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Post Metallization of Via Connection Passages in Prefired Multilayer Ceramic Printed Circuits

IP.com Disclosure Number: IPCOM000077512D
Original Publication Date: 1972-Aug-01
Included in the Prior Art Database: 2005-Feb-25
Document File: 2 page(s) / 47K

Publishing Venue

IBM

Related People

Anderson, LC: AUTHOR

Abstract

Irregular via passages 1 in multilayer ceramic structure 2 (Fig. 1) are required to be metallized with electrically continuous metal deposits. When the activation layer for the deposit is formed on the particulate (green) structure, subsequent drying and firing leaves the deposit in nonuniform conditions of accumulation exemplified in Figs. 2 and 3; resulting in uncertain electrical continuity.

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Post Metallization of Via Connection Passages in Prefired Multilayer Ceramic Printed Circuits

Irregular via passages 1 in multilayer ceramic structure 2 (Fig. 1) are required to be metallized with electrically continuous metal deposits. When the activation layer for the deposit is formed on the particulate (green) structure, subsequent drying and firing leaves the deposit in nonuniform conditions of accumulation exemplified in Figs. 2 and 3; resulting in uncertain electrical continuity.

To avoid this, the activation layer and deposit may be formed after the ceramic has been fired. The activation layer is applied by immersion of the structure in a liquid solution containing a molybdenum salt and a gel forming material. The solution is maintained liquid by heat supplied at a temperature below the firing temperature of the ceramic. Upon cooling, the gel forms and fills the via passages (Fig. 4). A hard vacuum is applied subsequently, overnight or sooner, to remove the water from the gel structure (Fig. 5). The solids of the gel formation are consumed (burned out) by chemical activity, in which the molybdenum salt is reduced to metallic molybdenum forming a continuous activation layer permeating and coating the via surfaces.

Additional metal is deposited on this activation layer by the conventional procedure of dipping the part in molten copper (temperature well below the ceramic firing temperature). Since copper selectively wets only the molybdenum coated surfaces,...