Joining of molybdenum thin films with copper printed circuit board by laser micro-riveting

Abstract

The joining of micron devices by bonding of thin films is required for the electrical or mechanical connection of thin film components. Current developments of flexible electronics call for advanced micron interconnection technologies. For the joining of thin film devices on flexible polymer substrates a novel technique called “laser microriveting” (LMR) is introduced and demonstrated which enables the bonding of two thin metal layers of different materials for mechanical and electrical connections. In this approach the mechanical and electrical connections are achieved by geometrical interlocking of the thin film materials as a consequence of pulsed laser irradiation. Imaging by SEM and EDX shows clearly that a hollow rivet of copper is formed interlocking the copper layer with the overlaying molybdenum film. The copper hollow rivet formation is the result of highly-dynamic laser-driven processes of melting, evaporation, recoil pressure formation, material transport processes, and resolidification of the molten copper within a single laser pulse. A contact resistance of less than 100mΩ for one rivet of approximately 20μm size was measured. This new approach provides a solution for current problems of joining very dissimilar materials.