High Thermally Conductive and High Reliability Under-fill

摘要

The microelectronics packages are becoming smaller and thinner. Flip-chip technology is widely used in microelectronics package. Flip-chip package are progressing with multi functions in one chip. In this case, heat of the package becomes bigger. Flip-chip packages inside mobile phones and PDAs are in tight spaces and these devices are very thin. Therefore, it is difficult to make the heat sink. High thermally conductive under-fill material is effective to solve the heat dissipation issues removing heat to the substrate. Novel under-fill has to protect the package not only from the environment but also from heat. Until recently, silica filled under-fill was used for flip-chip applications, but it is not a good thermal conductor, since silica dose not have good thermal conductivity. Thermal conductivity of under-fill contains silica filler is around 0.4W/mK, so we chose an aluminum nitride as a filling material. But, conventional aluminum nitride particle could not be adapted for flip-chip packages since it's filler size was too large, therefore it is difficult to flow by capillary force. The various kinds of aluminum nitride were examined. High thermally conductive under-fill has been developed. It is filled with fine particle size aluminum nitride which will provide high thermal conductivity and good fluidity. And this under-fill realized over 2W/mK of thermal conductivity by control of loading level of the aluminum nitride filler. Also, this product satisfies the basic requirements for the under-fill, such as the JEDEC level 3 preconditioning test and temperature cycle test. The miniaturization of Flip-chip package is examined in many manufacturers. A thermal conductivity of underfill material has been regarded as important. Silica is contained in conventional under-fill as filler. Thermal conductivity of under-fill which contains silica filler is around 0.4W/mK. More than 1W/mK of thermal conductivity is required for high thermally conductive under-fill. However, it is difficult to confirm if thermal conductivities are more than 1W/mK when silica is chosen as filler, since thermal conductivity of silica is about 1.3W/mK. We chose an aluminum nitride as a filling material. When we chose aluminum nitride as filler, various evils happen. We overcame the evil this time and developed high thermally conductive and high reliability under-fill material. We report it about process of development.