Advanced full additive process for high density printed wiring boards

A description is given of a recently developed heat-resistant adhesive for the full additive process, which has been used successfully for the formation of excellent anchors without the use of synthetic rubber. An epoxy resin with excellent heat resistance and electrical insulating properties is used instead. The adhesive is prepared from an oxidizing-agent-soluble particulate epoxy resin and a heat-resistant epoxy resin solution, that is substantially insoluble in oxidizing agents. The adhesive is applied to an insulating substrate and cured to form an adhesive layer. The particulate epoxy resin on the surface of the cured layer is dissolved by an oxidizing agent to form fine anchors, whereby firm bonding between the unclad laminate and the conductor circuit can be achieved. Full-additive wiring boards made with this heat-resistant adhesive characteristically show high accuracy in high-density wiring, high electrical reliability, high bonding strength at high temperatures, and excellent soldering heat resistance and wire-bonding properties. It is suitable for making printed wiring boards with high density and high reliability