Electrolysis: processes – compositions used therein – and methods – Electrolytic coating – Depositing predominantly single metal or alloy coating on...
Patent
1997-12-22
2000-03-14
Gorgos, Kathryn
Electrolysis: processes, compositions used therein, and methods
Electrolytic coating
Depositing predominantly single metal or alloy coating on...
205274, C25D 312, C25D 518
Patent
active
060368330
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to an electroplating method of forming platings of nickel, cobalt, nickel alloys or cobalt alloys in an electrodepositing bath of the type: Watt's bath, chloride bath or a combination thereof by employing pulse plating with a periodic reverse pulse. Current density independence is obtained by means of the invention, whereby low internal stresses are always rendered, wherever the measurement thereof is made on a particular member and whichever current density is used.
BACKGROUND ART
The most common electrodepositing baths for nickel electroplating are Watt's baths containing nickel sulfate, nickel chloride and usually boric acid; chloride baths containing nickel chloride and boric acid, and sulfamate baths containing nickel sulfamate, nickel chloride and usually boric acid. The latter baths are used for the more complicated platings and are difficult and comparatively expensive in use.
Corresponding platings of cobalt may be formed in similar baths containing cobalt sulfate and cobalt chloride instead of the corresponding nickel salts. By adding other metal salts platings of nickel or cobalt alloys are obtained.
It is known to employ a pulsating current, confer for instance W. Kleinekathofer et al, Metalloberfl. 9 (1982), page 411-420, where pulse plating is used by alternating between equal periods of a direct current with a current density of 1 to 20 A/dm.sup.2 and non-current periods, the pulse frequency being from 100 to 500 Hz. By employing a pulsating current and as result of the individual current impulses, an increased formation of crystal nucleuses is obtained, thus rendering a more fine-grained and hard plating.
It is furthermore known to employ pulse plating with periodic reverse pulse, i.e. alternating between a cathodic and anodic current. In the cathodic current cycle, the desired plating formation is obtained by metal deposition, while a portion of the deposited nickel is removed by dissolution in the anodic current cycle, any nodules in the plating thus being smoothed. In order to ensure that the, result is a build-up and not a dissolution of the plating, it is appreciated that the anodic load is to be less than the cathodic load. This method is e.g. described by Sun et al., Metal Finishing, May, 1979, page 33-38, whereby the highest degree of hardness in the plating is obtained at a ratio between the cathodic and the anodic current density of 1:1 with cathodic cycles T.sub.K of 60 msec. alternating with anodic cycles T.sub.A of 20 msec.
U.S. Pat. No. 2,470,775 (Jernstedt et al.) discloses a process for electroplating nickel, cobalt and alloys thereof in an electrodepositing bath containing chlorides and sulfates of the metals. The plating is effected by means of reversed pulse resulting in an improved appearance (smoothness and maximum brightness) as well as in an expedited deposition. An anodic current density is employed of substantially the same range as the cathodic current density. Various additives are mentioned in the U.S. patent, including naphthalene-1,5-disulfonic acid. These additives are referred to as advantageous components, however no directions are rendered in connection with these additives or elsewhere in the patent as to how the mechanical internal stresses are reduced in the platings resulting from electroplating.
EP patent No. 0.079.642 (Veco Beheer B.V.) relates to pulse plating with nickel in an electrolytic bath of the Watt's bath type comprising butynediol or ethylene cyanohydrin as brightener. The deposition is preferably performed at a pulsating current without anodic cycles, but it is stated that anodic cycles, i.e. reverse pulse, can also be employed with the same result. It is, however, not possible to use long anodic pulses in a pure Watt's bath without passivating the nickel layer, whereby any further deposition is prevented. Moreover, said patent discloses that the frequencies used are in a range from 100 to 10,000 Hz.
None of the above mentioned publications relate to internal stresses in platings. U.S. Pat.
REFERENCES:
patent: 2470775 (1949-05-01), Jernstedt et al.
patent: 3437568 (1969-04-01), Hasselmann et al.
F. A. Lowenheim, Electroplating, McGraw-Hill Book Co., New York, pp. 218-219 and 343-345, 1978 (month not available).
G. W. Jernstedt, Better Deposits at Greater Speeds by P R Plating, Plating, Jul. 1948.
Plating With Pulsed and Periodic-Reverse Current, Tai-Ping Sun, et al., Metal Finishing, May, (1979), pp. 33-38.
W. Kleinekathoefer, et al. Metalloberfl. 9 (1982), pp. 411-420, month of publication not available.
Dalby, p. 16 Materialefordeling Ved Galvanoformgiving, publication date not available.
Watson, pp. 3-6 Compendium on nickel electroplating and Electroforming, publication date not available.
INCO, Nickel Electroforming, pp. 22-23, publication date not available.
Dylmer Henrik
M.o slashed.ller Per
Tang Peter Torben
Gorgos Kathryn
Leader William T.
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