Kazuki Tateyama

Lead free die mount adhesive using silver nanoparticles applied to power discrete package

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 resist...

Evaluation of barrier metals of solder bumps for flip-chip interconnection

This paper describes the optimum thickness of barrier metals and the cause of the decrease in the shear strength of 37Pb/63Sn solder bumps for flip-chip interconnection. The authors evaluated the mutual diffusion and the shear strength of solder bumps on barrier metals. From aging test results with the Cu/Ti structure, when the thickness of the Cu film was greater than 10 /spl mu/m, the shear strength did not change from the initial value. In the Ni/Ti structure, where the Ni film had a thickness of 1.0 /spl mu/m, the shear strength also did not change from the initial value. In addition, it was confirmed that the decrease in the shear strength is caused by diffusion between Sn and Cu, or Sn and Ni, and oxidization of the barrier metals.