily have to be in this range.

It is not preferable to adjust the hydrogen ion concentration to between 8 and 10 with aqueous ammonia because hydrogen cyanide concentration of 8 or less causes volatilization of hydrogen cyanide, resulting in decomposition of ammonium gold cyanide. Further, hydrogen cyanide is toxic, and it is better to avoid adjusting the hydrogen ion concentration to 8 or less from the viewpoint of safety. On the contrary, when the hydrogen ion concentration is 10 or more, the volatilization of ammonia becomes violent and the odor is strong, which is not preferable. Further, since ammonia is weakly alkaline, it is necessary to add a large amount in order to increase the hydrogen ion concentration to 10 or more, and it is easy to upset the liquid balance of the plating bath.

[0014]

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

[0015]

Conventional Example 1 The difference between the example and the conventional example is that the composition of the liquid to be passed when the substitution reaction of potassium and ammonium is carried out and whether the hydrogen ion concentration can be adjusted to the range of 8 to 10 by adding aqueous ammonia. is there. The same operation as in Example 1 was carried out, and the composition of the liquid passed when carrying out the substitution reaction of potassium with ammonium was a potassium gold cyanide solution with a concentration of 15%, and ammonia water was added to adjust the hydrogen ion concentration. If not, a solution containing about 5% ammonium gold cyanide results. If it is put in a container and stored for a long period of time, a yellow precipitate of cyan-gold can be gradually formed.

[0016]

Example 2 Ammonium cyanide 5.6% was added, and the amount of ammonium cyanide was 0.005, 0.03, 0.2, 1.
100 ml of each solution containing 0% and adjusted to a hydrogen ion concentration of 8.4 was prepared, placed in a 300 ml Erlenmeyer flask with a stopper, lightly stoppered and placed in a water bath at 70 ° C for an accelerated test. .. Even after 24 hours, there was no change in the liquid in each container.

[0017]

[Prior art example 2] 100 ml of a solution containing 5.6% of ammonium gold cyanide and having a hydrogen ion concentration of 6.6 is put in a 300 ml Erlenmeyer flask of a stopper type, lightly stoppered and put in a water bath at 70 ° C for an accelerated 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 was further increased.

[0018]

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

[0019]

[Comparative Example 2] 100 ml of a solution containing 5.6% ammonium gold cyanide and adjusted to have a hydrogen ion concentration of 8.5 was mixed with a stoppered system.
It was put in a 300 ml Erlenmeyer flask, lightly stoppered and put in a water bath at 70 ° C. to perform an acceleration test. After 24 hours, a slight yellow precipitate was found in the liquid in the container.

[0020]

Example 3 Ammonium gold cyanide was included at 11.2%, and ammonium cyanide was added at 0.005, 0.03, 0.2, 1.
100 ml of each solution containing 0% and adjusted to a hydrogen ion concentration of 9.7 was prepared, placed in a 300 ml Erlenmeyer flask with a stopper, lightly stoppered and placed in a 70 ° C water bath for an accelerated test. .. Even after 24 hours, there was no change in the liquid in each container.

[0021]

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

Claims (1)

Claim: What is claimed is: 1. A gold salt for gold plating, comprising gold ammonium cyanide as a gold salt, ammonium cyanide 0.005 to 1.0%, and ammonia water adjusted to have a hydrogen ion concentration of 8 to 10. solution.