High temperature silver-indium joints manufactured at low temperature

A fluxless bonding process using indium-silver multilayer composite to produce high temperature joints at relatively low temperature has been developed. The process temperature is 220 degrees C. Joints, which an almost void-free, with melting temperatures of 210 degrees C are first made. After further annealing at 130 degrees C, the re-melting temperature increases to above 750 degrees C. The technique, thus, provides a quantum jump to the post-processing temperature of component fabrication. The joints are examined using a scanning acoustic microscope to confirm the bonding quality. The joint cross-sections are studied using scanning electron microscopy and energy dispersive X-rays to find the microstructure and composition. Upon deposition, In reacts with Ag to form In-AgIn2 composite. The intermetallic compound AgIn2 prevents the In layer from oxidation in atmosphere. Thus no flux is needed. Besides the fluxless feature. the low process temperature would significantly reduce the stresses developed due to thermal expansion mismatch comparing to the otherwise high temperature process with temperature exceeding the melting temperature. The multilayer bonding method also facilitates precise control of the alloy composition and the joint thickness. The new technique should find applications in the emergent high temperature electronic devices. (C) 2000 Elsevier Science S.A. All rights reserved.