JPH0347972A - Method for preventing decomposition of electroless gold plating solution - Google Patents

Abstract

PURPOSE:To prevent the decomposition of an electroless gold plating soln. and to excellently plate a material with gold without lowering the plating rate by circulating the soln. in which the material is dipped with a pump in plating. CONSTITUTION:An electroless gold plating soln. 2 contg. potassium gold cyanide, potassium cyanide, caustic potash and a boron-based reducing agent is charged in a plating tank 1, a material to be treated is dipped in the tank, and electroless gold plating is carried out. In this case, a part of the soln. 2 is continuously drawn off by a pump 3, again returned to the tank 1 and circulated. The circulation of soln. is preferably controlled to about 2-6 cycles/hr. Consequently, even if nickel, etc., are brought into the soln. by >= about 10ppm from the material, etc., the decomposition of the soln. 2 is prevented. Accordingly, the material is excellently electroless-plated with gold without lowering the plating rate.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention prevents the decomposition of an electroless gold plating solution containing potassium gold cyanide, potassium cyanide, potassium hydroxide, and a boronate reducing agent. Regarding the method.

[Prior art and problems to be solved by the invention] Conventionally, an alkaline electroless gold plating solution containing potassium gold cyanide, potassium cyanide, potassium hydroxide, and a boronate reducing agent has been used to coat electronic parts, etc. It is used for gold plating.

However, in this type of electroless gold plating solution, decomposition of the solution often occurs, and according to studies conducted by the present inventors, the cause of this is the contamination of impurities such as nickel. Therefore, in order to prevent the decomposition of the electroless gold plating solution mentioned above, it is sufficient to prevent impurities such as nickel from getting mixed in, but parts to be gold plated are often plated with nickel as a base plating, and from the nickel plating solution. The introduction of nickel impurities into the electroless gold plating solution is unavoidable.

Therefore, it is desirable to stabilize the electroless gold plating solution and prevent its decomposition even when nickel is mixed in as an impurity.

[Means and effects for solving the problem] As a result of intensive studies in order to meet the above-mentioned needs, the present inventors have developed potassium gold cyanide as described above.

Electroless gold plating solutions containing boron-based reducing agents such as potassium cyanide, potassium hydroxide, dimethylamine borane, and potassium borohydride may be contaminated with nickel, especially 10 ppm or more of nickel. During plating, the solution becomes unstable, the deposition rate decreases, precipitation stops, and the solution decomposes. However, if the plating solution is circulated with a pump during such plating, nickel may be mixed in. It has been found that the precipitation rate can be reduced or stopped, and furthermore, the decomposition of the liquid can be prevented. In this case, even if the liquid is agitated with air or stirred with a stirrer instead of circulating the liquid with a pump, it will not be possible to prevent the decomposition of the liquid or stop the precipitation, as is clear from the experiments described below. However, liquid decomposition and precipitation stoppage phenomena can be specifically prevented only when the liquid is circulated using a pump.

Therefore, the present invention provides a method for performing electroless gold plating by immersing a workpiece in an electroless gold plating solution containing potassium gold cyanide, potassium cyanide, potassium hydroxide, and a boron-based reducing agent. Plating is carried out while circulating with a pump,
Provided is a method for preventing decomposition of an electroless gold plating solution, which is characterized by preventing decomposition of the plating solution.

The present invention will be explained in more detail below.

In the present invention, the electroless gold plating solution to be stabilized is gold potassium cyanide (usually 0.005 to 0.0
．． 1 mol/fl), potassium cyanide (usually 0.001~
0.1 mol/Q), potassium hydroxide (usually 0.1-2 mol/Q)
Il) Contains a boronate reducing agent (usually 0.01 to 0.2 mol/Q), and further contains amines such as alkanolamines and ethylenediamine, accelerating stabilizers such as lead salts, etc. The pH is usually 10.
~14. As the boronate reducing agent, amine borane such as dimethylamine borane and hydrogenated boronates such as potassium borohydride can be used.

In addition, when gold plating is performed using such an electroless gold plating solution, the plating temperature is usually 50 to 90°C, but in the present invention, the gold plating method is to perform plating while circulating the plating solution with a pump. This is what we do. As shown in the drawing, a part of the electroless gold plating solution 2 contained in the plating tank 1 is continuously drawn out by the operation of the pump 3, and this is re-plated in the plating tank 1. Any method can be used as long as it returns to . In this case, the liquid circulation rate is preferably 2 to 6 revolutions/hour.

By adopting this pump circulation method, it is possible to apply good gold plating to the object to be plated without reducing the plating speed or decomposing the liquid, and the object to be plated can be plated with nickel as its base plating. When the object to be plated is immersed in the gold plating solution, there will be no problem even if the nickel plating solution from the previous process adhering to the object is brought into the gold plating solution in an amount of 10 ppm or more as nickel. It's something that doesn't exist.

EXAMPLES Hereinafter, the present invention will be specifically explained by showing Examples and Comparative Examples.

[Example, comparative example]

An electroless gold plating solution having the following composition was prepared.

Potassium gold cyanide 0.02 mol/Ω Potassium cyanide 0.1 Potassium hydroxide 0.2 Potassium borohydride 0.2 Lead chloride
3.5xlQ-6n Next, 20 ppm of nickel sulfate as metallic nickel was added to the above plating solution, and plating was performed at a temperature of 75°C in the stirring mode shown in Table 1, and the precipitation rate at that time and the presence or absence of decomposition of the plating solution were evaluated. Examined.

The results are shown in Table 1.

Table 1 Note that the deposition rate in the normal state in which nickel sulfate was not added to the above plating solution was 2.0 units/hr.

As is clear from the results in Table 1, air and nitrogen agitation,
When stirring with a stirrer, nickel gets mixed in and stops the deposition of the electroless gold plating solution or causes it to decompose, but only when liquid circulation using a pump is used can this specifically prevent liquid decomposition. Moreover, it can be seen that the precipitation rate is not reduced.

〔Effect of the invention〕

As explained above, according to the present invention, decomposition of an electroless gold plating solution containing potassium cyanide, potassium cyanide, potassium hydroxide, and a boronate reducing agent mixed with nickel impurities is reliably prevented. However, it is possible to deposit good gold plating without reducing the deposition rate.

[Brief explanation of drawings]

The drawing is a schematic sectional view showing an example of an apparatus used to implement the present invention. 1... Plating tank, 2... Electroless gold plating solution, 3
·pump. −

Claims (1)

[Claims] 1. When performing electroless gold plating by immersing the workpiece in an electroless gold plating solution containing potassium gold cyanide, potassium cyanide, potassium hydroxide, and a boron-based reducing agent, the plating solution is circulated with a pump while plating. 1. A method for preventing decomposition of an electroless gold plating solution, the method comprising: preventing decomposition of the plating solution.