Military and commercial hybrids, using high speed integrated circuits with increased input/output density, require low cost, high reliability thick film circuits providing high density, multilayered interconnections with controllable electrical and mechanical characteristics. To meet these criteria it was necessary to adapt the silk screen printing process, including design, materials and reproduction processes, to cater for ‘thick film’, that is able to reproduce extremely fine lines without sacrificing the edge definition of the circuit layout. Printing screens were developed to deposit gold and silver pastes with line/space widths of 50 microns (0.002 in.) on bare ceramic and 100 microns (0.004 in.) on dielectric layers. Interconnection between layers was achieved with 150 micron (0.006 in.) dielectric via openings with corresponding via‐fill conductive connections (gold or silver). The development of the photo‐image onto the emulsion of the screen was deemed to be the most important single step in determining the final print definition of the circuit's design. The main body of this work was concentrated on this approach. The selection of the screens, emulsion system, UV exposure and development processes are also discussed. A capability circuit (CQC) was produced, consisting of five metal layers with line/spaces of 100 microns connected on each side of the ceramic by front to back lasered ‘through‐hole’ connections of 125 microns (0.005 in.) and layer interconnections through 150 micron (0.006 in.) dielectric vias. This capability circuit is classed as an Electronic Component of Assessed Quality by Capability Approval in accordance with BS 63200.
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