Electrolysis: processes – compositions used therein – and methods – Electrolytic coating – Depositing predominantly alloy coating
Patent
1997-11-04
1999-09-07
Mayekar, Kishor
Electrolysis: processes, compositions used therein, and methods
Electrolytic coating
Depositing predominantly alloy coating
205241, 106 125, 106 127, C25D 330
Patent
active
059482354
DESCRIPTION:
BRIEF SUMMARY
FIELD OF TECHNOLOGY
The present invention relates to plating solution, in which tin-silver-system alloy having lower melting point is made, and a method of plating in said plating solution.
BACKGROUND OF THE INVENTION
Pollution of underground water by lead has been taken as an environmental pollution these days, and products including lead are severely restricted, so that tin-lead solder is replaced by lead-free solder. Thus, plating layers coated with the tin-lead solder should be replaced by the lead-free solder.
Tin-silver-system alloy will be employed instead of the tin-lead solder alloy, so Matsushita Electric Company disclosed tin-silver solder paste (see Nikkei Sangyo Press, Feb. 1, 1996). A method of forming the tin-silver solder layer is required now. But difference of electrodeposition potential between silver and tin is 900 mV or more as standard oxidation-reduction potential, the cyanide, e.g., potassium cyanide, is included in plating solution so as to codeposite tin and silver when forming the tin-silver alloy layer. With the cyanide, there are many problems of polluting waste water, safe work, etc., so the tin-silver plating solution including no cyanides is required.
On the other hand, alloys which are made by adding bismuth, copper, etc. to the tin-silver alloys have better soldering characteristics, so the tin-silver-system alloy plating solution has been required.
An object of the present invention is to provide the tin-silver-system alloy plating solution, which is capable of being employed instead of the tin-lead alloy plating solution, including no cyanides.
DISCLOSURE OF THE INVENTION
To achieve the object, the tin-silver-system alloy plating solution of the present invention comprises following five fundamental ingredients (a)-(e): compounds and copper compounds;
In the tin-silver-system alloy plating solution, the pyrophosphoric compound may include pyrophosphate and/or pyrophosphoric acid.
In the tin-silver-system alloy plating solution, the iodic compound may include iodide, iodite and/or iodine.
In the tin-silver-system alloy plating solution, the tin compound may include a tin compound of inorganic acid or a tin compound of organic acid.
In the tin-silver-system alloy plating solution, the silver compound may include a silver compound of inorganic acid or a silver compound of organic acid.
In the tin-silver-system alloy plating solution, the bismuth compound may include a bismuth compound of inorganic acid or a bismuth compound of organic acid.
In the tin-silver-system alloy plating solution, the copper compound may include a copper compound of inorganic acid or a copper compound of organic acid.
In the tin-silver-system alloy plating solution, prescribed amount of the pyrophosphoric compound and the iodic compound may be included so as to exist tin, silver, bismuth and copper, as complex ions, in the plating solution.
Next, the method of electrolytic plating of the present invention is characterized in that plating solution is tin-silver-system alloy plating solution comprising following five fundamental ingredients (a)-(e): compounds and copper compounds;
Further, the method of plating of the present invention comprises the steps of: forming a resin layer on a surface of a work; forming the resin layer into a prescribed pattern as a plating mask; and executing electrolytic plating on the surface of the work in tin-silver-system alloy plating solution comprising following five fundamental ingredients (a)-(e): compounds and copper compounds;
In this method, the resin layer may be a layer of photosensitive resin, and the photosensitive resin layer may be formed into the prescribed pattern by a manner of photo-lithograph.
In the methods, the pyrophosphoric compound may include pyrophosphate and/or pyrophosphoric acid.
In the methods, the iodic compound may include iodide, iodite and/or iodine.
In the methods, the tin compound may include a tin compound of inorganic acid or a tin compound of organic acid.
In the methods, the silver compound may include a silver compound of
REFERENCES:
patent: 5674374 (1997-10-01), Sakurai et al.
patent: 5711866 (1998-01-01), Lashmore et al.
patent: 5759381 (1998-06-01), Sakurai et al.
Mayekar Kishor
Naganoken
Shinko Electric Industries Co. Ltd.
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