GB1329770A - Printed circuits - Google Patents

Abstract

1329770 Printed circuits NL INDUSTRIES Inc 30 Dec 1971 [30 Dec 1970] 60868/71 Heading H1R [Also in Division C4] A process for the manufacture of printed circuit boards comprises applying a desired pattern of conductors on a ceramic substrate with a liquid composition consisting of the reaction product of aluminium powder with an aqueous vehicle which contains the reaction product of a chromate, a phosphate and at least one oxide, hydroxide or carbonate of either an alkaline earth metal (preferably magnesium), iron or aluminium, said liquid composition being dried and fired in an oxidizing atmosphere at a temperature within the range 590‹ C. to 950‹ C. The conductive lines thus produced adhere to the substrate and have low electrical resistance. Small amounts of silver electrical paste are applied at points where soldered connections are required and the body is refired in an oxidizing atmosphere, i.e. air. Alternatively, silver pads may be formed on the substrate before the formation of the conductive lines. In order to improve the printing characteristics of the liquid composition the viscosity and surface tension may be altered by adding ethyl cellulose or some other specified viscosity improver. The aluminium powder used should all be able to pass through a 325 mesh sieve (U.S. standard) and the weight ratio of aluminium powder to the solid ingredients of the vehicle should be from 3À5 : 1 to 5À0 : 1. The allowed proportions of the remaining ingredients are also given.