Interconnection of opposite sides of a circuit board

Abstract

A circuit board comprising a dielectric composite (20,22,24) clad with electrical circuitry (16,38) is provided with an improved electrical interconnection between alternate conductive circuitry planes of the substrate. Connecting features (18,40) integral with the conductive circuitry on each conductive plane of the substrate extend into a through hole (30) of the substrate toward each other and are fused (46) to one another by irradiation from a laser beam. In another embodiment a connecting feature (52) from only one of the circuit layers (50) extends into the through hole (66) of the dielectric (60,62,64) and is electrically connected and physically bonded to the circuitry layer on the other side of the substrate by means of fusion or a drop (68) of electrically conductive resin interposed between the raised connector feature and the opposed circuit layer (74). The resin is applied and semi-cured to a 'B'-stage, and then the conductive circuit layers and dielectric are laminated together under heat and pressure to form the substrate. The resin flows into the dielectric hole and over and around the connective feature and thereby providing contact with the circuitry layer of the opposing side. Thereafter the resin is cured to form a strong mechanical and electrical contact.