Lead Free Die Mount Adhesive Using Silver Nanoparticles Applied To Power Discrete Package

Abstract

Lead-free materials are required to replace conventional lead-containing solder for environmental protection. The Pb-rich solder die mount material in a high-power transistor package is required to be replaced by a silver adhesive paste. The silver paste has disadvantages such as low thermal conductivity and high electrical resistivity, since conduction paths are achieved only by mechanical contacts between silver particles. Recently, a new conductive paste containing silver particles and silver nanoparticles with a particle size of 3–7 nm in diameter was developed. The paste shows very low electrical resistivity of 6×10−6 ohm.cm, since the silver nanoparticles can be fused at temperatures below 200°C. We have been studying the possibility of the paste as a die mount material for high-power transistor packages. It was confirmed that the paste had a very high thermal conductivity of 51 W/mK. We fabricated a high-power transistor package using this paste. As a result, the package showed lower thermal resistance than that fabricated using silver paste or lead-containing solder. Moreover, the package is sufficiently reliable that it passed the thermal cycle and pressure cooker tests. This paste can be applied to a high-power transistor package in place of lead-containing solder.