Electrolysis: processes – compositions used therein – and methods – Electrolytic coating – Coating selected area
Patent
1997-09-30
1999-05-11
Mayekar, Kishor
Electrolysis: processes, compositions used therein, and methods
Electrolytic coating
Coating selected area
205252, 205253, 205254, 106 125, 106 127, C25D5/02;3/56
Patent
active
059024720
DESCRIPTION:
BRIEF SUMMARY
FIELD OF TECHNOLOGY
The present invention relates to aqueous solution for forming a metallic complex, tin-silver alloy plating solution, and a method of plating with to said plating solution.
BACKGROUND OF THE INVENTION
A technology of forming metals into metallic complexies are an essential technology in fields of plating, analyzing, etc. Conventionally, cyanides, ammonia, organic acids, etc. are used as complexing agents. But, there is no complexing agent which is effective for all metals; and it is difficult to treat waste water with cyanides, which are relatively effective among said agents, due to the harmful effect to human bodies. Thus, a complexing agent, which is capable of effectively complexing many metals without damaging human health, is required.
On the other hand, pollution of underground water by lead is a type of environmental pollution, and thus products containing lead are severely restricted, such that tin-lead solder is replaced by lead-free solder. Thus, plating layers coated with tin-lead solder should be replaced by lead-free solder.
Thus, tin-silver alloy is to be employed instead of tin-lead solder alloy, and Matsushita Electric Company has disclosed the use of tin-silver solder paste (see Nikken Sangyo Press, Feb. 1, 1996). A method of forming a tin-silver solder layer by plating is now required. The tin-silver alloy has anti-sulphurizability, so it is employed instead of silver.
The difference of electrodeposition potential between silver and tin is 900 mV or more as standard oxidation-reduction potential. Cyanide, e.g., potassium cyanide, is included in the plating solution so as to codeposite tin and silver when forming the tin-silver alloy layer. With the cyanide, there are many problems, including polluting waste water, safe work, etc., so that a tin-silver plating solution including no cyanides is required.
An object of the present invention is to provide an aqueous solution for forming metallic complexes which do not contain cyanides; a tin-silver alloy plating solution, wherein, the composition can be optionally changed; and a method of plating in said plating solution.
DISCLOSURE OF THE INVENTION
To achieve the above objects, the aqueous solution for forming metallic complex should include at least a pyrophosphoric compound and an iodic compound as a basic composition.
The pyrophosphoric compound may include: pyrophosphate, e.g., potassium pyrophosphate, sodium pyrophosphate; and/or pyrophosphoric acid.
The iodic compound may include: iodide, e.g., potassium iodide, sodium iodide; iodite, e.g., potassium iodite, sodium iodite; and/or iodine.
The tin-silver alloy plating solution comprises at least a tin compound, a silver compound, and a complexing agent including a pyrophosphoric compound and an iodic compound as a basic composition.
In the plating solution too, the pyrophosphoric compound may include: pyrophosphate, e.g., potassium pyrophosphate, sodium pyrophosphate; and/or pyrophosphoric acid.
The iodic compound, too, may include: iodide, e.g., potassium iodide, sodium iodide; iodite, e.g., potassium iodite, sodium iodite; and/or iodine.
The a tin compound may be tin compound of an inorganic acid or a tin compound of an organic acid, which is selected from following tin compounds: tin chloride; tin sulfate; tin pyrophosphate; tin iodide; stannic acid; potassium stannate; tin acetate; tin methanesulfonate; tin alkanolsulfonate; and tin phenolsulfonate.
The silver compound may be a silver compound of an inorganic acid or a silver compound of an organic acid, which is selected from following silver compounds: silver iodide; silver chloride; silver nitrate; silver sulfate; silver pyrophosphate; silver iodate; silver acetate; silver methanesulfonate; silver alkanolsulfonate; and silver phenolsulfonate.
The amount of the pyrophosphoric compound and the iodic compound is provided to maintain tin and silver, as complex ions, in the plating solution.
The method of electrolytic plating as defined by the present invention is characterized by plating a work in a plating s
REFERENCES:
patent: 4072605 (1978-02-01), Thelander
patent: 5225096 (1993-07-01), Ahmed et al.
patent: 5711866 (1998-01-01), Lashmore et al.
Arai Susumu
Higashi Mitsutoshi
Watanabe Tohru
Mayekar Kishor
Naganoken and Shinko Electric Industries Co., Ltd.
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