JPH11107000A - Electrolytically removing agent for silver - Google Patents

Abstract

PROBLEM TO BE SOLVED: To efficiently peel silver in an unnecessary part without giving bad influences on other part by incorporating hydantoins and at least one kind of component selected from pyridines and cyclic polyamine compds. SOLUTION: This electrolytically removing agent for silver contains one or more component selected from pyridines (such as pyridine) and cyclic polyamine compds (such as hexamethylene tetraimine) and contains hydantoins (such as hydantoin). The removing agent is prepared to contain 1 to 300 g/l pyridines, 1 to 100 g/l cyclic amine compds., 10 to 200 g/l hydantonis and have pH of 6 to 14. The objective product for peeling is dipped as an anode in this liquid and electrolyzed under conditions of a liquid temp. of 10 to 80 deg.C and anode current density of 0.3 to 15 A/dm<2> to peel silver in an unnecessary part. In this method, the removing agent may contain at least one kind as a supplement component of org. acids, aminocarboxylic acids and nonionic surfactant.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

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

[0002]

2. Description of the Related Art In general, in an electronic component such as a lead frame, a silver plating film is formed on a semiconductor chip mounting portion (so-called pad portion), a lead end portion for performing wire bonding, and the like. When silver plating is performed on such a portion, usually, unnecessary portions are masked and silver is plated only on necessary portions. In some cases, the silver plating film protrudes and is formed in portions other than the necessary portions, which may cause a reduction in the reliability of the electronic component.

In such a case, it is necessary to peel off the unnecessary portion of the silver plating film. Usually, it is necessary to immerse the object to be peeled in a stripping solution and perform anodic electrolysis to peel off the unnecessary portion of the plating film. Is being done.

[0004] As a silver electrolytic stripping solution used for such a purpose, a stripping solution containing a cyanide compound such as sodium cyanide or potassium cyanide has been known for a long time. However, cyanide is highly toxic, and causes problems in the treatment of wastewater, the management of chemicals, the safety management during work, and the like. In addition, the stripping solution containing a cyanide has other problems such as corrosion of the base metal and excessive etching of a required silver-plated portion.

In recent years, several non-cyan type strippers have been reported, but each has its own problems. For example,
In Japanese Patent Publication No. 5-87598, a stripping solution containing succinimide and / or phthalic imide and an alkali metal hydroxide as main components is reported. However, the stripping solution has the disadvantage that the main component is unstable in an aqueous solution, the applicable pH range is narrow, and its effect is significantly reduced due to hydrolysis or the like, so that the bath life is extremely short.

[0006] Also, Japanese Patent No. 2641279 discloses that
A silver release agent containing one or more compounds selected from barbituric acid, uracil, glutarimide, 2-pyrrolidone, 3-pyrrolidone, 2-pyrrolidone-5-carboxylic acid, or proline is disclosed. In this case, since the complex forming action on the stripped metal is weak, insoluble metal hydroxide is easily generated in the stripping solution. is there.

Further, Japanese Patent No. 2603800 describes a silver electrolytic stripper containing a specific hydantoin compound, and JP-A-8-337900 describes a silver stripper containing allantoin. . However, since these stripping solutions all specifically attack the silver-plated portions, the appearance of the silver film in the necessary portions is likely to be uneven, and depending on the shape of the processed product, the current that can be used is large. There is an adverse effect that the density range is restricted to a narrow range.
Further, the use of a silver electrolytic stripper containing a hydantoin compound also has a drawback that the base metal tends to be roughened when used for a long time.

[0008]

SUMMARY OF THE INVENTION The main object of the present invention is to:
Unnecessary parts of silver can be efficiently electrolytically peeled off without adversely affecting the material metal and the silver film of the necessary parts.
In addition, an object of the present invention is to provide a non-cyanide type silver electrolytic stripping solution having a long bath life and a silver electrolytic stripping method using the stripping solution.

[0009]

Means for Solving the Problems The present inventor has made intensive studies to solve the above-mentioned problems. As a result, by using an aqueous solution containing at least one of pyridines and a cyclic polyamine compound and a hydantoin as an active ingredient as a silver electrolytic stripping solution, it is possible to eliminate unnecessary portions without adversely affecting the material metal and the required silver film. Silver can be efficiently stripped off, and in particular, after stripping unneeded portions of silver, the uniformity of the appearance of the required silver-plated portion becomes very good, and the stability of the active ingredient in the stripping solution is improved. It is found that the bath life is very long because of the high water content. Furthermore, it has been found that by incorporating an organic acid, an aminocarboxylic acid, a nonionic surfactant and the like as an auxiliary component into the stripping solution, better stripping performance is exhibited, and here, the present invention is completed. Reached.

That is, the present invention provides the following silver electrolytic stripping agent, silver electrolytic stripping solution, and silver electrolytic stripping method.

1. A silver electrolytic stripping agent comprising at least one component selected from pyridines and cyclic polyamine compounds and hydantoins.

2. The pyridines are selected from pyridine, pyridyl alcohol, aminopyridine, alkyl (C ₁ -C ₃ ) pyridine, pyridine carboxylic acids, pyridine dicarboxylic acids, pyridine tricarboxylic acids, pyridine tetracarboxylic acids, pyridine sulfonic acids and amide derivatives of pyridine. Item 4. The silver electrolytic release agent according to Item 1, which is at least one component.

3. Item 2. The silver electrolytic stripping agent according to Item 1 or 2, wherein the cyclic polyamine compound is hexamethylenetetramine.

4. Hydantoins are hydantoins, 1
-Methylhydantoin, 1,3-dimethylhydantoin, 5,5-dimethylhydantoin, 1-methylol-
Item 4. The silver electrolytic stripping agent according to any one of Items 1 to 3, which is at least one component selected from 5,5-dimethylhydantoin and allantoin.

[0015] 5. Item 4. The silver electrolytic stripping agent according to any one of Items 1 to 4, further comprising at least one auxiliary component selected from organic acids, aminocarboxylic acids and nonionic surfactants.

6. Item 6. A silver electrolytic stripping solution which is an aqueous solution of the electrolytic stripping agent according to any one of Items 1 to 5.

[7] Item 6. The silver electrolytic stripping solution according to item 6, wherein the compounding amount of the pyridine is 1 to 300 g / l, the compounding amount of the cyclic polyamine compound is 1 to 100 g / l, and the compounding amount of the hydantoin is 10 to 200 g / l. liquid.

[8] It contains at least one auxiliary component selected from organic acids, aminocarboxylic acids and nonionic surfactants, and the compounding range of at least one of organic acids and aminocarboxylic acids is 5-200 g / l, and nonionic surfactants The silver electrolytic stripping solution according to claim 7, wherein the compounding amount range is 0.1 to 50 g / l.

9. The silver electrolytic stripping solution according to any one of Items 6 to 8, the pH of the stripping solution is set to 6 to 14, the object to be stripped is immersed in this, and the solution temperature is 10 to 8 using the object to be stripped as an anode.
A method for electrolytically stripping silver, comprising electrolyzing at 0 ° C. and an anode current density of 0.3 to 15 A / dm ² .

[0020]

BEST MODE FOR CARRYING OUT THE INVENTION Electrolytic stripping agent The silver electrolytic stripping agent of the present invention contains at least one component selected from pyridines and cyclic polyamine compounds and hydantoins as active ingredients. This stripping agent can be effectively used as an electrolytic stripping solution for silver by using an aqueous solution having a predetermined concentration described later.

In the release agent of the present invention, at least one of pyridine and its derivatives can be used as the pyridine, and the pyridine is not particularly limited as long as it has a solubility required for preparing an aqueous solution having a predetermined concentration. Can be used without. Specific examples of such pyridines include pyridine; 2-pyridinemethanol, 3-pyridinemethanol, 4-pyridinemethanol, 2,6-pyridinedimethanol, 2-pyridineethanol, 4-pyridineethanol, 6-methyl-2. Pyridyl alcohols such as -pyridineethanol, 5-ethyl-2-pyridineethanol;
2-aminopyridine, 3-aminopyridine, 4-aminopyridine, 2,3-diaminopyridine, 2,5-diaminopyridine, 2,6-diaminopyridine, 2,3,6-
Aminopyridines such as triaminopyridine; α-picoline, β-picoline, γ-picoline, 2-ethylpyridine, 3-ethylpyridine, 4-ethylpyridine, 2-propylpyridine, 4-propylpyridine, 2,4-lutidine (C ₁ -C ₃ ) pyridines such as pyridine, 2,6-lutidine and 2,4,6-collidine; pyridinecarboxylic acids such as picolinic acid, nicotinic acid and isonicotinic acid; alkali metal salts of these pyridinecarboxylic acids (Sodium salt,
Pyridinecarboxylic acids such as potassium salts); pyridinedicarboxylic acids such as kelidamic acid, quinolinic acid, lutidic acid, isosinchomeronic acid, dipicolinic acid, cinchomeronic acid, and dinicotinic acid; and alkali metal salts (sodium salts) of these pyridinedicarboxylic acids , Potassium salts and the like); pyridine tricarboxylic acids such as 2,3,5-pyridine tricarboxylic acid and 2,3,6-pyridine tricarboxylic acid; alkali metal salts of these pyridine tricarboxylic acids (sodium salt, potassium Pyridinetricarboxylic acids such as salts; pyridinetetracarboxylic acids such as 2,3,4,6-pyridinetetracarboxylic acid; and pyridine tetracarboxylic acids such as alkali metal salts (sodium salts, potassium salts, etc.) of these pyridinetetracarboxylic acids. Carboxylic acids; pyridine-2-s Pyridinesulfonic acids such as sulfonic acid, pyridine-3-sulfonic acid and pyridine-4-sulfonic acid; pyridinesulfonic acids such as alkali metal salts (sodium salt, potassium salt and the like) of these pyridinesulfonic acids; picolinic acid amide, nicotine Amide derivatives of pyridine such as acid amide, isonicotinamide, pyridine-3-sulfonic acid amide; 2-hydroxypyridine, 3-hydroxypyridine, 4-hydroxypyridine, 2,6-
Hydroxypyridines such as dihydroxypyridine; halogenated pyridines such as 2-chloropyridine, 4-chloropyridine and 2,6-dichloropyridine; pyridine aldehydes such as picolinaldehyde, nicotinaldehyde and isonicotinaldehyde. These compounds can be used alone or in combination of two or more.

Among these, pyridine, pyridyl alcohol, aminopyridine, alkyl (C ₁ -C ₃ ) pyridine, pyridine carboxylic acids, pyridine dicarboxylic acids, pyridine tricarboxylic acids, pyridine tetracarboxylic acids, pyridine sulfonic acids, pyridine The amide derivatives of the above are preferred.

As the cyclic polyamine compound, hexamethylenetetramine, melamine and the like can be used, and hexamethylenetetramine is particularly preferred.

As the hydantoins, at least one of hydantoin and a derivative thereof can be used.
The hydantoins are not particularly limited as long as they are soluble in the stripping solution. Is preferred. These compounds can be used alone or in combination of two or more.

The release agent of the present invention can exhibit sufficient release performance by containing at least one component selected from the above-mentioned pyridines and cyclic polyamine compounds and hydantoins as effective components. Among these components, in particular, at least one component selected from pyridines and cyclic polyamine compounds prevents the occurrence of appearance unevenness of the required portion of the silver film when the unnecessary portion of the silver film is peeled off. Therefore, it works particularly effectively, and is also effective in preventing the occurrence of roughening of the base metal when the stripper is used for a long period of time.

The release agent of the present invention may further contain, if necessary, organic acids, aminocarboxylic acids,
A nonionic surfactant or the like can be added.

Among these auxiliary components, organic acids and aminocarboxylic acids are considered to function as conductive salts, auxiliary complex formers, etc., and by mixing them, the bath conductivity of the stripping solution can be improved. As a result, the stability can be maintained, and the decomposition of the bath is suppressed, and the bath life is prolonged.

As the organic acids, those which are soluble in the stripping solution can be used. For example, formic acid, acetic acid, citric acid, tartaric acid, gluconic acid, succinic acid, malic acid, lactic acid,
Aliphatic organic acids such as glycolic acid, alkali metal salts (such as potassium salts and sodium salts), and ammonium salts of these aliphatic organic acids can be used.

The aminocarboxylic acids can be used as long as they are soluble in the stripping solution. Glycine, glycylglycine, glycylglycylglycine, glycylalanine, alanine, aminobutyric acid, aminocaproic acid, valine, leucine Aliphatic aminocarboxylic acids having an aliphatic chain having about 1 to 10 carbon atoms, such as isoleucine, serine, threonine, cysteine, cystine, methionine, aspartic acid, glutamic acid, lysine and arginine, and alkalis of these aliphatic aminocarboxylic acids Metal salts (such as potassium salts and sodium salts), hydrochlorides, sulfates, acetates and the like can be suitably used.

Any nonionic surfactant can be used without particular limitation as long as it is soluble in the stripping solution. For example, polyethylene glycol having a molecular weight of about 200 to 20,000 can be suitably used. By incorporating a nonionic surfactant, the deterioration of the material metal surface is further suppressed, and it becomes possible to peel off only silver, and when the peeled metal is collected in the cathode, it floats in the bath. Can be suppressed.

In the release agent of the present invention, the organic acids, aminocarboxylic acids and nonionic surfactants, which are the aforementioned auxiliary components, are appropriately selected according to the purpose.
One kind may be blended, or two or more kinds may be used in combination.

Preferred examples of the release agent containing the auxiliary component are shown below.

(1) A release agent containing at least one of pyridines and cyclic polyamine compounds, hydantoins, and at least one of organic acids and aminocarboxylic acids. (2) At least one of pyridines and cyclic polyamine compounds, hydantoins, and Release agent containing nonionic surfactant (3) Release agent containing at least one of pyridines and cyclic polyamine compounds, at least one of hydantoins, organic acids and aminocarboxylic acids, and release agent containing nonionic surfactant Is adjusted to a predetermined pH range when each component is dissolved in water to form an electrolytic stripping solution, and sodium hydroxide and potassium hydroxide necessary for adjusting the pH value of the stripping solution to a predetermined range are used. And the like may be previously blended in the release agent.

The release agent of the present invention may be a mixture in which the above-mentioned components are previously blended so as to have a required mixing ratio, or may be used when preparing an electrolytic release solution without mixing the components. Each component may be separately dissolved so as to obtain an aqueous solution having a predetermined concentration.

Electrolytic Stripping Solution The electrolytic stripping solution of the present invention is an aqueous solution of the above-described electrolytic stripping agent. That is, the electrolytic stripping solution of the present invention, as an active ingredient,
It contains at least one component selected from pyridines and cyclic polyamine compounds, and hydantoins,
An aqueous solution containing, as necessary, organic acids, aminocarboxylic acids, nonionic surfactants, and the like as auxiliary components.

In the electrolytic stripping solution of the present invention, the amount of the pyridine compound is about 1 to 300 g / l, preferably 10 to 15 g / l.
It may be about 0 g / l. The amount of the cyclic polyamine compound is about 1 to 100 g / l, preferably 5 to 5 g / l.
It may be about 0 g / l. At least one of the pyridines and the cyclic polyamine compound may be used, and when both are used at the same time, they can be used within the above-mentioned ranges.

The amount of the hydantoins is from 10 to 200.
g / l, preferably about 20-100 g / l.

If the amount of each of the above components is less than the predetermined range, the bath conductivity is insufficient, and a sufficient peeling effect cannot be obtained. And the amount of water pumped out of the processing liquid also increases, which is uneconomical. Furthermore, when the amount of at least one component selected from pyridines and cyclic polyamine compounds is insufficient, the effect of preventing the appearance unevenness of the required portion of the silver film from being generated cannot be sufficiently exhibited.

In the stripping solution of the present invention, organic acids and aminocarboxylic acids which can be blended as auxiliary components have a similar function.
By adding about 200 g / l, the effect of adding these components is favorably exhibited.

When the amount of the nonionic surfactant added is about 0.1 to 50 g / l, the effect of the addition is favorably exhibited.

In the electrolytic stripping solution of the present invention, the auxiliary component comprising the above-mentioned organic acids, aminocarboxylic acids and nonionic surfactants may be used, if necessary, with any one auxiliary component or two or more auxiliary components. May be added within the above-mentioned range.

The electrolytic stripping solution of the present invention has a pH range of 6-1.
It is preferable to use it after adjusting it to about 4, preferably about 8 to 13. The pH can be adjusted, if necessary, using an alkali metal hydroxide such as sodium hydroxide or potassium hydroxide. When the pH is lower than the above range, the material metal is easily etched, and stable peeling performance may not be obtained, which is not preferable.

Electrolytic stripping method In the present invention, the above-mentioned electrolytic stripping solution is used to immerse an object to be stripped in the stripping solution and to perform electrolysis using this as an anode, thereby efficiently stripping silver on the base metal. Can be. The electrolytic stripping method of the present invention is particularly effective for selectively stripping silver plating applied to unnecessary portions when copper or a copper alloy is used as a base metal and silver plating is performed thereon.

In the electrolytic stripping method of the present invention, the pH of the electrolytic stripping solution is about 6 to 14, preferably about 8 to 13. The temperature of the stripping solution can be in a wide range of about 10 to 80 ° C, but is preferably about 15 to 40 ° C.

The anode current density at the time of peeling is not particularly limited, and can be generally in a wide range of about 0.3 to 15 A / dm ^2. However, if the current density is too low, the time required for peeling becomes longer. On the other hand, if the current density is too high, the material metal is etched, and unevenness or the like occurs in the treated appearance, which is not preferable. Normally, stainless steel or the like can be used as the cathode.

[0046]

According to the present invention, the following remarkable effects can be obtained.

(1) Since the electrolytic stripping solution of the present invention does not contain a harmful cyanide compound, it is highly safe and easy to handle.

(2) The unnecessary portion of the silver film can be peeled off without adversely affecting the material metal and the required portion of the silver plating portion. Particularly, the occurrence of unevenness in the appearance of the required silver-plated portion is prevented, and the uniformity of the appearance becomes very good.

(3) Since the silver film can be peeled off under a wide range of operating conditions, bath management is easy.

(4) Since the stability of the active ingredient in the stripping solution is high, the stripping solution has a long life.

[0051]

The present invention will be described in more detail with reference to the following examples.

In the following Examples and Comparative Examples, a test piece was a 3 × 5 cm copper plate (material) having a polished surface.
A sample in which a 1.1 × 1.1 cm partial silver strike plating was performed and a 1 × 1 cm silver plating film was formed thereon to have a thickness of 5 μm was used. Stainless steel was used as the cathode.

Example 1 10 g / l picoline, 50 g / l pyridine-3-sulfonic acid, and 1-methylol-
Using an aqueous solution (stripping solution) containing 5,5-dimethylhydantoin 50 g / l and adjusted to pH 9.5 using potassium hydroxide, using a test piece as an anode at 20 ° C. and 5 A /
Electrolysis was performed at a current density of dm ² for 30 seconds. As a result, only the protruding silver strike plated portion could be peeled off without invading the material surface of the test piece. No uneven appearance was observed on the silver plating surface.

Further, the same test was carried out after leaving the above-mentioned stripping solution for 4 weeks. However, good stripping performance was exhibited, and no fluctuation of pH, precipitation and the like were observed.

Example 2 Contains 100 g / l of nicotinic acid and 40 g / l of 5,5-dimethylhydantoin
Using an aqueous solution (stripping solution) adjusted to pH 11.5 using potassium hydroxide, using a test piece as an anode at 30 ° C. and 8A
/ Dm ^{2 at} a current density of 20 seconds. As a result, only the protruding silver strike plated portion could be peeled off without invading the material surface of the test piece. No uneven appearance was observed on the silver plating surface.

Further, the same test was carried out after leaving the above-mentioned stripping solution for 4 weeks. However, good stripping performance was exhibited, and no change in pH and precipitation were observed.

Example 3 3-aminopyridine 50 g /
1, hexamethylenetetramine 20 g / l, and 5,5
Using an aqueous solution (stripping solution) containing 100 g / l of dimethylhydantoin and adjusted to pH 10.0 using sodium hydroxide, using a test piece as an anode at 25 ° C and 2 A /
Electrolysis was performed at a current density of dm ² for 60 seconds. As a result, only the protruding silver strike plated portion could be peeled off without invading the material surface of the test piece. No uneven appearance was observed on the silver plating surface.

Further, the same test was carried out after leaving the above-mentioned stripping solution for 4 weeks. However, good stripping performance was exhibited, and no change in pH, precipitation and the like were observed.

Example 4 Hexamethylenetetramine 5
An aqueous solution (stripping solution) containing 0 g / l and 80 g / l of 1-methylhydantoin and adjusted to pH 12.0 using potassium hydroxide was used.
For 10 seconds at a current density of 10 A / dm ² . As a result, only the protruding silver strike plated portion could be peeled off without invading the material surface of the test piece. In addition, no uneven appearance was observed on the silver plating surface.

Further, the same test was carried out after leaving the above-mentioned stripping solution for 4 weeks. However, good stripping performance was exhibited, and no change in pH and precipitation were observed.

Example 5 picolinic acid 50 g / l, hexamethylenetetramine 30 g / l, 1-methylol-
Using an aqueous solution (stripping solution) containing 5,5-dimethylhydantoin 40 g / l and L-glutamic acid 50 g / l and adjusted to pH 8.5 using sodium hydroxide,
Electrolysis was performed for 10 seconds at 25 ° C. at a current density of 10 A / dm ^{2 using} the test piece as an anode. As a result, only the protruding silver strike plated portion could be peeled off without invading the material surface of the test piece. In addition, no uneven appearance was observed on the silver plating surface.

Further, the same test was carried out after leaving the above-mentioned stripping solution for 4 weeks. However, good stripping performance was exhibited, and no change in pH and precipitation were observed.

Example 6 Nicotinic acid 50 g / l, hydantoin 50 g / l, sodium L-glutamate 50
g / l, potassium acetate 20 g / l, and polyethylene glycol (molecular weight = 1000) 5 g / l, using an aqueous solution (stripping solution) adjusted to pH 12.0 using potassium hydroxide, and applying a test piece to the anode 0.5 at 25 ° C
Electrolysis was performed at a current density of A / dm ² for 90 seconds. As a result, only the protruding silver strike plated portion could be peeled off without invading the material surface of the test piece. In addition, no uneven appearance was observed on the silver plating surface.

Further, the same test was carried out after leaving the above-mentioned stripping solution for 4 weeks, but good stripping performance was exhibited, and no fluctuation of pH, precipitation and the like were observed.

Comparative Example 1 100 g of sodium cyanide
/ L and an aqueous solution (stripping solution) containing 50 g / l of EDTA (disodium salt) and a test piece as an anode,
Electrolysis was performed at a current density of 5 A / dm ² at 30 ° C. for 30 seconds. As a result, the protruding silver strike plating was able to be peeled off, but the material surface of the test piece was etched,
The appearance of the silver surface also deteriorated.

Comparative Example 2 An aqueous solution (stripping solution) containing 50 g / l of succinimide and adjusted to pH 8.5 using potassium hydroxide was used, and a test piece was used as an anode at 25 ° C.
At a current density of 5 A / dm ² for 30 seconds. As a result, the protruding silver strike plated portion could be peeled off. However, when this peeling solution was left for one week, a similar test was performed. It was necessary to correct the pH, and the surface of the material was etched. A decrease in peeling performance was observed.

(Comparative Example 3) It contains 40 g / l of 2-pyrrolidone-5-carboxylic acid.
Using an aqueous solution (stripping solution) adjusted to H8.5, electrolysis was performed at 30 ° C. at a current density of 5 A / dm ² for 30 seconds using a test piece as an anode. As a result, the protruding silver strike plated portion could be peeled off, but the material surface of the test piece was etched.

After leaving the above-mentioned stripping solution for one week, a similar test was conducted. It was necessary to correct the pH, and furthermore, the material surface of the test piece was etched, sedimentation occurred, and remarkable stripping performance was observed. A decrease was observed.

(Comparative Example 4) 70 g / l of 5,5-dimethylhydantoin was added, and the pH was adjusted using potassium hydroxide.
Using an aqueous solution (stripping solution) adjusted to 11.5, electrolysis was performed at 40 ° C. and a current density of 8 A / dm ² for 20 seconds using a test piece as an anode. As a result, the protruding silver strike plating part could be peeled off, but the glossiness of the silver plating part increased,
Appearance unevenness occurred.

(Bath Life Test) Using the aqueous solutions (stripping solutions) of Examples 1 to 6 and Comparative Examples 2 and 3, an electrolysis test for 48 hours was performed. Regarding the stripping solutions of Examples 1 to 6, no change in pH was observed, and stable stripping performance was exhibited. Also, no formation of a precipitate was observed.

For the stripping solution of Comparative Example 2, it was necessary to adjust the succinimide concentration and the pH every two hours, and the operation was complicated.

With respect to the stripping solution of Comparative Example 3, the raw material was severely corroded, and an insoluble precipitate was generated.

From the above results, according to the stripping agent (stripping solution) of the present invention, it is possible to strip only the unnecessary portion of the silver plating film without adversely affecting the required silver plating portion and the surface of the base metal. Further, it can be seen that stable peeling performance can be maintained over a long period of time.

Claims (9)

[Claims] 1. A silver electrolytic stripping agent comprising at least one component selected from pyridines and cyclic polyamine compounds, and hydantoins. 2. The method according to claim 1, wherein the pyridines are pyridine, pyridyl alcohol, aminopyridine, alkyl (C ₁ -C ₃ ) pyridine, pyridine carboxylic acids, pyridine dicarboxylic acids,
2. The silver electrolytic stripping agent according to claim 1, which is at least one component selected from pyridine tricarboxylic acids, pyridine tetracarboxylic acids, pyridine sulfonic acids and amide derivatives of pyridine. 3. The silver electrolytic stripping agent according to claim 1, wherein the cyclic polyamine compound is hexamethylenetetramine. 4. The hydantoins are hydantoin, 1-methylhydantoin, 1,3-dimethylhydantoin,
5,5-dimethylhydantoin, 1-methylol-5
The silver electrolytic stripping agent according to any one of claims 1 to 3, which is at least one component selected from 5-dimethylhydantoin and allantoin. 5. The silver electrolytic stripping agent according to claim 1, further comprising at least one auxiliary component selected from organic acids, aminocarboxylic acids and nonionic surfactants. 6. A silver electrolytic stripping solution which is an aqueous solution of the electrolytic stripping agent according to claim 1. 7. The silver electrolytic stripping solution according to claim 6, wherein the amount of the pyridine compound is 1 to 300 g / l, the amount of the cyclic polyamine compound is 1 to 100 g / l, and the amount of the hydantoin compound is 10 to 200 g / l. 1. Silver electrolytic stripper. 8. It contains at least one auxiliary component selected from organic acids, aminocarboxylic acids and nonionic surfactants, and the compounding range of at least one of the organic acids and aminocarboxylic acids is 5-200 g / l. The silver electrolytic stripping solution according to claim 7, wherein the amount of the nonionic surfactant is 0.1 to 50 g / l. 9. The method of claim 6, wherein the pH of the stripping solution is 6 to 14, the stripping object is immersed in the stripping solution, and the stripping object is used as an anode. Warm 10-8
A method for electrolytically stripping silver, comprising electrolyzing at 0 ° C. and an anode current density of 0.3 to 15 A / dm ² .