JPH1088399A - Electrolytic silver stripping agent, stripping solution and electrolytic stripping method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To electrolytically strip silver efficiently without using a cyan agent by using an aq. soln. contg. an aliphatic org. acid and its salt as a stripping soln. SOLUTION: This electrolytic stripping soln. contains an aliphatic org. acid and at least one kind of its salt as the effective components and prepared by dissolving an electrolytic silver stripping agent contg. a nonionic surfactant, as required, as the auxiliary component in water. The soln. is controlled to pH 4-14, a material to be stripped is dipped in the soln., and electrolysis is conducted at 10-80 deg.C and 0.5-10A/dm<2> current density with the material as an anode. Consequently, silver is electrolytically stripped efficiently without damaging the base metal, the stability of the effective components is increased in the soln., the bath life is prolonged, and safety is enhanced.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrolytic stripping agent for silver, a stripping solution, and an electrolytic stripping method. The present invention relates to a silver electrolytic peeling method using the same.

[0002]

2. Description of the Related Art In general, when a semiconductor chip mounting portion (so-called pad portion) is subjected to partial plating of silver in an electronic component such as a lead frame, the plating is performed only on a necessary portion by masking a plating unnecessary portion. I have to. However, even if such a masking process is performed, plating is formed by protruding beyond a required portion,
Peeling may be required. In such a case, an object to be stripped is immersed in a stripping solution, and an unnecessary portion of the plating film is stripped by anodic electrolysis.

As such a stripping solution, a solution containing a cyan compound such as sodium cyanide and potassium cyanide has been known for a long time. However, the cyan compound is highly toxic, and is highly toxic. Care must be taken when handling, as problems arise in safety management and the like. In addition, the characteristics of this solution are that the material metal is corroded, and excessive etching occurs on the surface of the required silver-plated portion.

In recent years, several cyanide-type strippers have been reported, but each has its own problems. For example,
Japanese Patent Publication No. 87587/1993 discloses a stripping solution containing succinimide and / or phthalic imide and an alkali metal hydroxide as main components. Is unstable in an aqueous solution, and its effect is significantly reduced due to hydrolysis and the like.
There is a drawback that the bath life becomes extremely short and the applicable pH range is narrow.

Japanese Patent Application Laid-Open No. 2-175825 discloses barbituric acid, uracil, glutarimide,
One or more compounds selected from a 5-membered ring and a 6-membered cyclized compound having -NH-, such as pyrrolidone, 3-pyrrolidone, 2-pyrrolidone-5-carboxylic acid, and proline, as a main component, and an alkali component, Strippers containing surfactants have been reported, but these base agents have a weak complexing effect with the stripping metal and form insoluble metal hydroxides in the bath. Since the reliability of the characteristics is reduced, the bath life is short and long-term use is not possible.

Further, Japanese Patent Application Laid-Open No. 7-243100 discloses a stripper containing a hydantoin compound. However, since the stripper specifically attacks the silver-plated portion, unevenness in gloss occurs in the silver pad portion. Depending on the shape of the processed product,
There is a problem that the usable current density range is restricted.

[0007]

The inventor of the present invention has conducted intensive studies to solve the problems of the prior art as described above. As a result, the aqueous solution containing an aliphatic organic acid and a salt thereof as an active ingredient was peeled off. By using as a liquid, it has been found that silver can be efficiently electrolytically peeled off without damaging the base metal, and that the effective component of the peeling liquid has high stability in the liquid and a long bath life, and has led to the present invention. Was.

That is, the present invention provides an electrolytic stripping agent for silver containing at least one of an aliphatic organic acid and a salt thereof, and, if necessary, a nonionic surfactant as an auxiliary component. The pH of the electrolytic stripping solution of silver and the electrolytic stripping solution consisting of an aqueous solution to be removed is adjusted to pH 4 to 14, and the object to be stripped is immersed in the solution.
It is intended to provide a method for electrolytically exfoliating silver, characterized in that electrolysis is carried out in an operating range of 0 ° C. and a current density of 0.5 to 10 A / dm ² .

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION Electrolytic stripping agent The electrolytic stripping agent of the present invention can be used as an aqueous silver stripping solution by converting it into an aqueous solution. The electrolytic stripping agent of the present invention contains an aliphatic organic acid or a salt thereof as an active ingredient. The aliphatic organic acids or salts thereof can be used alone or as a mixture of two or more. The aliphatic organic acid or salt thereof is not particularly limited as long as it is soluble in the stripping solution.
About 10 to about 10 can be used, and specifically, acetic acid, lactic acid, succinic acid, tartaric acid, malic acid, citric acid, gluconic acid, glycolic acid and alkali metal salts thereof such as potassium and sodium can be used.

Although the electrolytic stripping agent of the present invention has a sufficient stripping performance only with the active ingredient, a nonionic surfactant or the like can be used in combination as an auxiliary component, if necessary. The nonionic surfactant is not particularly limited as long as it is soluble in the stripping solution. For example, the nonionic surfactant has a molecular weight of 200 to 20,000.
A degree of polyethylene glycol can be used. By adding a nonionic surfactant such as polyethylene glycol, it is possible to selectively peel off only silver without further roughening the underlying metal surface when used as an electrolytic stripping solution for silver. It is possible to prevent the metal from floating in the bath when praying on the cathode surface.

As other auxiliary components, aliphatic aminocarboxylic acids or salts thereof can be used. The aliphatic aminocarboxylic acids or salts thereof can be used alone or as a mixture of two or more. By adding an aliphatic aminocarboxylic acid or an alkali metal salt thereof, when used as an electrolytic stripping solution for silver, bath conductivity is improved, and stable stripping performance can be maintained.

The aliphatic aminocarboxylic acid or a salt thereof is not particularly limited as long as it is soluble in a stripping solution.
Those having an aliphatic chain having about 1 to 10 carbon atoms can be used, and specifically, glycine, glycylglycine, glycylglycylglycine, glycylalanine, alanine, aminobutyric acid, aminocaproic acid, valine, leucine, isoleucine , Serine, threonine, cysteine, cystine, methionine, aspartic acid, glutamic acid, lysine and arginine and their alkali metal salts such as potassium and sodium, hydrochlorides, sulfates and acetates can be used.

[0013] The electrolytic stripping agent of the present invention includes NaOH, KOH
The pH of the aqueous solution can be adjusted by adding an alkali metal hydroxide such as If necessary, a pH buffer such as boric acid, potassium borate, and sodium borate can be added.

Electrolytic Stripping Solution The electrolytic stripping solution of the present invention corresponds to an aqueous solution of the electrolytic stripping agent of the present invention. Therefore, the electrolytic stripping solution of the present invention contains an aliphatic organic acid or a salt thereof as an active ingredient, and optionally contains a nonionic surfactant, an aliphatic organic acid or a salt thereof as an auxiliary ingredient. The aliphatic organic acids or salts thereof can be used alone or as a mixture of two or more. The content of the aliphatic organic acid and its salt can be 10 to 300 g / l, preferably 50 to 150 g / l. 10g / l
If it is not sufficient, sufficient bath conductivity cannot be obtained, and a sufficient peeling effect cannot be obtained. On the other hand, if it exceeds 300 g / l, the solubility approaches the saturated state, so that the solubility decreases, which is uneconomical.

The content of the nonionic surfactant is from 0.1 to
It can be 50 g / l, preferably 1 to 10 g / l. If it is less than 0.1 g / l, a sufficient effect cannot be obtained, and
If it exceeds 0 g / l, it is uneconomical and not preferable.
The content of the aliphatic aminocarboxylic acid and its salt is 5 to 30.
0 g / l, preferably 10 to 50 g / l. If it is less than 5 g / l, a sufficient effect cannot be obtained, and 300
If the amount is more than g / l, the solubility will decrease due to the approach of the saturated state, which is not economical and is not preferred.

The pH of the electrolytic stripping solution of the present invention is preferably 4 to 14, preferably 6 to 10, and if necessary, an alkali metal hydroxide such as sodium hydroxide or potassium hydroxide and an active ingredient. It can be adjusted using certain aliphatic organic acids. If the pH is lower than the above range, stable peeling performance may not be obtained due to etching of the base metal. If necessary, a pH buffer such as boric acid, potassium borate, and sodium borate can be added.

Electrolytic Stripping Method By using the electrolytic stripping solution of the present invention, silver on the base metal can be stripped efficiently. The electrolytic stripping method of the present invention, when subjected to silver plating on copper or copper alloy,
It is particularly effective for selectively removing silver plating applied to unnecessary portions.

The electrolytic stripping solution is adjusted to pH 4 to 14, and the object to be stripped is immersed in the solution.
Electrolysis is performed in an operating range of 0 to 80 ° C and a current density of 0.5 to 10 A / dm ² . The liquid temperature can be used in a wide range of 10 to 80 ° C, but 15 to 40 ° C is preferable. The anode current density at the time of peeling can be used in a wide range of 0.5 to 10 A / dm ² and is not particularly limited. However, when the anode current density falls below this range, the time required for peeling becomes longer, which is not preferable. Is not preferred because

[0019]

According to the present invention, silver can be efficiently electrolytically peeled off without using a cyanide compound, and the material metal is not adversely affected in a wide operation range. Unnecessary portions of the silver film can be peeled off without damaging the silver-plated portions, so that bath management is easy. The release agent of the present invention,
The safety is higher than the conventional release agent, and the release liquid has a long life.

[0020]

The present invention will be described in more detail with reference to the following examples. 3x5cm copper plate with polished surface (material)
Then, a 1.1 × 1.1 cm partial silver strike plating was performed, and a 1 × 1 cm silver plating having a thickness of 5 μm was formed thereon, and used for the following tests. The cathode was made of stainless steel.

Example 1 Using an aqueous solution (stripping solution) having a citric acid content of 100 g / l adjusted to pH 7.5 using NaOH and using a test piece as an anode, a current of 1 A / dm ² at 30 ° C. 1 in density
After electrolysis for a minute, only the protruding strike silver-plated portion could be peeled off without attacking the material copper surface.
A similar stripping test was performed after leaving the stripping solution for 2 weeks. The stripping solution had good stripping performance, and no change in pH or precipitation was observed.

Example 2 Using an aqueous solution (stripping liquid) having a sodium gluconate content of 40 g / l and a potassium sodium tartrate content of 50 g / l adjusted to pH 8.5 using KOH,
When the test piece was used as an anode and electrolyzed at a current density of 5 A / dm ² at 20 ° C. for 30 seconds, the material copper surface was not attacked.
Only the protruding strike silver-plated portion could be peeled off. A similar stripping test was performed after leaving the stripping solution for 2 weeks. The stripping solution had good stripping performance, and no change in pH or precipitation was observed.

Example 3 A sodium malate content of 40 g / l and an alanine content of 50 g / l adjusted to pH 7.5 using KOH
Using an aqueous solution (stripping solution), the test piece was used as an anode and electrolyzed at 30 ° C. at a current density of ² A / dm ² for 30 seconds. Peeled off. A similar stripping test was performed after leaving the stripping solution for 2 weeks. The stripping solution had good stripping performance, and no change in pH or precipitation was observed.

Example 4 The content of sodium citrate adjusted to pH 9.5 using NaOH was 50 g / l, the content of sodium gluconate was 10 g / l, the content of lysine acetate was 30 g / l, and polyethylene glycol ( (Molecular weight: 600) content is 10
g / l of an aqueous solution (stripping solution), the test piece was used as an anode and electrolyzed at 25 ° C. at a current density of 3 A / dm ² for 30 seconds. Only the part could be peeled off. A similar stripping test was performed after leaving the stripping solution for 2 weeks. The stripping solution had good stripping performance, and no change in pH or precipitation was observed.

Example 5 Using an aqueous solution (stripping liquid) having a sodium gluconate content of 80 g / l and a polyethylene glycol (molecular weight: 1000) content of 5 g / l adjusted to pH 8.5 using KOH. 3A at 25 ° C using the test piece as the anode
When electrolysis was performed for 30 seconds at a current density of / dm ² , only the protruding strike silver-plated portion could be peeled off without attacking the copper surface of the material. In addition, a similar peeling test was performed after leaving the peeling solution for 2 weeks, and it has a good peeling performance.
No change in pH or the like was observed.

Comparative Example 1 Using an aqueous solution having a sodium cyanide content of 100 g / l and an EDTA content of 50 g / l, a test piece was used as an anode and electrolyzed at 25 ° C. at a current density of 5 A / dm ² for 30 seconds. However, the protruding strike-silver-plated portion could be peeled off, but the copper surface of the material was etched and the appearance of the silver surface deteriorated.

Comparative Example 2 (Japanese Examined Patent Publication No. 5-87598) Using an aqueous solution having a succinimide content of 50 g / l adjusted to pH 8.5 using NaOH, using a test piece as an anode at 25 ° C. and 5 A When electrolysis was carried out at a current density of / dm ² for 30 seconds, the protruding strike silver-plated portion could be peeled off, but the copper surface of the material was etched. A similar peel test was performed after the solution was left for one week.
H needed to be corrected and precipitation occurred.

Comparative Example 3 (Japanese Patent Application Laid-Open No. 2-175825) A test piece was anodicly treated with an aqueous solution having a 2-pyrrolidone-5-carboxylic acid content of 40 g / l adjusted to pH 9.5 using KOH. When electrolysis was performed at 30 ° C. at a current density of 3 A / dm ² for 30 seconds, the protruding strike-silver plated portion could be peeled off, but the material copper surface was etched. A similar peeling test was performed after leaving the solution for 2 weeks, but the pH had to be corrected, and precipitation occurred.

Comparative Example 4 (JP-A-7-243100) Using an aqueous solution containing 70 g / l of 5,5-dimethylhydantoin and adjusted to pH 11.5 using KOH, the test piece was used as an anode for 30 minutes. When electrolysis was performed at a current density of 8 A / dm ² at 20 ° C. for 20 seconds, only the protruding strike silver-plated portion could be peeled off without attacking the material copper surface, but the glossiness of the silver-plated portion was significantly increased, Unevenness occurred.

[Bath Life Test] Using the stripping solution (aqueous solution) used in Examples 1 to 5 and Comparative Examples 2 and 3, a 48 hour electrolysis test was performed. In the stripping solutions of Examples 1 to 5,
All showed stable peeling performance without fluctuation of pH, and no generation of precipitation was observed. In the aqueous solution used in Comparative Example 2, it was necessary to adjust the succinimide concentration and pH every two hours. In the aqueous solution used in Comparative Example 3, the copper material was strongly corroded, and an insoluble precipitate was formed.

From the above results, it can be seen that the use of the stripping agent (stripping solution) of the present invention makes it possible to strip unnecessary portions of the silver plating film without adversely affecting the required surface of silver and the material metal. It has been found that the stripping solution of the invention has stable stripping performance over a long period of time.

Continuation of the front page (72) Inventor Shuichi Yoshikawa 1-10-25 Higashi Higashi, Tsurumi-ku, Osaka-shi, Osaka Inside Okuno Pharmaceutical Co., Ltd.

Claims (8)

[Claims] 1. A silver electrolytic stripping agent containing at least one of an aliphatic organic acid and a salt thereof. 2. The composition according to claim 1, which comprises at least one aliphatic organic acid selected from acetic acid, lactic acid, succinic acid, tartaric acid, malic acid, citric acid, gluconic acid, glycolic acid and alkali metal salts thereof, or a salt thereof. 4. The silver electrolytic stripping agent according to item 1. 3. The silver stripping agent according to claim 1, further comprising a nonionic surfactant as an auxiliary component. 4. A nonionic surfactant having a molecular weight of 2
The silver electrolytic stripping agent according to claim 3, which contains polyethylene glycol of 00 to 20,000. 5. A silver electrolytic stripper comprising an aqueous solution containing the electrolytic stripper according to claim 1. Description: 6. An aliphatic organic acid and a salt thereof having a content of 10%.
The electrolytic stripping solution for silver according to claim 5, wherein the amount is ３００300 g / l. 7. The nonionic surfactant content is 0.1%.
The electrolytic stripping solution for silver according to claim 5 or 6, wherein the amount is from 50 to 50 g / l. 8. The electrolytic stripping solution according to claim 5, wherein the pH of the solution is 4 to 14, and an object to be stripped is immersed in the solution.
A method for electrolytically stripping silver, comprising using the object to be stripped as an anode and electrolyzing in an operation range of a liquid temperature of 10 to 80 ° C. and a current density of 0.5 to 10 A / dm ² .