Chemistry: electrical and wave energy – Apparatus – Electrolytic
Patent
1995-10-06
1998-04-21
Gorgos, Kathryn L.
Chemistry: electrical and wave energy
Apparatus
Electrolytic
C25D 1700
Patent
active
057414076
DESCRIPTION:
BRIEF SUMMARY
This is a national stage application of PCT/FR94/00395 filed Apr. 18, 1994.
BACKGROUND OF THE INVENTION
The present invention relates to a method of manufacturing a silver-plated aluminum conductor, to the resulting silver-plated conductor, and to apparatus for implementing the method.
French patent application 89/10566 describes a method of manufacturing conductor wires made of silver-coated aluminum, the method comprising in succession: degreasing, oxide removal, surface treatment for causing metal seeds to adhere, and depositing a first layer and then a second layer of silver.
However, the efficiency and the speed of that method are not satisfactory. Furthermore, it does not produce silver-plated conductors whose qualities (appearance, adhesion of coating, solderability) are stable, particularly when the aluminum core is of small diameter. Also, manufacturing costs still remain too high and the effluents from the method is toxic and difficult to treat.
SUMMARY OF THE INVENTION
An object of the present invention is to solve the above technical problems by means of a method characterized in that the following steps are performed in succession together with intermediate rinsing steps:
a) the conductor is degreased by being immersed for 3 s to 100 s in a bath maintained at a temperature lying in the range 45.degree. C. to 75.degree. C. and comprising:
b) removing oxide from the conductor by immersion for 2 s to 90 s in a bath at ambient temperature comprising nitric acid at a concentration lying in the range 10% to 60%;
c) treating the surface of the conductor by immersing it for 3 s to 100 s in an adhesion bath maintained at a temperature lying in the range 30.degree. C. to 70.degree. C. and comprising 50 milliliters per liter (ml/l) to 200 ml/l of Ni(BF.sub.4).sub.2 and 10 ml/l to 80 ml/l of Zn(BF.sub.4).sub.2 ;
d) electroplating a first layer of silver by immersion in a first bath at ambient temperature and comprising 50 g/l to 200 g/l of KCN and 1 g/l to 19 g/l of AgCN, using a current density lying in the range 0.1 amps per square decimeter (A/dm.sup.2) to 10 A/dm.sup.2 and anodes made of stainless steel; and
e) electroplating a second layer of silver by immersion in a second bath comprising: using a current density lying in the range 1 A/dm.sup.2 to 10 A/dm.sup.2 and silver anodes.
According to advantageous characteristics, the first layer of silver is obtained by immersion for 6 s at a current density of 3 A/dm.sup.2 in a bath comprising 80 g/l of KCN and 5 g/l of AgCN and the second layer of silver is obtained by immersion for 40 s at a current density of 2.9 A/dm.sup.2 in a bath at 47.degree. C. and comprising:
220 g/l of KCN
115 g/l of AgCN
50 g/l of K.sub.2 CO.sub.3
30 g/l of KOH.
According to other characteristics, degreasing is performed by immersion for 8.5 s in a bath at 60.degree. C. and comprising:
15 g/l of NaOH
10 g/l of Na.sub.2 CO.sub.3
5 g/l of Na.sub.2 SiO.sub.3
15 g/l of NaC.sub.6 H.sub.11 O.sub.7, and oxide removal is performed by immersion for 6 s in a bath of nitric acid at 50%.
Also, the adhesion bath preferably comprises 95 ml/l of Ni(BF.sub.4).sub.2 and 30 ml/l of Zn(BF.sub.4).sub.2 and the surface treatment is performed by immersion for 8.5 s in a bath maintained at 43.degree. C.
The method of the invention makes it possible to multiply manufacturing speed by five compared with prior methods for the same quality of electroplating.
Silver-plated aluminum conductors obtained using prior art methods have poor solderability qualities because of the poor adhesion of the silver coating on the aluminum core. That drawback becomes worse with decreasing core diameter.
The invention therefore also provides a conductor comprising an aluminum-based core coated with at least one layer of silver, characterized in that for a core diameter lying in the range 0.08 mm to 0.5 mm and for a total thickness of silver coating lying in the range 1 .mu.m to 2 .mu.m, the wetting angle lies in the range 25.degree. to 42.degree..
The solderability of a conductor wire is expressed by its suitability
REFERENCES:
patent: 2266330 (1941-12-01), Nachtman
patent: 2392687 (1946-01-01), Nachtman
patent: 2686859 (1954-08-01), Gray et al.
patent: 4886585 (1989-12-01), Martinou et al.
patent: 5245847 (1993-09-01), Bando et al.
Axo'n Cable S.A.
Gorgos Kathryn L.
Wong Edna
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