JP2004307907A - Method for removing potassium ion from silver plating liquid - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for removing potassium ions from a silver plating liquid whose pH can be rapidly and safely adjusted. <P>SOLUTION: The method for removing the potassium ions from the silver plating liquid comprises bringing the silver plating liquid containing silver potassium cyanide as a supply source for silver into contact with a chelate resin in order to remove the potassium ions from the silver plating liquid increased in the potassium ions and made higher in the pH by precipitation of the silver by electrolytic plating. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method for removing potassium ions from a silver plating solution.
[0002]
[Prior art]
Electrolytic silver plating is often used for partial plating of inner leads and stage portions of lead frames for semiconductor devices.
As a plating solution for electrolytic silver plating, a cyan bath containing potassium silver cyanide as a supply source of silver is generally used.
The plating solution is managed by replenishing potassium silver cyanide when silver is consumed by electrolytic plating. Further, other chemicals gradually reduced by taking out the plating solution are appropriately replenished.
[0003]
By the way, silver in the plating solution is consumed, and if potassium silver cyanide is added to make up for this, potassium is inevitably accumulated in the plating solution, thereby increasing the pH.
The pH of the cyan bath is usually set to a weak alkali of 8 to 10, but if the pH is higher than this, there is a problem that the plating appearance is adversely affected. That is, when the pH is increased, silver is liable to be deposited by substitution, thereby causing plating unevenness and impairing the appearance. Further, in semi-glossy plating, gloss is more than necessary. Furthermore, there is a problem in that impurities such as copper and iron gradually increase in the form of a cyan complex in the solution, which adversely affects the plating appearance.
[0004]
Conventionally, when the pH has risen, a method of removing potassium ions using a semipermeable membrane or neutralizing with an acid such as citric acid or phosphoric acid to lower the pH has been adopted.
[0005]
[Problems to be solved by the invention]
However, the semipermeable membrane is susceptible to cyanide and cannot be used for a cyanide bath. In addition, in the method of neutralization with an acid, the electrolyte concentration increases and the viscosity of the solution increases, which causes a reduction in the current density to be used, thereby lowering the plating efficiency. Further, since the neutralization reaction occurs by adding the acid, the plating appearance becomes uneven immediately after the addition of the acid, and it takes time to resume the plating operation. Furthermore, in the case of a plating solution containing cyanide, a toxic cyan gas is generated by the addition of an acid, which causes a problem that the working environment is deteriorated.
Then, this invention is made to solve the said subject, and it aims at providing the method of removing potassium ion from the silver plating solution which can adjust pH quickly and safely.
[0006]
[Means for Solving the Problems]
In order to solve the above problems, the method for removing potassium ions from a silver plating solution according to the present invention is a silver plating solution containing potassium silver cyanide as a supply source of silver, wherein silver is deposited by electrolytic plating. The method is characterized in that a silver plating solution is brought into contact with a chelating resin in order to remove potassium ions from a silver plating solution having an increased pH due to an increase in potassium ions.
[0007]
The pH is adjusted to 8 to 10 by removing potassium ions.
After adding the chelating resin to the silver plating solution and bringing the silver plating solution into contact with the chelating resin, the silver plating solution may be filtered, or the silver plating solution may be passed through a column filled with the chelating resin. May be brought into contact with the chelating resin.
[0008]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, preferred embodiments of the present invention will be described in detail.
The composition of the silver cyanide plating solution is not particularly limited. One or more succinates may be contained. These conductive salts also function as pH buffers.
It is preferable to adjust the pH of the silver plating solution to a weak alkalinity of 8 to 10.
[0009]
As a brightener, a compound of As, Tl, Se, or Te is used.
As these brighteners, potassium arsenite, sodium arsenite, thallium sulfate, thallium formate, selenium dioxide, potassium selenocyanate, telluric acid, tellurium dioxide and the like are suitable.
These brighteners are added in necessary amounts depending on the glossiness of the plating film to be obtained, but are preferably in the range of generally 0.005 to 50 mg / l, most preferably in the range of 0.01 to 5 mg / l.
[0010]
Further, a surfactant may be added as needed. As these surfactants, nonionic surfactants having a polyoxyethylene chain or fluorine-based surfactants are suitable, and these surfactants may be added at about 0.001 to 10 g / l.
[0011]
In the present invention, a silver plating solution containing the above-mentioned silver potassium cyanide as a supply source of silver, in which silver is precipitated by electrolytic plating, potassium ions are increased, and the pH is increased. The method is characterized in that a silver plating solution is brought into contact with a chelating resin in order to remove potassium ions.
[0012]
A chelate resin (including a chelate fiber) is a resin which strongly and selectively adsorbs a specific ion by chelate bond. Preferably, a chelate fiber ICP-S manufactured by Kyrest Co., Ltd. and Diaion CR11 manufactured by Mitsubishi Chemical Corporation are used. Can be used.
[0013]
By bringing the silver plating solution into contact with the chelating resin, potassium ions increased in the plating solution are selectively adsorbed and removed by the chelating resin.
By removing potassium ions in this manner, the pH can be adjusted to the initial value of 8 to 10.
[0014]
To selectively adsorb potassium ions to the chelating resin and remove it from the plating solution, add the chelating resin to the silver plating solution, contact the silver plating solution with the chelating resin, and adsorb potassium ions, The silver plating solution can be removed by filtration.
Alternatively, the silver plating solution can be removed by passing the solution through a column filled with a chelate resin so as to contact the chelate resin.
[0015]
During the use of the silver plating solution, impurity metals such as copper and iron gradually accumulate in the form of a cyan complex in the solution. However, by bringing the silver plating solution into contact with the chelating resin, these impurity metals are also reduced to the chelating resin. And can be removed.
The chelate resin to which potassium ions and impurity metals have been adsorbed is washed with an acid such as hydrochloric acid or sulfuric acid, whereby potassium ions and impurity metals are easily released and regenerated. Is also very advantageous.
[0016]
【Example】
Example 1
An example of the composition of the silver plating solution is shown.
80g / l potassium silver cyanide
Tripotassium citrate 100g / l
Potassium selenocyanate 0.001g / l
Polyethylene glycol 0.1 g / l
A silver plating solution having the above composition, which is used for silver plating, is supplemented with silver potassium cyanide as silver is consumed, and the pH gradually increases to about 10 in a beaker. The sample was collected, 200 g of Kyrest Fiber ICP-S manufactured by Kyrest Co., Ltd. was added, and the mixture was stirred with a magnetic stirrer. When the pH was measured 3 minutes after the addition of the chirest fiber, the pH dropped to pH 9.0 and decreased by 1. Flame analysis of the silver plating solution before and after the addition of the killing fiber showed that the potassium ion concentration was 50 g / l before the addition, but was halved to 25 g / l after the addition. In addition, no cyan gas was generated at the time of addition of the crest fiber (chelate resin). When the plating appearance was measured by a Hull cell test after the treatment, a favorable plating appearance was obtained.
[0017]
Example 2
To 1 liter of the silver plating solution, 100 g / l of Diaion CR11 manufactured by Mitsubishi Chemical Corporation was added in place of Killest Fiber ICP-S, followed by stirring with a magnetic stirrer. When the pH was measured 3 minutes after adding the diamond ion, the pH was lowered to 9.3. Flame analysis of the silver plating solution before and after the addition of diamond ions revealed that the potassium ion concentration was 50 g / l before the addition, but dropped to 30 g / l after the addition. Further, when diamond ions were added, generation of cyan gas was not observed at all. When the plating appearance was measured by a Hull cell test after the treatment, a favorable plating appearance was obtained.
[0018]
Comparative Example An acid was added to the silver plating solution to lower the pH by 1. However, since the silver plating solution contained cyan, cyan gas was generated. One hour after the acid addition, a Hull cell test was performed. As a result, significant unevenness occurred in the Hull cell plating pattern. When the Hull cell test was performed again with the silver plating solution left for one day after the addition of the acid, a uniform appearance without unevenness was obtained. Further, when the potassium ion concentration was analyzed by flame light analysis, there was no change of 50 g / l before and after the treatment.
[0019]
【The invention's effect】
As described above, according to the present invention, the pH can be quickly adjusted, and after the adjustment, there is no unevenness in the plating appearance. Therefore, the plating operation can be restarted immediately and the operation efficiency can be improved.
In addition, it is safe because no toxic cyan gas is generated.
Further, if the silver plating solution is passed through a column filled with a chelate resin, continuous processing can be performed.

Claims (4)

To remove potassium ions from a silver plating solution containing silver potassium cyanide as a supply source of silver, wherein potassium ions increase due to the deposition of silver by electrolytic plating and the pH has increased, A method for removing potassium ions from a silver plating solution, comprising bringing the silver plating solution into contact with a chelating resin. The method for removing potassium ions from a silver plating solution according to claim 1, wherein the pH is adjusted to 8 to 10 by removing potassium ions. 3. The method for removing potassium ions from a silver plating solution according to claim 1, wherein a chelating resin is added to the silver plating solution to bring the silver plating solution into contact with the chelating resin, and then the silver plating solution is filtered. . The method for removing potassium ions from a silver plating solution according to claim 1 or 2, wherein the silver plating solution is passed through a column filled with a chelating resin.