Electrolysis: processes – compositions used therein – and methods – Electrolytic coating – Controlling current distribution within bath
Patent
1996-11-26
1998-09-08
Gorgos, Kathryn L.
Electrolysis: processes, compositions used therein, and methods
Electrolytic coating
Controlling current distribution within bath
204224R, 204268, 204DIG7, 205 97, 205125, 205147, 205640, 205652, 205717, 205721, C25D 502, C25D 522, C25F 700
Patent
active
058040528
DESCRIPTION:
BRIEF SUMMARY
DESCRIPTION
This is a national stage application of PCT/DE95/00706, filed May 26, 1995.
The invention relates to a method and a device in particular for continuous uniform electrolytic metallizing or etching of metal surfaces.
Methods of metallizing or etching, particularly for processing and manufacturing printed circuit boards, and devices suitable for this purpose have been known for a long time. For example there is described in DE 36 24 481 A1 an arrangement for electrolytic application of a metal to plate-shaped articles such as printed circuit boards, in which these articles are brought into an electrolysis bath for a certain residence time and are then removed from the bath, the articles being supplied in a horizontal position to an electrolysis chamber forming the arrangement, being passed continuously through this and after electrolytic treatment are brought out of the chamber again, and in which anodes, power supplies and transport means are provided. The transport means are further in the form of an endlessly revolving driven series of individual transport members, which securely hold the lateral edges of the plate-shaped articles and move them in the direction of travel, and in which at the beginning and end of the transport path situated in the electrolysis chamber, means are provided which cause the articles to be grasped by the transport members or released by them. Such an installation can be used with corresponding additional equipment also for electrolytic etching for example the removal of metal coatings (demetallizing).
In other arrangements, the articles to be treated are dipped in a vertical position into a treatment agent or are brought into contact therewith by spraying or injection, the counter electrodes necessary for the electrolytic treatment being located opposite the said article. For electrolytic metallization, the counter electrodes are polarised as anodes and for an etching process as cathodes.
In the known electrolytic installations in which the articles are disposed horizontally and are moved in a horizontal direction through the arrangement, the spacing between the articles and the counter electrodes comes to approximately 100 mm. In the manufacture of printed circuit boards, such large spacings have a detrimental effect on the quality of the coatings to be processed. Narrow conductor strips on the printed circuit boards act relative to adjacent wide conductor strips as peaks, on which the electrical field in the electrolytic treatment cell is concentrated. Therefore a higher localised current density forms at these points, so that these points are thus more intensively, i.e. more rapidly electrolytically etched or metallized than wide conductor strips.
As a result coating thickness ratios of 1:3 and more are encountered at the various points on the surface of a printed circuit board. During etching, the different electrical field intensities lead to an attack on the lateral flanks of a conductor strip and thus to under-etching. This is no longer tolerable in fine conductor technology, in which conductor strip widths of 0.1 mm and less are to be produced.
In order to solve this problem various measures are possible, individually or in combination. Thus for example the electrolytic treatment may be carried out at a low current density. However, in this way the efficiency of the treatment installation is reduced. Improvements are also achieved with an enlarged spacing between anode and cathode. On the other hand, the peak effect described may also be avoided in that the spacing between anode and cathode is reduced so far that the narrow conductor strips no longer act as peaks, but as surfaces. This is the case particularly when the counter-electrodes (during etching the cathodes, and during metallizing the anodes) are brought closer to the articles for treatment to a spacing of 1 mm or less. In this case the maximum usable current density is limited only by the required quality of the metal coatings to be processed or produced and the thickness-specific surfaces of the d
REFERENCES:
patent: 3619386 (1971-11-01), Eisner
patent: 3699017 (1972-10-01), Eisner
patent: 4043891 (1977-08-01), Alkire
patent: 4776939 (1988-10-01), Blasing et al.
patent: 5024735 (1991-06-01), Kadija
Atotech Deutschland GmbH
Gorgos Kathryn L.
Leader William T.
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