JP2680012B2 - Electroless tin-lead alloy plating bath - Google Patents

Description

TECHNICAL FIELD The present invention relates to an electroless tin-lead alloy plating bath used when electroless tin-lead alloy plating is applied to copper or a copper alloy.

(Conventional Technology and Problems Thereof) Tin plating or tin-lead alloy plating is widely used for electronic parts and the like because it improves solderability. In particular, tin-lead alloy plating does not generate whiskers peculiar to tin plating, and thus is useful for semiconductor device packages and the like that are becoming smaller, more complicated, and have more pins.

Conventionally used baths for electrolytic tin-lead alloy plating are baths using a mineral acid such as a sulfuric acid bath and a hydrochloric acid bath, and a fluoride bath. However, these baths cannot avoid the severe attack of copper or copper alloy materials by mineral acids or fluorides, which causes a problem of damaging the materials. Especially for electronic components such as tape carriers with a copper foil circuit formed on an insulating resin sheet such as polyimide, the lead width is extremely small, about 100 μm, so attack of mineral acid etc. on the root of the lead etc. Is large and susceptible to adverse effects such as disconnection.
Mineral acid is often used mainly because hydrochloric acid is mainly used because the plating appearance is inferior when sulfuric acid is used.However, when the electronic component is a semiconductor device component, chlorine ion is used in terms of product cleanliness. Is preferably not present and a hydrochloric acid bath is also not preferred.

Further, as this type of plating bath, an electroless plating bath that is easy to handle is desired.

Therefore, the present invention has been made to solve the above problems, and an object of the present invention is that tin or copper- or a copper alloy has a gentle attack on the material and has good adhesion.
An object of the present invention is to provide an electroless tin-lead alloy plating bath capable of obtaining a lead alloy plating film and avoiding adverse effects on electronic parts and the like since chlorine ions do not exist.

(Means for Solving Problems) According to the electroless tin-lead alloy plating bath according to the present invention for the above purpose, an organic sulfonic acid selected from alkanesulfonic acid, alkanolsulfonic acid, and aromatic sulfonic acid, It is characterized by containing a divalent tin salt and a lead salt of these organic sulfonic acids, sodium hypophosphite, and thiourea.

Furthermore, according to the present invention, an organic sulfonic acid selected from alkane sulfonic acid, alkanol sulfonic acid, and aromatic sulfonic acid, divalent tin salts and lead salts of these organic sulfonic acids, and sodium hypophosphite, From thiourea and one or more of styrene, cinnamyl alcohol, cinnamic acid, cinnamaldehyde, o-methoxycinnamic acid, 2-furyl aclick acid, benzalacetone, and other α, β-unsaturated ketones or aldehydes. And a second brightener made of one or more of formalin or an imidazoline derivative.

In the present invention, an organic sulfonic acid and its divalent tin salt or lead salt are used without using a mineral acid such as hydrochloric acid or sulfuric acid or a fluoride. Compared to mineral acids and fluorides, organic sulfonic acids
The attack on the material copper or copper alloy is extremely gentle. As the organic sulfonic acid, from alkane sulfonic acid, alkanol sulfonic acid, aromatic sulfonic acid,
Select alone or in combination as appropriate. Further, in the present invention, sodium hypophosphite is contained as a reducing agent for electroless plating, and thiourea is contained as an essential composition as a complexing agent that stably holds copper eluted by substitution in a solution.

The amount of the organic sulfonic acid added is not particularly limited, but a suitable range is 5 g / to 200 g /. Further, tin salt and lead salt of organic sulfonic acid are 5 g / to 200 g /, sodium hypophosphite is 30 g / to 200 g /, and thiourea is 30 g / to 200 g /.

The pH is preferably about 2 to 3, and the bath temperature is preferably about 80 ° C. in relation to the plating rate.

With the above basic bath, a practically effective electroless tin-lead alloy plating film can be obtained.

Other additives include buffers to keep the pH of the bath constant, surfactants to meet the smoothness of the plating film surface, tin and lead deposition, crystallization accelerators and copper elution enhancements. Agents and brighteners are added as needed.

Oxycarboxylic acids such as citric acid, tartaric acid and malic acid are preferable as the above buffer.

Examples of the surfactant include laurylpyridinium chloride as a cationic surfactant, sodium lauryl sulfate as an anionic surfactant, and Triton-X (trade name, manufactured by Wako Pure Chemical Industries, Ltd.) as a nonionic surfactant, Tween (trade name, manufactured by Kao Atlas Co., Ltd.) or the like is suitable,
These are added alone or in combination.

As a promoter of precipitation of tin and lead, crystallization and elution of copper, a general formula, (R is an alkyl group or a benzene nucleus)
Use complexing agents such as A, methyl EDTA and CDTA.

As the brightener, as a first brightener, α, β-unsaturated ketones such as styrene, cinnamyl alcohol, cinnamamic acid, cinnamaldehyde, orthomethoxycinamic acid, 2-furylacrylic acid, and benzalacetone; Or aldehydes alone or in combination,
As the second brightener, a formalin or imidazoline derivative is used alone or in combination. The first brightener and the second brightener are added in combination. Addition of these brighteners makes it possible to obtain an electroless tin-lead alloy plating film having sufficient gloss.

The amount of oxycarboxylic acid added as a buffer is
Although not particularly limited, 5 g / ~ 100 g / is a preferable range, 0.01 ~ 50 g / surfactant, 0.5 ~ 100 g / complexing agent.
The preferred range of the brightener is 0.01 to 50 g /.

In addition, the plating bath according to the present invention has low foamability due to the addition of a surfactant, and since it uses organic tin, organic lead and organic sulfonic acid, it can be used as a conventional sulfuric acid-based, hydrochloric acid-based, or fluoride-based plating bath. Compared with this, it has a low specific gravity and the viscosity of the liquid is low, so it can be easily washed with water in the post-treatment after plating and is also clean. Therefore, the cleanliness of the product is increased.

In addition, in the tin-lead alloy plating for semiconductor parts, chlorine ions do not exist, so the bath is satisfactory in terms of product cleanliness.

 Hereinafter, specific examples will be described.

Example 1 Methanesulfonic acid 50 g / tin methanesulfonate 20 g / lead methanesulfonate 13 g / thiourea 75 g / sodium hypophosphite 80 g / citric acid 15 g / laurylpyridinium chloride 5 g / EDTA 3 g / of the above composition An electroless tin-lead alloy plating bath was constructed.
This bath has a PH of about 2.0. When the bath temperature of this bath was set to about 80 ° C and the tape carrier was immersed for 10 minutes, 1.
A smooth and uniform matte tin-lead alloy plating of 0 μm was obtained. The tin-lead ratio in the film was about the same as the tin-lead ratio in the bath, which was 6: 4. The adhesion of the obtained plating was good, and pinholes were not observed at all even when observed under a microscope. No attack was observed on the material resin part, and the lead base had a good plating appearance.

Example 2 50 g methanesulfonic acid / 20 g tin methanesulfonate / 13 g lead methanesulfonate / 75 g thiourea / 80 g sodium hypophosphite / 15 g citric acid / 5 g laurylpyridinium chloride / 3 g EDTA / Benzalacetone 0.5g / Formalin 1.0g / An electroless tin-lead alloy plating bath having the above composition was constructed.
This bath has a PH of about 2.5. When the bath temperature of this bath was set to about 80 ° C and the tape carrier was immersed for 10 minutes, 1.
A smooth and uniform 6: 4 bright tin-lead alloy plating of 0 μm was obtained. The adhesion of this plating was good, and no pinhole was observed. No attack was observed on the material resin part, and the base of the lead had a good plating appearance.

If methyl EDTA or CDTA is used instead of EDTA,
And cinnamic acid instead of benzalacetone,
A good bright tin-lead alloy plating was also obtained when cinnamaldehyde was used.

In Examples 1 and 2, as the pretreatment of the object to be plated, the usual process of alkali resin → cyan electrolysis → acid dipping is sufficient, and if the object to be plated is uniformly wet with water, it is dried. Even if it was not performed, uneven plating was not caused and a uniform plating appearance was obtained.

In addition, in Examples 1 and 2, methanesulfonic acid and its divalent tin salt, or alkanesulfonic acid and its divalent tin salt, lead salt instead of lead salt, or alkanolsulfonic acid and its divalent tin. Similar results were obtained using salts and lead salts.

Further, even when the above-mentioned surfactant such as sodium lauryl sulfate is used instead of laurylpyridinium chloride in Examples 1 and 2, in Example 2, the above-mentioned styrene such as styrene is used instead of benzalacetone. Even when the first brightening agent was used and an imidazoline derivative was used instead of formalin, bright tin plating excellent in appearance was obtained.

Further, in each of the examples, the post-plating post-treatment washing with water was easily performed.

(Effects of the Invention) As described above, the electroless tin-lead alloy plating bath according to the present invention has the following unique effects.

Since it does not contain mineral acid or fluoride, the attack of the material on copper or copper alloy is gradual, and adverse effects such as corrosion and disconnection of the wiring circuit can be avoided.

It is possible to obtain an electroless tin-lead alloy plating film having a desired thickness that is pinhole-free, uniform, smooth, and has excellent adhesion.

 High plating speed and excellent workability.

Since it does not contain a mineral acid or a fluoride, it is safe in handling, the working atmosphere is not only good, but also it has a low specific gravity and a low viscosity, so that it can be easily washed with water in the post-treatment after plating.

It is an organic sulfonic acid-based plating bath, which is suitable as a plating bath for electronic parts because it has no chlorine ions.

By using the above-described first brightening agent and second brightening agent together, a tin-lead alloy plating film having electroless plating and excellent gloss can be obtained.

As described above, the present invention has been described variously with reference to preferred embodiments, but the present invention is not limited to these embodiments,
Of course, many modifications can be made without departing from the spirit of the invention.

Claims (2)

(57) [Claims] 1. An organic sulfonic acid selected from alkane sulfonic acids, alkanol sulfonic acids and aromatic sulfonic acids, divalent tin salts and lead salts of these organic sulfonic acids, sodium hypophosphite and thiourea. An electroless tin-lead alloy plating bath comprising: 2. An organic sulfonic acid selected from alkane sulfonic acids, alkanol sulfonic acids, and aromatic sulfonic acids, divalent tin salts and lead salts of these organic sulfonic acids, sodium hypophosphite, and thiourea. And styrene,
Cinnamyl alcohol, cinnamic acid, cinnamaldehyde, o-methoxycinnamic acid, 2
-Containing a first brightening agent made of one or more α, β-unsaturated ketones such as furylaclick acid, benzalacetone, or an aldehyde, and a second brightening agent made of one or more formalin or an imidazoline derivative. Characteristic electroless tin-lead alloy plating bath.