JP2997186B2 - Silver electrolytic stripping agent and electrolytic stripping method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a silver electrolytic peeling agent and a silver electrolytic peeling method, and more particularly to a silver electrolytic peeling agent and a silver electrolytic peeling agent suitable for electrolytically peeling unnecessary portions of a silver plating film. The present invention relates to a method for electrolytically stripping silver.

[0002]

2. Description of the Related Art Silver plating is often performed on electronic components such as semiconductor lead frames and connector pins. At this time, a process such as masking is performed on the portion not requiring silver plating, but the silver plating film may protrude into the unnecessary portion in some cases. In such a case, it is necessary to peel off the protruding silver plating film. As a method of peeling an unnecessary portion of the silver plating film, an electrolytic peeling method is known. The electrolytic stripping method is a method in which a silver-plated object to be treated is immersed in a bath of a stripping agent (stripping solution), and the object is used as an anode to electrolyze the silver-plated film. .

[0003] Conventionally, silver electrolytic stripping agents containing concentrated sulfuric acid to which sodium nitrate has been added, those containing a cyanide compound, those containing sodium thiosulfate as a main component, and the like have been used. And copper alloys) to etch the required portion of silver and to use a highly toxic cyanide compound, which requires attention to handling.

[0004] Therefore, as a stripping agent which does not use dangerous concentrated sulfuric acid or highly toxic cyanide, a stripping agent containing succinimide or phthalic imide and an alkali metal hydroxide as main components (Japanese Patent Laid-Open No. 2-104699 (Japanese Patent Publication No. 5-875
98)) and cyclic acid imides containing one nitrogen atom in the molecule, such as those containing 2-pyrrolidone-5-carboxylic acid and those further containing saccharides in addition thereto (JP-A-6-41800). A release agent containing as a main component has been developed.

[0005]

However, a stripping agent comprising a compound containing a cyclic acid imide containing one nitrogen atom in the molecule as a main component is liable to be hydrolyzed by an alkali, and the decomposed product is not easily removed from the bath. Accumulation in the inside has a problem in that passivation, discoloration, unevenness, etc. of the silver plating surface have an adverse effect on a required portion of the silver plating surface, a large amount of main components are consumed, and the life of the bath is short. In addition, when peeling is performed under conditions of high current density, there is a problem that the surface of the silver plating is likely to be passivated or uneven.

Accordingly, an object of the present invention is to develop a silver electrolytic stripping agent and a method of electrolytic stripping, which hardly cause hydrolysis of the main component, have a long bath life, and can strip silver at a high current density. Aimed at.

[0007]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies to solve the above-mentioned problems, and as a result, have found that-
A ring constituent atom include NH- group Ri carbon or nitrogen der,
And piperazine, piperidine, pyrrolidine, imidazo
It has been found that an electrolytic stripping agent containing a nitrogen-containing heterocyclic compound selected from lysine and pyrazolidine as a main component does not easily undergo hydrolysis, has a long bath life, and can be stripped at a high current density. The present invention has been made based on this finding,

[0008]

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[0009] wherein in the ring a group represented by the constituent atoms of the ring Ri carbon or nitrogen der, and piperazine, piperidyl
, Pyrrolidine, imidazolidine and pyrazolidine?
The present invention provides a silver electrolytic stripping agent comprising, as a main component, one or more nitrogen-containing heterocyclic compounds selected from the above or a derivative thereof.

The silver electrolytic stripping agent of the present invention comprises piperazine,
One or more selected from piperidine, pyrrolidine, imidazolidine and pyrazolidine or derivatives thereof as a main component. Further, it is preferable to contain 5-200 g / l of these release agent components as main components. If desired, the silver electrolytic stripper of the present invention may further include a pH buffer and / or a surfactant.

The present invention also provides a method for electrolytically stripping silver, comprising immersing the object to be treated whose surface is silver-plated in the above-mentioned bath of electrolytic stripping agent, and electrolyzing the object using the object as an anode. provide. Electrolytic peeling was performed by using a release agent having a pH of 7 to 14, a bath current density of 0.1 to 20 A / dm ² and a bath temperature of 10 to 10.
It is preferable to carry out the stirring under the condition of 60 ° C.

[0012]

According to the present invention, the main component of the release agent is -N in the ring.
A nitrogen-containing heterocyclic compound containing a H-group and having a ring-constituting atom of carbon or nitrogen. Hydrolysis hardly occurs due to the ring structure. Therefore, it is considered that the bath life is prolonged and peeling at a high current density becomes possible.

[0013]

DETAILED DESCRIPTION OF THE INVENTION The main component of the silver electrolytic release agent of the present invention is

[0014]

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[0015] wherein in the ring a group represented by the constituent atoms of the ring Ri carbon or nitrogen der, and piperazine, piperidyl
, Pyrrolidine, imidazolidine and pyrazolidine?
Or a derivative thereof selected from the group consisting of nitrogen-containing heterocyclic compounds and derivatives thereof .

The concentration range of these main components in the bath is 5 to 5.
It is 200 g / l, preferably 15 to 100 g / l.
If the concentration is too low, passivation of silver is likely to occur, while if the concentration is too high, pumping of the release agent (stripping solution) becomes a problem, which is not preferable.

If necessary, a boric acid compound such as borate or tetraborate is added as a pH buffer.
The concentration range of the pH buffer is 5 to 100 g / l, preferably 10 to 50 g / l. If the concentration is too low, the pH buffering property is low, while if the concentration is too high, the effect is saturated, which is not preferable.

Further, a surfactant is added as required. As the surfactant, any of anionic, cationic and nonionic surfactants or a mixture thereof can be used. The concentration range of the surfactant is 0.
1 to 10000 mg / l, preferably 1 to 1000 mg
/ L. If the concentration is too low, there is no surface active effect, while if the concentration is too high, the effect is saturated, which is not preferable.

Using the above-mentioned stripping agent, silver is electroly stripped under predetermined conditions. The release agent is adjusted with a pH adjuster such as an alkali metal hydroxide such as sodium hydroxide or an alkaline earth metal hydroxide so that the pH is 7-14, preferably 7-12. If the pH is too low, the peeling speed is slow, the silver surface tends to be uneven, and the selective peelability is poor. On the other hand, there is no merit if the pH is too high.

In the present invention, the object to be treated is silver plating or silver brazing on various metal base materials such as iron, nickel alloys such as copper, copper alloy and 42 alloy, stainless steel and nickel alloy. The film on which the film is formed is the object to be peeled.

The object having the silver film formed on the surface is immersed in a bath of an electrolytic stripping agent adjusted as described above, and the object is electrolyzed using the object as an anode. The material of the cathode is not particularly limited, but stainless steel is generally used. The current density was set at 0.
1 to 20 A / dm ² , preferably 0.5 to 10 A / dm ^{2
Assume 2} . If the current density is too low, the peeling rate is low, while if the current density is too high, passivation of silver tends to occur, which is not preferable. In the present invention, 3 to 10 A / dm
Electrolytic delamination at high current density in ² is possible. The electrolysis is performed at a bath temperature of 10 to 60C, preferably 15 to 40C. If the temperature of the bath is too low, the stripping rate is low, while if it is too high, the bath becomes unstable, which is not preferable. It is desirable to stir the bath during the electrolysis, and especially when the current density is high, the stirring speed is preferably high in order not to cause passivation.

When a part of the silver plating film of the object to be processed is peeled off by a release agent bath, a necessary portion of the silver plating film which should not be peeled off is masked or only the portion to be peeled is locally immersed. A method can be adopted. If the silver plating film in the necessary portion is sufficiently thick and may be peeled off to the same extent as the unnecessary portion to be peeled off, the whole may be immersed. When the lead frame is to be processed, the silver plating film of a necessary portion such as a pad portion usually has a low current density portion during electrolytic stripping, and the silver plating film of an unnecessary portion around the portion has a high current portion. Therefore, even if electrolytic peeling is performed without masking the required portion of the silver plating portion, only the unnecessary portion of the silver plating film can be removed.

[0023]

The present invention will be described in more detail with reference to the following Examples and Comparative Examples. (Example) Example No. 1 in Table 1. Release agent baths having the compositions shown in 1 to 5 were prepared. The structural formula of the main component of the release agent bath used in the examples is shown as Chemical Formula 4 for reference.

[0024]

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A lead portion made of copper and having a pad portion subjected to a partial silver plating with a thickness of 5 μm (an unnecessary portion around the pad portion is also provided with a silver plating film).
Was used as a sample and immersed in each of the above release agent baths.
The electrolytic peeling was performed under the peeling conditions shown in (1). That is, pH:
7 to 12, current density: 5.0 A / dm ² , bath temperature: 25
Electrolysis was performed at a temperature of 1.0 ° C., a stirring speed of 1.0 m / sec, and a time of 30 seconds to peel off unnecessary silver. The silver surface appearance and the material appearance of the sample after peeling were observed with a microscope (× 10
0). At the same time, the peeled silver film thickness was measured by X-ray fluorescence. In addition, the same electrolytic stripping was performed 42 days after the bathing of the stripping agent, and a bath life test was performed.

[Results] Both the silver surface appearance and the material appearance were good. The silver release film thickness showed a sufficient release performance of 1.4 to 1.5 μm. The same results were obtained in the test 42 days after the bathing. This indicates that the bath life has not yet been reached.

(Comparative Example) Comparative Example No. A release agent bath containing succinimide as a main component as shown in No. 1 was prepared. A sample obtained by subjecting a pad portion of a lead frame made of copper to partial silver plating with a thickness of 5 μm in the same manner as in the example was immersed in the above-mentioned release agent bath, and subjected to electrolysis under the release conditions shown in Table 1. Peeling was performed. That is, pH: 9, current density: 3.0 A / dm
^2. Bath temperature: 25 ° C, stirring speed: 1.0 m / sec, time: 3
Electrolysis was performed at 0 seconds, and unnecessary silver was peeled off. The sample after peeling was evaluated for the silver surface appearance and the material appearance by microscopic observation (× 100). At the same time, the peeled silver film thickness was measured by X-ray fluorescence. In addition, after the bathing of the release agent, 42
After a day, the same electrolytic peeling was performed, and a bath life test was performed.

[Results] In the initial test of the bath, both the silver surface appearance and the material appearance were good. The silver release film thickness was 0.8 μm. In the test 42 days after the bathing, both the silver surface appearance and the material appearance were uneven and poor. The silver peeling film thickness is 0.4
μm, which was remarkably reduced, indicating that the bath life had already passed.

[0029]

[Table 1]

[0030]

According to the present invention, the life of the silver electrolytic stripping agent can be greatly extended as compared with the conventional one. Further, silver can be peeled at a high current density.

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int. Cl. ⁷ , DB name) C25F 5/00

Claims (5)

(57) [Claims] [Claim 1] The group represented by the include in the ring constituent atoms of the ring Ri carbon or nitrogen der, and piperazine, piperidine, pyrrolidine
A nitrogen-containing heterocyclic compound selected from pyridine, imidazolidine and pyrazolidine , or one of their derivatives or
A silver electrolytic stripping agent characterized by containing more than that as a main component. 2. The silver stripping agent according to claim 1, wherein the silver-containing cyclic compound or a derivative thereof is contained in an amount of 5 to 200 g / l as a main component. Wherein, further comprising a pH buffering agent, and (or) a surfactant, any of claims 1-2 1
Item 7. The electrolytic stripping agent for silver according to item 1. 4. An object to be treated whose surface is silver-plated is immersed in a bath of the electrolytic stripping agent according to any one of claims 1 to 3 , and electrolysis is performed using the object as an anode. The method of electrolytic stripping silver. 5. Electrolytic peeling is performed by using a release agent having a pH of 7 to 14, a bath current density of 0.1 to 20 A / dm ² and a bath temperature of 10 to 10.
The silver electrolytic stripping method according to claim 4 , wherein the method is performed under stirring at 60 ° C.