Comparison of the interfacial thermal resistivity of silver and solder die-attach using laser flash technique

Silver as a die-attach material is a promising alternative to solder as demonstrated by pressure-assisted sintering experiments on silver paste. Unlike solder, the higher operating temperature capability of silver makes it suitable for high-temperature power-device applications. The laser flash technique, which is widely used to determine thermal diffusivity of materials, was used to obtain the interfacial thermal resistances from the silver and solder-attached materials. The measurements were obtained from samples consisting of the die-attach material sandwiched between copper discs. By measuring the half-temperature rise-time of the sample's backside following the incidence of the laser-flash on the front, the thermal resistance contribution arising from the presence of the die-attach layer was obtained by analytical method. Finite element modeling (FEM) as a numerical method provided the identical results with the analytical method. It was found that using silver as the die-attach layer can almost eliminate the interfacial thermal resistance of the die-attach layer. Coating the copper substrate with gold also reduced the interfacial thermal resistance to about one-third when using reflowed solder as die-attach layer.