High temperature tin-copper joints produced at low process temperature for stress reduction

A fluxless bonding technique using Sn-Cu multilayer composites to produce high temperature joints at relatively low temperature is presented. At a 280 degrees C process temperature, joints which were almost void-free, with a melting point of 415 degrees C, were made. With a further annealing step, re-melting temperature of the joints increases to 713 degrees C. The technique, thus, gives a quantum jump to the post-processing temperature of the components fabricated. As a result of decreased bonding temperature, stresses in the fabricated components are greatly reduced. SEM results clearly show the microstructures of the joints that consist of Cu6Sn5 and Cu3Sn intermetallic phases, thereby verifying the proposed bonding principle. No flux is required because tin oxidation is inhibited in the fabrication processes.