Electrolysis: processes – compositions used therein – and methods – Electrolytic coating – Treating process fluid by means other than agitation or...
Patent
1998-04-23
2000-08-08
Gorgos, Kathryn
Electrolysis: processes, compositions used therein, and methods
Electrolytic coating
Treating process fluid by means other than agitation or...
205103, 205104, 205292, 205920, C25D 518, C25D 2118
Patent
active
060997117
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a method for the electrolytic deposition of metal coatings with uniform coating thickness, particularly of copper coatings with certain physical-mechanical and optical characteristics.
BACKGROUND OF THE INVENTION
In order to achieve certain physical-mechanical properties in metal coatings, which can be deposited electrolytically, certain additive compounds must be added in small amounts to the deposition solution. Of main concern in this respect are organic materials, which have an effect on the bright finish, the levelling and the uniformity of the deposition on large surfaces, avoidance of so-called burnt-on particles, i.e. deposition of granular crystalline coatings and also the construction of metal coatings with high fracture elongation and tensile strength.
The disadvantage in this respect is that these materials generally disintegrate during deposition, so that they have to be replenished during the operation. Admittedly, the observation of constant conditions in production is mostly very difficult, since the materials themselves are only present in very small concentrations in the deposition solutions, and in addition a complicated mixture of several materials of this type is also most often required to achieve certain coating properties and finally during dissolution degraded products are formed also, which have an effect on the metal coating properties. Therefore, an analytical survey of the additive compounds is not only very difficult, but is generally not adequate either for completely describing the state of the deposition bath, with the result that analytical methods for controlling the bath may only be used in a qualified manner.
In addition there is a demand, in the coating of complex shaped workpieces for example of circuit boards with very fine borings, for achieving as uniform a thickness of metal coating as possible on all points of the workpiece. It is possible, with appropriate deposition baths with optimised composition, to enlarge the metal coating thickness even in places with a low current density. However, the named additive compounds only influence the metal dispersion so slightly that the problem was not solved by these optimising measures.
In particular, it was not possible with the named measures to achieve even an adequately uniform distribution of metal coating thickness in complex shaped workpieces, for example in circuit boards with very fine borings.
Various means of solving the problem have been suggested therefore in the literature, however none of them have yet led to entirely satisfactory solutions.
As a solution for the equalising of the metal distribution on the surfaces of the workpieces which are to be coated, the use of insoluble anodes during metal deposition is suggested. Anodes of this type are known from the German Patent document DD 215 589 B5 and in the publication DD 261 613 A1. Furthermore methods of this type are also described in DE 43 44 387 A1. In these publications mention is made also of the addition of compounds of electrochemically reversible redox systems to the depositing solution, with which systems the addition of metal salts for completing the deposited metal ions should be avoided.
A periodic current reversal during electrolysis is suggested as a further solution for equalising the coating thickness on the workpieces ("Pulse Plating-Elektrolytische Metallabscheidung mit Pulsstrom", Ed. Jean-Claude Puippe and Frank Leaman, Eugen G. Leuze Verlag, Saulgau, Germany, 1986, p.26 and "Pulse Plating of Copper for Printed Circuit Technology" M. R. Kalantary, D. R. Gabe, Metal finishing 1991 pp. 21 to 27). However, adequate uniformity of the deposited metal coatings cannot be achieved in this way on large and in addition complex shaped workpieces.
Furthermore, in DE 27 39 427 C2 a method for uniform coating of profiled workpieces, which have narrow recesses, is described. For this purpose, the recesses in the surface of the workpiece are treated very intensively with electrolytic solution and, at the same time, an electri
REFERENCES:
patent: 5186811 (1993-02-01), Otani et al.
Pulse Reverse Copper Plating for Printed Circuit Boards, William F. Hall et al, AES 10th Plating in the Electronics Industry Symposium, Feb. 1983.
Pulse Plating of Copper for Printed Circuit Board Technology, by M.R. Kalantary & D.R. Gabe, Loughborough University of Technology, Leicestershire, England, Apr. 1991.
Pulse-Plating-Elektroytische MEtallabscheidung mit Pulsstrom, Ed. Jean-Claude Puippe and Frank Leaman, Eugene G. Leuze Verlag Saulgau, Germany, 1986, Month of Publication Not Available p. 26.
Hartverchromung mittels eines Gleichrichters mit pulsierenden Wellen und periodischer Umkehr der Polaritat by C. Colombini in the Professional Paper Galvanotecknik, 1988, Month of Publication Not Available pp. 2869 to 2871.
George W. Jernstedt, Better Deposits at Greater Speeds by P R Plating, Plating, Jul. 1948.
Dahms Wolfgang
Kretschmer Stefan
Meyer Heinrich
Atotech Deutschland GmbH
Gorgos Kathryn
Leader William T.
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