Development of transient liquid phase soldering process for LSI die-bonding

For high-power semiconductor devices with Cu lead-frames in plastic packages, die-bonding process that can obtain a heat-resistant bond (with high melting point) without large residual stress has been developed by applying transient liquid-phase bonding to the soldering process. A three-layered solder sheet the inner layer of which is 95Pb-5Sn solder and the surface layers of which are Pb-Sn eutectic solder is used as the bonding material. The bonding temperature is about 460 K so as to melt only eutectic layers. The eutectic layers are isothermally solidified and the melting point of the bond rises to over 520 K by a two-hour heat treatment at the bonding temperature. As a result, a heat-resistant bond can be obtained whose residual stress can be reduced by more than 1/2 by a low-temperature process