JPH0261073A - Electroless tin plating bath and electroless tin plating method - Google Patents

Abstract

PURPOSE:To develop an electroless tin plating liquid which forms dense tin plating consisting of uniform and fine particles by dissolving specific org. sulfonic acids, the bivalent tin salt thereof, thiourea and water soluble Zr salt in water. CONSTITUTION:The electroless Sn plating liquid consisting of the aq. acidic soln. contg. 20 to 300g/l>=1 kinds of the sulfonic acids selected from substd. or unsubstd. alkane sulfonic acid, hydroxyalkane sulfonic acid, benzene sulfonic acid, and naphthalene sulfonic acid, 10 to 54g/l bivalent Sn salt of these sulfonic acids as Sn ion, 30 to 130g/l thiourea, and 10 to 1000mg/l water soluble zirconium salt such as zirconium nitrate and zirconium acetyl acetate as Zr ions and having 0.5 to 0.9pH is used, by which the dense electroless Sn plating film consisting of the uniform and fine particles is obtd. on the surface of the object to be plated.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to an acidic electroless tin plating bath and an electroless tin plating method.

[Prior art and problems to be solved by the invention] Conventionally, electroless tin plating has been applied to electronic parts etc. from the viewpoint of soldering properties, etc., but in this case, plating of electronic parts etc. is unnecessary. Partial plating is often done by masking the area and plating only the necessary areas. When performing such partial plating, especially when plating electronic components, masking accuracy is strongly required, and various masking agents and masking methods have been developed in response to this, but in general, masking agents are sensitive to alkalinity and If plating is performed in a plating bath, the masking film may peel off, and as the materials used for electronic components become more diverse, the number of materials with poor alkali resistance is increasing, so acidic plating baths are used for such partial plating. type is desired.

Conventionally, chloride baths, sulfuric acid baths, etc. are known as acidic electroless tin plating baths, but the problem is that the tin precipitates obtained from these baths have relatively coarse particles and the precipitation rate is slow. Therefore, an acidic type plating bath that provides an electroless tin plating film with fine and dense particles is required.

Conventionally, a bath using organic sulfonic acids together with trivalent titanium ions has been known as an alkaline electroless tin plating bath (Japanese Patent Publication No. 34229/1983); As mentioned above, the bath is selective plating using a masking agent with weak alkali resistance.
It is difficult to apply to materials with weak alkali resistance.

The present invention has been made in view of the above circumstances, and includes an acidic electroless tin plating bath that provides tin precipitates of uniform and fine particles and has a good deposition rate, and a tin plating bath using the electroless tin plating bath. The purpose is to provide an electrolytic tin plating method.

[Means and effects for solving the problem] The present inventors,
As a result of various studies to achieve the above objective, we have found that one or more organic sulfonic acids selected from substituted or unsubstituted alkanesulfonic acids, hydroxyalkanesulfonic acids, benzenesulfonic acids, and naphthalenesulfonic acids are used as acids, and By using salts of these organic sulfonic acids as divalent tin salts, adding thiourea, and further adding a water-soluble zirconium salt to a bath containing these components, a tin film was precipitated from this bath. The inventors have discovered that the particles are uniform and fine, have a dense precipitation state with good appearance, and have a relatively good precipitation rate, leading to the present invention.

The present invention will be explained in more detail below.

The electroless tin plating bath according to the present invention includes one or more organic sulfonic acids selected from substituted or unsubstituted alkanesulfonic acids, hydroxyalkanesulfonic acids, benzenesulfonic acids, and naphthalenesulfonic acids, and divalent tin plating baths of these sulfonic acids. It contains tin salt, thiourea, and water-soluble zirconyl salt.

Here, as the unsubstituted alkanesulfonic acid, CnH
Those represented by 2n + x S O3H (where n is 1 to 5, preferably 1 or 2) can be used, and unsubstituted hydroxyalkanesulfonic acids include ○H C,l,H,,Y1 -CH-C,H,,+,-5o3H
(However, m is 0 to 2, and Q is 1 to 3) can be used. Further, as substituted alkanesulfonic acids and hydroxyalkanesulfonic acids, those in which a portion of the hydrogen atoms of the alkyl groups are substituted with halogen atoms, aryl groups, alkylaryl groups, carboxyl groups, sulfonic acid groups, etc. can be used. On the other hand, benzenesulfonic acid and naphthalenesulfonic acid are represented by the following formula, and in naphthalenesulfonic acid, some of the hydrogen atoms in the benzene ring and naphthalene ring are hydroxyl groups, halogen atoms, alkyl group, carboxyl group, nitro group.

Those substituted with mercapto groups, amino groups, sulfonic acid groups, etc. can be used.

Specifically, organic carboxylic acids that can be suitably used in the present invention include methanesulfonic acid, ethanesulfonic acid, propanesulfonic acid, 2-propanesulfonic acid, butanesulfonic acid, 2-butanesulfonic acid, pentanesulfonic acid, Chlorpropanesulfonic acid, 2-hydroxyethane-1-
Sulfonic acid, 2-hydroxypropane-1-sulfonic acid, 2-hydroxybutane-1-sulfonic acid, 2-hydroxypentanesulfonic acid, allylsulfonic acid, 2-sulfoacetic acid, 2- or 3-sulfopropionic acid, sulfosuccinic acid acids, sulfomaleic acid, sulfofumaric acid, benzenesulfonic acid, toluenesulfonic acid, xylene sulfonic acid,
Examples include nitrobenzenesulfonic acid, sulfobenzoic acid, sulfosalicylic acid, benzaldehyde sulfonic acid, and p-phenolsulfonic acid, and one or more of these can be used in combination.

The plating bath of the present invention contains the above-mentioned organic sulfonic acids and divalent tin salts of these organic sulfonic acids, and in this case, the types of organic sulfonic acids may be different between the acid and the tin salt. , preferably the same. Note that the divalent tin salt of an organic sulfonic acid is prepared by using an excess of organic sulfonic acid and adding another divalent tin salt to it to form a divalent tin salt of an organic sulfonic acid in a plating bath. You may also do so.

The amount of the organic sulfonic acid used is 2 per 112 plating baths.
It is preferable to set it as 0-30og, especially 50-150g, and it is preferable to set it as 10-50g, especially 10-30g of divalent tin salt as a tin ion. In this case, the ratio of organic sulfonic acid to divalent tin ion is 1 to 10:1,
In particular, a ratio of about 3 to 7:1 is suitable.

The thiourea used in the present invention acts as a complexing agent, and the amount used is 30 to 130 g per plating bath IQ.
Especially preferred is 50 to 110 g.

A water-soluble zirconium salt is further added to the plating bath of the present invention, and by adding the water-soluble zirconium salt, it is possible to form a precipitated film of uniform and fine particles. In this case, zirconium nitrate, zirconium acetylacetonate, etc. can be used as the water-soluble zirconium salt, and the amount used is 10 to 1 zirconium ion.
000 ■/Q, especially 50 to 200 ■/Q is effective. If the amount of zirconium is too small, the effect of making the particles of the electroless tin plating film finer may not be sufficiently exerted, and if it is too large, the precipitation speed may be reduced.

Note that the plating bath of the present invention is acidic, especially at pH 0.2.
-1.5, more preferably 0.5-0.9.

When performing electroless tin plating using the above-mentioned dipping bath, the temperature is preferably 60 to 90°C, particularly 65 to 80"C. In this case, the object to be plated is appropriately selected, such as copper, copper alloy, etc. It is suitably used for electroless tin plating.Additionally, stirring can be performed if necessary during plating.

Next, the present invention will be specifically explained with reference to examples, but the present invention is not limited to the following examples.

〔Example〕

An electroless tin plating bath having the following composition was prepared.

Methanesulfonic acid 100 g/Q thiourea 80 g/Q zirconium nitrate 100 μ/Q pH 0.8 Next, plating was performed at 70° C. using the above plating bath on a copper plate pretreated by a conventional method.

The appearance of the obtained electroless tin plating film was a uniform silvery white color, and when observed under a microscope, the particles were fine and uniform, as shown in Reference Photo 1.

Further, the deposition rate was 0.5 p in 3 minutes and 1.3 p in 30 minutes.

For comparison, plating was performed using a plating bath having the same composition as above except that zirconium nitrate was not added. The obtained electroless tin plating film contained coarse particles as shown in Reference Photo 2.

Note that reference photographs 1 and 2 are both micrographs at a magnification of 40 times.

〔Effect of the invention〕

As explained above, according to the present invention, a dense electroless tin plating film made of uniform fine particles can be formed from an acid bath.

Claims (1)

[Scope of Claims] 1. One or more organic sulfonic acids selected from substituted or unsubstituted alkanesulfonic acids, hydroxyalkanesulfonic acids, benzenesulfonic acids, and naphthalenesulfonic acids;
An electroless tin plating bath characterized by containing a divalent tin salt of these sulfonic acids, thiourea, and a water-soluble zirconium salt. 2. An electroless tin plating method, characterized in that an object to be plated is electrolessly tin plated using the electroless tin plating bath according to claim 1.