Stock material or miscellaneous articles – Structurally defined web or sheet – Including aperture
Patent
1990-08-17
1993-03-16
Ryan, Patrick J.
Stock material or miscellaneous articles
Structurally defined web or sheet
Including aperture
428195, 428209, 428409, 428457, 361397, 427 96, 156625, 156654, 156657, 156662, 156668, B32B 310
Patent
active
051943131
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a process for manufacturing through-hole plated single-layer or multi-layer printed circuit boards based on a polymeric substrate material or on ceramics provided optionally on both sides with at least one electroconductive layer by galvanic or electroplating or electroless plating with a metal layer also on those surfaces which have not been coated with a conductive metal layer; the invention further relates to the printed circuit boards themselves.
Through-hole plated printed circuit boards so far have been essentially produced by chemical metal deposition on catalytically activated surfaces of a substrate material. Multi-layer printed circuit boards are also prepared in this manner. The metal layers having been deposited without external current (electroless) are then further reinforced, if desired, by metal-electroplating (galvanic metal deposition). This technology enables high-quality printed circuit boards to be manufactured. The catalytic activation of the surface is generally effected by means of ionic or non-ionic noble metal-containing catalysts which, more specifically are based on palladium and tin. However, systems containing no noble metals, for example based on copper, may also be used. In some cases, there has also been known the use of catalytically active layers which have been applied by a physical method, for example by vapor deposition.
The methods have been described in the pretinent literature, for example in Hermann, Handbuch der Leiterplattentechnik, Eugen G. Leuze Verlag, Saulgau. The wet-chemical catalysis employed in practice with the use of systems containing noble metals or containing no noble metals generally proceeds by the following route:
The quality of nucleation (catalysis) and, hence, the quality of the final product is very much dependent on the methods of pre-treatment which precede catalysis. This is particularly applicable to the conditioning step wherein, on the one hand, the surfaces are cleaned while, on the other hand, the bore hole walls are prepared for the subsequent catalysis. The preparation is effected by means of particular surfactants which occupy the entire surface and have the marked property of adsorbing the catalyst nuclei. The actual catalyst application is followed by a treatment which is appropriate to the system and either removes interfering by-products from the catalyst treatment or converts the nuclei applied in the catalyst into their catalytically active form. Then the step of electroless metallization is carried out. In general, copper is deposited. Minor deviations from the pre-scribed process parameters in one of the process steps will usually lead to a defective metallization so that in many cases the final product is unusable.
Accordingly, one essential drawback inherent to these catalyst systems is the dependence of the nucleation density on the pre-treatment, the particle size and the after-treatment step. The higher the nucleation density, the better is the initial deposition rate or the denisty of the beginning electroless copper-plating, which is equivalent to a high quality through-hole plating. However, defective spots called "voids" in technical jargon, will tend very easily to occur, which voids will greatly reduce the quality of through-hole plating or even render the printed circuit boards unusable. But even under the optimum conditions a surface having been completely occupied with nuclei cannot be obtained. Moreover, the existing catalyst systems are susceptible to inadvertently imported alien ions. Thereby, the reproducibility of their mode of operation as well as the stability thereof are strongly deteriorated. Another disadvantage of the noble metal-containing catalyst systems is the high price of the metals used.
The technology of prior art employing an electroless metallization, followed by optional reinforcing by way of galvanic metal deposition, although it is being widely used, has some disadvantages which so far had to be put with due to the lack of feasible alternatives. Above all
REFERENCES:
E. M. Engler, IBM Technical Disclosure Bulletin, vol. 22 (1), p. 393 (Jun. 1979).
K. C. Kulbe et al., Journal of Polymer Science: Polymer Science: Polymer Chemistry Edition, vol. 20, pp. 1089-1095 (1982).
Hupe Jurgen
Kronenberg Walter
Blas-Berg-Oberflachentechnik GmbH
Evans Elizabeth
Ryan Patrick J.
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