JPH04160173A - Discoloration preventive liquid for copper - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a discoloration prevention solution for copper.

[Background of the invention]

Recently, high-speed partial plating is often performed when silver plating materials for electronic components such as lead frames.

This high-speed selective silver plating is usually performed as follows.

First, after degreasing and pickling the base material used for electronic component materials such as lead frames, copper strike plating or copper or copper alloy plating treatment (hereinafter referred to in this specification) is performed as necessary to improve adhesion to the base material. In this book, these are collectively referred to as copper strike plating, etc.). Next, the base material that has been subjected to copper strike plating treatment, etc. is washed with water, then pretreated to prevent silver displacement precipitation when the base material is immersed in a silver plating solution, and then subjected to high-speed electrolytic silver plating. conduct.

However, in this silver plating, due to various reasons,
Silver is often plated or deposited on portions of the base material that do not require silver plating. If such abnormal silver precipitation areas are left untreated, silver migration may occur, reducing the reliability of electronic component materials.

Therefore, such abnormal silver deposits are usually selectively dissolved and removed using a known silver stripping solution.

However, when electronic component materials such as lead frames manufactured in this manner are being transported or stored, the treated surfaces that have been subjected to copper strike plating, etc., especially the areas where the materials are overlapped, may become discolored. In recent years, it has come to be recognized that there is a problem.

There is currently no clear conclusion as to the cause of this discoloration, but it has been confirmed that copper oxide is generated in the discolored area. It is thought that the copper surface is oxidized for reasons such as the surface being active or (2) a potential difference occurring between silver and copper, making the copper surface active.

This oxidation discoloration of the copper surface is becoming a major problem as it reduces the reliability of electronic component materials due to the following reasons: - Poor solderability, - Oxidized copper peels off, and there is a risk of short circuits. .

[Means for solving problems]

In order to solve the above-mentioned problems, the inventors of the present invention have conducted intensive studies on the anti-discoloration effect, water wettability, etc. of various additives. It has been discovered that oxidative discoloration of copper can be prevented by immersing the substrate after silver removal in a treatment solution that dissolves and exhibits acidity.

Accordingly, an object of the present invention is to provide a copper discoloration preventing solution that prevents oxidation discoloration of copper in electronic component materials such as silver-plated lead frames and improves the reliability of electronic component materials.

[Structure of the Invention] That is, the present invention provides the following: (1) Silver plating is applied to the surface of copper or a copper alloy or a metal material plated with copper or copper alloy, and the silver adhering to unnecessary parts of the silver plating is peeled off. After that, in the treatment solution for preventing discoloration of copper on the silver peeled surface, S-methyl IH-benzotriazole, 5,
Discoloration of copper characterized by containing one or more selected from 6-dimethyl/IH-benzotriazole and 2-mercaptopyrimidine, and containing an inorganic acid and/or an organic acid to exhibit acidity. Prevention liquid.

(2) The copper discoloration preventing solution as described in (1) above, wherein the copper discoloration preventing solution contains a pH buffering agent.

I will provide a.

[Detailed description of the invention]

Next, in order to facilitate understanding of the present invention, the present invention will be specifically explained in detail.

First, the base materials used in the present invention are mainly electronic component materials such as lead frames, and these are usually made from silver such as copper, copper alloys, iron, iron alloys, nickel, nickel alloys, and those plated with these materials. consisting of any base metal.

These are usually degreased, pickled, and then subjected to copper strike plating treatment, etc., if necessary. This treatment is performed to obtain a silver film that has good adhesion to the base material, and can be omitted if the base material is copper, copper alloy, or a material plated with these and has good plating adhesion.

Conditions for the copper strike plating treatment and the like may be those known in the art and may be selected as appropriate depending on the purpose.

In the present invention, "copper or copper alloy, or a base material in which a metal material is plated with copper or copper alloy" refers not only to copper and copper alloys, but also to copper, copper alloys, iron, iron alloys, nickel, nickel alloys, etc. This includes all metals baser than silver that have been subjected to copper strike plating, etc. Naturally, the copper strike plating treatment and the like may be performed multiple times as necessary.

Next, the base material subjected to the copper strike plating treatment, etc. is washed with water and then immersed in a usual silver plating pretreatment solution (silver displacement prevention solution). The reason for this is that the high-speed silver plating solution has a high silver concentration, and when a substrate made of a metal less base than silver is immersed, a large amount of silver is precipitated by displacement, and this displacement-precipitated silver layer has poor adhesion to the substrate. The adhesion is extremely poor, and even if silver is electroplated on top of this, the adhesion will not be improved, resulting in peeling of the plating film, blistering and discoloration when heated, and if necessary, the silver plating will fail. In addition to extremely poor adhesion of the layer to the base material, parts of the base material that do not need to be plated are also coated with silver, resulting in the loss of expensive silver. This is because there are problems such as contamination by ions of base metals such as copper eluted by substitution reactions.

- The pre-treatment solution for silver plating contains such a silver conversion prevention agent and prevents silver displacement precipitation by forming a thin displacement prevention film on the surface of the substrate. There are no limitations, and examples include thiocarboxylic acids or salts thereof (see JP-A-60-190589), nitrogen-containing heterocyclic compounds such as 2,2'-dipyridyl (see JP-A-60-190591)
and compounds containing a thioureylene group in the ring such as 2-thiobarbic acid (see Japanese Patent Publication No. 1-32318).

The pretreated base material is then immersed in a silver plating solution and plated by electroplating. Note that if the substitutional precipitation inhibitor is added to the silver plating solution, the pretreatment can naturally be omitted.

The silver plating solution is a high-speed silver plating solution in which the concentration of silver contained in the form of alkali silver cyanide is 10 to 1 oOg/Q, and the concentration of free cyanide is 10 g/fi or less.

Potassium silver cyanide is the best alkali silver cyanide, and it also improves the electrical type and conductivity of the liquid and lowers the pH to 7.5.
As salts having a buffering effect within the range of ~9.0, alkali metal salts of phosphoric acid, birophosphoric acid, citric acid and boric acid are contained.

Through the above treatments, silver plating is applied to the base material,
For various reasons, silver is often plated or deposited on parts of the base material that do not require silver plating.

As mentioned above, if such abnormal silver precipitation areas are left untreated, silver migration may occur, reducing the reliability of electronic component materials. It is selectively dissolved and removed using a known silver stripping solution.

After this silver is released from the gOTJ, the base material is immersed in a copper discoloration preventing solution, which is the main focus of the present invention, to prevent copper discoloration and improve the reliability of electronic component materials.

As mentioned above, the copper discoloration preventing liquid of the present invention contains 5-methyl-H-benzotriazole, 5-methyl-benzotriazole,
, 6-dimethyl, H-benzotriazole, and 2-mercaptopyrimidine, and an important characteristic is that it contains an inorganic acid and/or an organic acid and exhibits acidity. .

In the copper discoloration preventing liquid of the present invention, the reason why the liquid is acidic is that the discoloration preventing agent is selected from 5-methyl IH-benzotriazole, 5,6-dimethyl H-benzotriazole, and 2-mercaptopyrimidine. Type 1 or 2
Although the reason is unknown when more than 100% of copper is selected, if it is made alkaline, the discoloration prevention effect of copper is halved, making it practically unusable.

Therefore, acidic in the present invention means a pH range of 7 or less, preferably pH 1-6, more preferably 3-5. If the pH is less than 1, the treated surface subjected to copper strike plating or the like may be eroded, which is not preferable.

The acid that makes the pH of the anti-discoloration liquid acidic may be either an inorganic acid or an organic acid, or a mixture of these may be used.

Examples of inorganic acids include sulfuric acid, nitric acid, hydrochloric acid, phosphoric acid, etc., and examples of organic acids include citric acid, sulfamic acid, acetic acid,
Examples include tartaric acid, but are not particularly limited to these.

However, phosphoric acid or citric acid is particularly preferred, taking into consideration the effect on the base material and the plating surface.

On the other hand, the amount of the discoloration inhibitor added is not particularly limited as long as it is less than the solubility in the acid, but it is not economical to increase the concentration too high considering the possibility of liquid being taken out. Therefore, the amount added is generally 5 to 200 μ/cm due to the discoloration prevention effect.
Q level is considered to be sufficient, but in some cases 1~Lo
It may be added in an amount of approximately g/Q, and may be selected appropriately taking into consideration the processing conditions.

In addition, when such a discoloration prevention liquid is used continuously for a long period of time, it is preferable to add a known pH buffering agent in order to minimize pH fluctuations during use.

The copper discoloration prevention liquid of the present invention adsorbs a very small amount of the discoloration inhibitor component on the surface of the base material and prevents discoloration of copper by its action. After washing the base material with water, preferably immediately
All you need to do is soak it for a second.

Hereinafter, the present invention will be specifically explained with reference to Examples.

[Example] 25mmX40mmXO9 with copper strike plating
After washing a 2 mm' copper alloy base material with pure water, it was washed with 100 μ/Q of 2-thiobarbic acid, which is a substitution inhibitor, and the pH was 10.
KAg(CN), : 130
g/ff, K, HPO4: Contains 100g/Q, p
Immerse it in a high-speed silver plating solution whose H is adjusted to 8.5,
Silver plating was performed for 10 seconds at Dk=70A/dm''.

Then, after washing with pure water, remove the central part (7 mm x 6 mm) and dissolve it using a known silver stripping solution, and after washing with pure water,
Various additives were immersed for 10 seconds in anti-discoloration liquids containing 100 μ/Q and having different pHs.

The base material treated as described in 2 was heat treated by immersing it in boiling pure water for 5 minutes, and the discoloration of the copper strike plating area (silver peeled area) was visually determined. (This is usually done as an accelerated test in cases where the Note that KOH and phosphoric acid were used as pH adjusters.

The results are shown in Table 1.

Margin below Table 1 Group: Discoloration prevention effect O: Effective (no discoloration).

△: Slightly effective (partially discolored).

×: Almost entire surface discolored without any effect).

As is clear from Table 1, when 5-methyl IH-benzotriazole, 5,6-dimethyl-H-benzotriazole and 2-mercaptopyrimidine are used as discoloration inhibitors and in acidic (pH = 4) It can be seen that only copper has an effect of preventing discoloration of copper.

[Effect of the invention] As explained above, the copper discoloration prevention liquid according to the present invention has the following effects:
High-speed silver plating is applied to base materials made of metals less base than silver, such as copper, copper alloys, nickel, nickel alloys, and those plated with these materials, and silver adhering to areas that do not require silver plating is dissolved and removed using a stripping agent. By dipping the base material afterwards, discoloration of the copper can be prevented.

Therefore, the copper discoloration prevention liquid of the present invention has the advantage of being effectively used when manufacturing electronic component materials such as lead frames that undergo high-speed silver plating, since it can improve the reliability of electronic component materials. There is.

Claims (2)

[Claims] (1) Silver plating is applied to the surface of copper or copper alloy or a metal material plated with copper or copper alloy, and after removing the silver adhering to unnecessary parts of the silver plating, discoloration of the copper on the surface from which the silver has been removed In the treatment solution for preventing copper discoloration, 5-methyl IH-benzotriazole, 5,
Discoloration of copper characterized by containing one or more selected from 6-dimethyl/IH-benzotriazole and 2-mercaptopyrimidine, and containing an inorganic acid and/or an organic acid to exhibit acidity. Prevention liquid. (2) The copper discoloration preventing solution according to claim 1, wherein the copper discoloration preventing solution contains a pH buffering agent.