Preparation and Application of Cu-Ag Composite Preforms for Power Electronic Packaging

Nano-silver and nano-copper can be effectively sintered at lower temperatures, to form the joints with high melting point meeting the needs of the interconnections of high temperature electronics. However, It has been concerned that the high cost and electromigration associated with the use of nano-silver, as well as the oxidation with nano-copper can somewhat hinder the further development and uses of these materials. In this work, we have developed micro-scale Cu-Ag core-shell composite particles by electroless plating, combining the excellent properties of copper and silver, which can potentially solve the identified problems. The mechanism of pretreatment and electroless plating in the process of preparation of these particles was explained. The composite preform was then prepared instantaneously using the particles by the electromagnetic pressing, which can significantly improve the quality of the joints formed in comparison with the direct powder sintering. Finally, the bonded structure using the preform was successfully prepared through low temperature sintering at 250 degrees C under a pressure of 3 MPa. Analyses of the sintered joints showed that the attachment layer had a uniform microstructure with the potential for high reliability under high temperature applications.