JPH021240B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a hydrochloric acid acid electrosoldering bath capable of obtaining an electrodeposited surface with a good appearance without forming needle crystals under conditions of high current density and high temperature. Conventionally, acidic baths such as sulfuric acid baths and hofting baths have been the mainstream for soldering baths, and are mainly used for loose plating and barrel plating, while jet plating and flow plating, which pursue high speed, are mostly used. Not done. In other words, high speed requires high temperature and strong stirring, but in the case of the above acidic bath, high temperature and strong stirring are necessary.
This is because under strong stirring, divalent tin ions are oxidized to tetravalent tin ions, forming precipitates and reaching the end of the bath life. Still, although the above-mentioned borofusting bath seems to have achieved a certain degree of high speed, it is not satisfactory, and there are also problems with safety for workers, difficulty in treating fluoride waste water, and corrosion of various materials. There are drawbacks such as strong adhesiveness and difficulty in selecting materials for plating equipment. In view of these drawbacks of conventional soldering baths, the inventors decided to consider a hydrochloric acid bath that is less dangerous to work with and easier to treat as waste water. However, conventional hydrochloric acid acid baths have a rough electrodeposited surface and tend to produce needle-like crystals.
It is difficult to obtain an electrodeposited surface with a good appearance, and the method has not reached the level of industrial practical use. The objects of the present invention are to provide a low operational risk, easy wastewater treatment, and the ability to obtain an electrodeposited surface that is dense and has a good appearance without forming needle crystals, and moreover, to achieve high speed. Our objective is to provide a hydrochloric acid acidic electric soldering bath, and its features include a basic plating solution containing stannous chloride, lead acetate, and hydrochloric acid as main components, as well as an alkylpyridinium salt and an unsaturated carbonyl compound. It is located at the point where the is added. In addition, an alkylpyridinium salt and an unsaturated carbonyl compound are added to a basic plating solution whose main components are stannous chloride, lead acetate, and hydrochloric acid, and then polyethylene glycol alkyl phenyl ether or a polyoxyethylene compound is added. It is characterized by what it did. The basic bath of the present invention contains stannous chloride, lead acetate, and hydrochloric acid as main components. Lead salts include lead chloride, lead monoxide,
Lead dioxide and the like are difficult to use because they are difficult to bathe in dilute hydrochloric acid. As an additive, laurylpyridinium chloride has the effect of suppressing dendrite-like precipitation.
There is a sufficient effect within the range of 5g/. However, when laurylpyridinium chloride is used alone, when performing high-speed flow plating, only a dark and rough electrodeposited surface is obtained, and high speed cannot be achieved. Benzalacetone enables this high-speed flow plating and has a sufficient leveling effect in the range of 0.01 to 0.1 g/. Since benzalacetone itself is insoluble in water, it must be mixed and dissolved in a surfactant such as laurylpyridinium chloride before use. Even by simply adding an alkylpyridinium salt such as laurylpyridinium chloride and an unsaturated carbonyl compound such as benzalacetone or cinnamaldehyde to the above basic bath, no needle crystals can be obtained.
It is possible to obtain electrodeposited surfaces with good appearance. Triton X-100 (trade name): Polyethylene glycol alkyl phenyl ether enables even faster plating. Triton X-100 yellows the liquid due to the addition of laurylpyridinium chloride,
It suppresses the turbidity of the solution due to long-term use, stabilizes the bath, extends the bath life, suppresses the rapid growth of crystals, and acts as a plating speed accelerating agent, as shown in Table 1. The maximum current density range that provides a good electrodeposited surface changes depending on the presence or absence of the electrodeposition. In addition, instead of Triton X-100, Tween 80
(Product name): Similar effects can be obtained when polyoxyethylene sorbita monooleate is used. The amount of Triton X-100 and Tween 80 added is 3
A range of ml/~5ml/ is sufficient.

[Table] Example 1 Stannous chloride 30g / Lead acetate 10g / Hydrochloric acid 0.5N Hydrazine dihydrochloride 4g / Laurylpyridinium chloride 2g / Benzalacetone 0.05g / Triton X-100 3ml / At various current densities of this bath A photograph showing the condition of the plated surface is shown in FIG. Further, FIG. 2 shows photographs showing the state of the plating surface at various current densities in baths having the above composition but not containing Triton X-100. As is clear from Figures 1 and 2, the plating surface of the Triton X-100 additive-free bath is rough and rugged, but the plating surface of the Triton X-100 additive bath is dense and smooth, resulting in good plating. Appearance is obtained. Furthermore, by adding Triton X-100, a good plating appearance can be obtained in a high current density range, and high speeds can be achieved. Table 2 shows the proportions of tin and lead in the solder deposits.

[Table] As is clear from Table 2, the current density is 40A/dm ²
Within the range of ~70 A/dm ² , the proportion of lead in the precipitate becomes almost constant, making it easier to manage plating in field work. Furthermore, by varying the concentrations of tin and lead, the proportion of lead in the precipitate at the same current density can be varied over a wide range from 2% to 70%. Note that hydrazine dihydrochloride has the effect of stabilizing the bath at high temperatures (50°C, 60°C or higher). In other words, at high temperatures, tin is oxidized from divalent to tetravalent, lowering its specific gravity and impairing the adhesion of plating, but hydrazine dihydrochloride acts as a reducing agent to reduce tetravalent tin to divalent. This makes it possible to stabilize the bath. The concentration of hydrazine dihydrochloride is 1-20g/
It is effective within the range of In addition, as a reducing agent,
Hydroquinone, hypophosphorous acid, and other substances that do not have sulfuric acid groups are effective in stabilizing the bath, and these may be used alone or in combination. Example 2 Stannous chloride 30g/Lead acetate 10g/Hydrochloric acid 0.5N Hydroquinone 2g/Laurylpyridinium chloride 2g/Cinnamaldehyde 0.05g/Tween 80 3ml/This example had the same plating speed and plating as Example 1. Appearance obtained. Note that if other metal compounds such as zinc chloride and antimony trioxide are added in place of lead acetate, they can also serve as an alloy bath for each of them. It can also be used as a tin bath if lead acetate is not added. As described above, according to the present invention, a smooth and dense electrodeposited surface can be obtained at high speed even in a hydrochloric acid soldering bath, which conventionally produced only a rough appearance. In particular, in the plating bath of the present invention,
Usage within the high current density range of 40A/dm ² to 70A/dm ² can be achieved, reducing the conventional soldering bath to 5A/dm 2 .
Considering that dm ² to 10 A/dm ² , the plating time can be reduced to less than 1/6. For example, in the plating process of lead frames for semiconductor devices, the solder plating process can be completed in an extremely short time. It has great effects such as being able to be incorporated into the same plating line as the spot silver plating that is carried out. Further, in the present invention, it is possible to use not only high-speed flow plating but also normal bath plating in a higher current density range than conventional ones, and the plating time can be shortened. Although the present invention has been variously explained above with reference to preferred embodiments, the present invention is not limited to these embodiments, and it goes without saying that many modifications can be made without departing from the spirit of the invention. It is.

[Brief explanation of drawings]

Figure 1 is a SEM photograph showing the plating surface condition of the Triton X-100 additive bath, and Figure 2 is the Triton X-100 additive-free bath.

Claims (1)

[Scope of Claims] 1. Hydrochloric acid acid electric soldering characterized by adding an alkylpyridinium salt and an unsaturated carbonyl compound to a basic plating solution containing stannous chloride, lead acetate, and hydrochloric acid as main components. bath. 2. An alkylpyridinium salt and an unsaturated carbonyl compound were added to a basic plating solution containing stannous chloride, lead acetate, and hydrochloric acid as main components, and then polyethylene glycol alkyl phenyl ether or polyoxyethylene compound was added. A hydrochloric acid acidic electric soldering bath characterized by: