Plated copper on ceramic for power hybrid applications

A technique for plating copper onto ceramic with top layers of nickel, gold, and/or solder is described. The adhesion mechanism of the copper is an interlocking of the film and ceramic surface to form a mechanical bond. Soldered adhesion of the copper did not degrade during high-temperature storage or thermal cycling. A nickel barrier between the plated copper and solder inhibits diffusion and intermetallic formation. Testing of small-diameter gold and large-diameter aluminum wire bonds after high-temperature storage demonstrated the reliability of wire bonding to the Cu/Ni/Au metallization. While a small percentage of bond lifts occurred among the aluminum-wire-bond samples stored at 200°C, the bond strengths were high and there was no increase in series bond resistance. Preliminary evaluation of a screen-printable polyimide encapsulant revealed pinholes in the cured film. Alternate polyimide formulations are being evaluated. A 2-MHz, 100-W DC-DC converter was fabricated to demonstrate the use of plated copper on ceramic substrate technology