Fabrication of highly conductive stressed-metal springs and their use as sliding-contact interconnects

Stressed-metal springs with small dimensions and high compliance have been demonstrated as alternative to wire bonds and flip-chip solder bumps. For higher spring conductivity and increased wear resistance, additional spring coatings are highly desired. Therefore, we have developed plating procedures which allow us to coat springs with thick and uniform metal films. This paper presents springs plated with gold, copper and nickel and demonstrates assembled spring packages which show low resistance in thermocycling experiments. Furthermore, we present first spring packages on FR4 substrates. Plated stressed-metal springs have a high potential as interconnects in future microelectronics devices where mismatches in thermal expansion between substrates of different materials are becoming an important issue.