High reliable silver sintered joint on copper lead frame by pressure sintering process

Abstract

Lead-free technique for die attach application has attracted raising attention in recent years. Low temperature silver sinter has demonstrated significant develop over the past years to be considered one of frontrunner lead-free die attach solution. Pressure silver sintering offers superior thermal and electrical conductivity as well as mechanical properties compared to non-pressure silver sintering. The total process time of pressure sintering is almost 8 times shorter than that of non-pressure sintering. In this study, we compared silver sintered joint created on Ag plated and bare Cu TO 220 lead frame obtained by non-pressure sintering. Additionally, a comparison of non-pressure sintering and pressure sintering on bare Cu TO 220 lead frame was also carried out. For non-pressure sintering, the average die shear strength for Ag plated lead frame is almost three times higher than for bare Cu lead frame. This observation can be ascribed to the self-diffusion of Ag is higher than for interdiffusion between Ag and Cu. By applying pressure during sintering process, the bonding strength of sintered joint on bare Cu lead frame can be increased significantly. We further observed that the die shear strength tested at 260 °C is higher than those tested at RT. Furthermore, the die shear strength increased after temperature cycling test with a condition of −55 °C/+150 °C. It is very likely that the sintering process continue to occur at high temperature resulting in higher bonding strength. The present study clearly demonstrated that high reliable silver sintered joint can be created on bare Cu lead frame by pressure sintering.