JPH08337900A - Electrolytically stripping agent for silver - Google Patents

Abstract

PURPOSE: To obtain a stripping agent, which is stable and has long service life in the preservation and the use after producing a bath of the stripping agent, and to provide a stripping method. CONSTITUTION: The 1st stripping agent contains allantoin and NaOH or KOH and the 2nd stripping agent further contains sodium borate or potassium borate. The unnecessary silver plated film on a material to be treated is electrolytically stripped by dipping the silver plated material to be treated in the solution of the stripping agent and using the material to be treated as an anode.

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 and a method for electrolytic stripping which are stable under use and storage conditions and have a long liquid life.

[0002]

2. Description of the Related Art In lead frames used for electronic parts such as ICs, LEDs and transistors, silver is often partially plated on pads for mounting semiconductor chips and leads for wire bonding. When performing the partial plating, a masking process is performed on the non-plating portion. The plating solution often enters the masked portion, and a silver-plated film is often formed on the non-plated portion. Therefore, it is necessary to remove this unnecessary silver plating film after plating. The unnecessary silver plating film is often peeled and removed by electrolysis. It is known that an alkaline stripping solution containing a cyanide compound is used for stripping the silver plating film on the iron-nickel alloy. Further, for stripping a silver plating film on copper or a copper alloy, an electrolytic stripping solution containing no succinimide and / or phthalic acid imide and an alkali metal hydroxide as a main component, which does not contain cyan, has been disclosed. Kaihei 2-104
699).

[0003]

However, these conventional techniques have problems. An alkaline stripping solution containing a cyanide compound used for stripping a silver-plated film on an iron-nickel alloy has a drawback that the appearance of the silver-plated film in a necessary portion is easily changed after electrolytic stripping. In an electrolytic stripping solution containing succinimide and / or phthalimide and an alkali metal hydroxide as main components, the succinimide and / or phthalimide is unstable in an aqueous solution and easily hydrolyzed. Therefore, the life of the liquid is extremely short and the peeling effect does not last long. Further, when the pH is 8 or less, the copper surface is easily dissolved, and there is a drawback that the pH must be controlled within a narrow range of 8 to 9.5. The present invention has been made to solve the above-mentioned problems of the prior art, and an object of the present invention is to provide a stripping agent and a stripping method which are stable and have a long life during storage and use of the stripping solution after it is prepared.

[0004]

As a result of intensive studies to solve the above problems, the present inventor has found that the object of the present invention can be achieved by using allantoin as the main component of the release agent. The present invention relates to an electrolytic stripping agent for silver containing allantoin (5-ureidohydantoin), and a method for electrolytically stripping silver using the electrolytic stripping agent. The release agent of the present invention contains allantoin as a main component, and contains potassium hydroxide as a conductive agent or a pH adjusting agent, or an alkali metal or alkaline earth metal hydroxide such as sodium hydroxide. is there. The stripping agent of the present invention may further contain an alkali metal borate such as potassium borate or sodium borate as a pH buffer in addition to the above components. Allantoin, which is the main component of the present invention, is difficult to hydrolyze when dissolved in water, and thus the pH of the solution does not fluctuate little. This is the reason why it is stable and has a long life as a stripping solution both during use and during storage.

The content of allantoin is not limited, but preferably 1 to 100 g / l, more preferably 50 to 7
5 g / l. Examples of the alkali metal or alkaline earth metal hydroxide added as the conductive agent or the pH adjusting agent include potassium hydroxide and sodium hydroxide. This addition amount may be an amount that can be adjusted to a desired pH, but normally 15 to 30 g / l is preferable.
Examples of the alkali metal borate salt added as the pH buffer include potassium borate, sodium borate and the like. The amount added is not particularly limited, but when added, it is preferably 1 to 75 g / l, more preferably 15 to 35 g / l. By adding these buffers, the degree of pH change can be further reduced, and the life of the electrolytic stripping solution can be further extended.

The present invention also provides a peeling method using the above-mentioned peeling agent. In the stripping method of the present invention, the silver-plated object to be treated is immersed in a solution of the above-mentioned stripping agent, and the object to be treated is used as an anode to electrolyze the silver-plated film on unnecessary portions Peel off. The base metal of the silver plating film is not particularly limited, and examples thereof include copper, a copper alloy, iron, and an iron-nickel alloy, but copper or a copper alloy is preferably used. Stainless steel is usually used as the cathode material.

The pH of the solution is preferably alkaline, more specifically pH 9 to 12, and pH 1
0 to 11.5 is more preferable. The liquid temperature is not particularly limited as long as it is a temperature at which electrolytic stripping can be performed, but is usually 20 to 60 ° C.
Is preferable, and more preferably 35 to 55 ° C. The current density is appropriately selected as necessary, but is usually 1 to 1.
0 A / dm ² is preferred. The silver electrolytic stripping method of the present invention does not require any special equipment, and the existing electrolytic stripping equipment can be used as it is. By using the method of the present invention, it is possible to peel off and remove only unnecessary portions of the silver plating film without dissolving the underlying metal. There is no discoloration, change in gloss, roughening, unevenness, etc. on the required portion of the silver plating film.

[0008]

The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to these examples.

Example 1 Allantoin 60 g / l and KOH 25 g / l were dissolved in water to adjust the pH to 10.0. The temperature of this solution is set to 45 ° C., and a silver plating film (thickness of required portion is 5 μm, thickness of unnecessary portion is 0.5 μm) on a copper lead frame is applied with current density
Electrolysis was carried out at A / dm ² for 15 seconds. The unnecessary portion of the silver plating film was removed, and the necessary portion of the silver plating film was free from unevenness and gloss reduction. In addition, there was no change in the appearance of the lead frame. When this solution was continuously used for 1 week, the pH did not decrease and the surface condition after electrolysis was good as described above.

Example 2 Allantoin 60 g / l and NaOH 20 g / l were dissolved in water to adjust the pH to 11.0. The temperature of this solution was set to 45 ° C. and the same sample as in Example 1 was used at a current density of 2 A / dm ²
Electrolyzed for 5 seconds. The results were the same as in Example 1. The results of continuous use for 1 week were also the same as in Example 1.

Example 3 Allantoin 60 g / l, KOH 20 g / l and potassium borate 20 g / l were dissolved in water to adjust the pH to 10.0. The temperature of this solution was set to 55 ° C., and the same sample as in Example 1 was electrolyzed at a current density of 5 A / dm ² for 15 seconds. The results were the same as in Example 1. The results of continuous use for 1 week were also the same as in Example 1.

Example 4 Allantoin 40 g / l, NaOH 15 g / l and sodium borate 20 g / l were dissolved in water to a pH of 11.0.
And The temperature of this solution was set to 40 ° C., and the same sample as in Example 1 was electrolyzed for 20 seconds at a current density of 6 A / dm ² . The results were the same as in Example 1. The results of continuous use for 1 week were also the same as in Example 1.

Comparative Example 1 45 g / l of succinimide and 7 g / l of KOH were dissolved in water to adjust the pH to 8.5. The temperature of this solution was set to 20 ° C., and the same sample as in Example 1 was electrolyzed at a current density of 5 A / dm ² for 20 seconds. Unremoved parts of the silver plating film were not removed. When this solution was used continuously for one day and night,
After electrolysis, discoloration was observed on the surface of the underlying metal (lead frame). When the pH of the solution was measured, it was lowered to 6.

Comparative Example 2 Phthalimide 50 g / l and KOH 20 g / l were dissolved in water to adjust the pH to 11. Using this solution, electrolysis was performed in the same manner as in Comparative Example 1. The results after electrolysis and after continuous use for I day and night were the same as in Comparative Example 1.

[0015]

The stripping agent of the present invention can strip and remove unnecessary portions of the silver plating film and the underlying metal without damaging the portions of the silver plating film and the underlying metal. Since the main component, allantoin, is difficult to hydrolyze in the solution, p of the solution
The fluctuation of H is small and therefore the life of the stripping solution is long.

Claims (3)

[Claims] 1. A silver electrolytic stripping agent containing allantoin. 2. The electrolytic stripping agent for silver according to claim 1, further comprising an alkali metal borate salt. 3. A method of electrolytically stripping an unnecessary silver-plated film on the object to be treated by immersing the object to be treated plated with silver in the solution of the electrolytic remover according to claim 1 or 2.