Electrolysis: processes – compositions used therein – and methods – Electrolytic coating – Depositing predominantly alloy coating
Reexamination Certificate
2001-10-09
2003-04-08
Wong, Edna (Department: 1741)
Electrolysis: processes, compositions used therein, and methods
Electrolytic coating
Depositing predominantly alloy coating
C205S252000, C205S253000, C106S001260
Reexamination Certificate
active
06544398
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a gold-tin alloy plating bath that does not contain cyanide compounds.
2. Description of the Related Art
Of gold-tin alloy plating films, one having a eutectic composition, i.e. an Au:Sn ratio of 80:20 by weight, for example, has a melting point of 280° C., and is widely used as a low-melting-point high-strength brazing material, for example when joining various chip components to semiconductor substrates, or when sealing packages by brazing. Moreover, gold-tin alloy plating films have good corrosion resistance and appearance, and are thus also used in white gold plating for decorative purposes and the like.
Conventionally, so-called cyanide type plating baths in which a cyanide compound is added to stabilize the gold ions are used as gold-tin alloy plating baths. However, cyanide compounds are harmful to the human body, and hence there are large problems in terms of work safety and environmental protection.
There are thus calls for non-cyanide-type gold-tin alloy plating baths that do not contain cyanide compounds. However, the current state of affairs with conventionally used non-cyanide-type gold-tin alloy plating baths is that there are cases in which the electrodeposited film is mat rather than bright deposit, or the electrodeposit is coarse and a film cannot be formed, and hence it is not possible to form a gold alloy film of sufficient commercial value.
SUMMARY OF THE INVENTION
A principal object of the present invention is to provide a non-cyanide-type gold-tin alloy plating bath which is capable of forming a gold-tin alloy plating film that has good brightness, reflow properties and the like.
The inventors of the present invention carried out assiduous studies toward attaining the above object, and as a result arrived at the present invention after discovering that if a cationic macromolecular surfactant or a cationic macromolecular compound is added to a non-cyanide-type gold-tin alloy plating bath containing a water-soluble gold compound, a complexing agent for gold and a water-soluble tin compound, the gold-tin alloy film formed from the plating bath has excellent brightness and good reflow properties.
The present invention thus provides a non-cyanide-type gold-tin alloy plating bath, a gold-tin alloy plating method, and an article having formed thereon a gold-tin alloy plating film, as follows.
1. A non-cyanide-type gold-tin alloy plating bath comprising:
(i) at least one water-soluble gold compound,
(ii) at least one complexing agent for gold,
(iii) at least one water-soluble tin compound, and
(iv) at least one component selected from the group consisting of cationic macromolecular surfactants and cationic macromolecular compounds.
2. The non-cyanide-type gold-tin alloy plating bath according to item 1, wherein the cationic macromolecular surfactant is a quaternary ammonium salt of a diallylamine polymer.
3. The non-cyanide-type gold-tin alloy plating bath according to item 1, wherein a mixture of at least one water-soluble stannous compound and at least one water-soluble stannic compound is used as the water-soluble tin compound.
4. The non-cyanide-type gold-tin alloy plating bath according to item 1, further comprising at least one additive selected from the group consisting of complexing agents for tin, masking agents, oxidation inhibitors, brightening agents, semi-brightening agents, pH regulators, buffering agents and electrically conductive salts.
5. A gold-tin alloy plating method comprising the step of applying an electric current, using an article to be plated as a cathode, in the non-cyanide-type gold-tin alloy plating bath according to any of items 1 through 4.
6. An electronic component having a gold-tin alloy plating film formed thereon using the method according to item 5.
The non-cyanide-type gold-tin alloy plating bath of the present invention contains as essential components (i) at least one water-soluble gold compound, (ii) at least one complexing agent for gold, (iii) at least one water-soluble tin compound, and (iv) at least one component selected from the group consisting of cationic macromolecular surfactants and cationic macromolecular compounds.
Following is a more detailed description of the components contained in the plating bath of the present invention.
(i) Water-soluble Gold Compound
Any water-soluble gold compound other than a cyanide can be used as a water-soluble gold compound in the present invention. Specific examples of water-soluble gold compounds include potassium chloroaurate, sodium chloroaurate, ammonium chloroaurate, gold potassium sulfite, gold sodium sulfite, gold ammonium sulfite, gold potassium thiosulfate, gold sodium thiosulfate and gold ammonium thiosulfate. Either a single water-soluble gold compound may be used, or two or more may be used mixed together.
The water-soluble gold compound concentration in the plating bath is preferably about 0.002 to 20 g per liter, more preferably about 0.5 to 10 g per liter, in terms of the amount of gold.
(ii) Complexing Agent for Gold
Any known complexing agent for gold(I) ion other than a cyanide can be used as a complexing agent for gold in the present invention. Specific examples of such complexing agents include sulfurous acid, and sulfites such as potassium sulfite, sodium sulfite, ammonium sulfite and alkaline earth metal sulfites; thiosulfuric acid, and thiosulfates such as potassium thiosulfate, sodium thiosulfate, ammonium thiosulfate and alkaline earth metal thiosulfates; and pyrophosphoric acid, and pyrophosphates such as potassium pyrophosphate, sodium pyrophosphate, ammonium pyrophosphate and alkaline earth metal pyrophosphates. Either a single gold complexing agent may be used, or two or more may be used mixed together.
The concentration of complexing agent for gold in the plating bath is preferably about 0.01 to 5 mol per liter, more preferably about 0.05 to 3 mol per liter.
(iii) Water-soluble Tin Compound
At least one compound selected from the group consisting of water-soluble stannous compounds and water-soluble stannic compounds can be used as the water-soluble tin compound(s) in the present invention.
Specific examples of the water-soluble stannous compounds include stannous salts of organic sulfonic acids such as methanesulfonic acid, ethanesulfonic acid, 2-propanolsulfonic acid and p-phenolsulfonic acid; stannous borofluoride; stannous sulfosuccinate; stannous chloride; stannous sulfate; and stannous oxide.
Specific examples of the water-soluble stannic compounds include stannic salts of the above-mentioned organic sulfonic acids; salts of metastannic acid such as is sodium metastannate, potassium metastannate; stannic sulfate; stannic chloride; stannic oxide; stannic carbonate; stannic acetate; stannic pyrophosphate; and stannic oxalate.
Either a single water-soluble tin compound may be used, or two or more may be used mixed together. In particular, by using one or more water-soluble stannous compounds and one or more water-soluble stannic compounds in combination, the stability of the gold-tin alloy plating bath can be improved, and the brightness and reflow properties of the plating film formed can also be improved. In this case, there are no particular limitations on the ratio of the water-soluble stannous compound content to the water-soluble stannic compound content, with it being possible, for example, for this ratio to be anywhere in a broad range of about 1:9 to 9:1 (by weight).
The total water-soluble tin compound concentration in the plating bath is preferably about 0.01 to 5 mol per liter, more preferably about 0.05 to 3 mol per liter, in terms of the amount of tin.
(iv) Cationic Macromolecular Surfactants and Cationic Macromolecular Compounds
It is necessarily to add at least one component selected from the group consisting of cationic macromolecular surfactants and cationic macromolecular compounds to the gold-tin alloy plating bath of the present invention. By including such an additive, the plating film formed from the plating bath can be given an excell
Okada Takashi
Uchida Ei
Armstrong Westerman & Hattori, LLP
Ishihara Chemical Co., LTD
Wong Edna
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