Pressure-Less Sintering on Large Dies Using Infrared Radiation and Optimized Silver Sinter Paste

Abstract

Silver sinter material is highly considered as a promising lead free die attach material in recent years especially for high temperature power electronic packaging because of the high melting temperature of silver and its unique properties such as high thermal and electrical conductivity. Silver sintering process are generally classified as pressure and non-pressure sintering process based on the presence or absence of applied pressure during sintering process. Non-pressure sintering is the common process for power discrete application. However, conventional non-pressure sintering process carried out in a convection oven is not a favor sintering process mainly due to the long process time which requires up to several hours. In this paper, we demonstrated that sintering using infrared radiation is an alternative method for conventional non-pressure sintering process. This study revealed that sintering using infrared radiation is feasible and the total process time is only about 90 min. IR sintering with 90 min achieved the average die shear strength of about 30 MPa which is slightly higher than that obtained by 4 hours conventional non-pressure sintering. This observation indicates that the total process time of sintering can be reduced significantly using infrared radiation. The cross section images show that the sintered layer obtained by sintering with infrared radiation has a more uniform pores distribution compared to the sintered layer obtained by conventional non-pressure sintering. The average die shear strengths before and after 96 h pressure cooker test with condition of 100% RH at 110°C are relatively similar indicating that a high reliable sintered joint was obtained by sintering using infrared radiation. It is worth pointing out that no delamination in the sintered layer and void rate less than 1% were detected by scanning acoustic microscopy for the samples after 96 h pressure cooker test.