Effect of purity of Al interlayer on stress and thermal cycling durability of die-attach Ni-Sn joints

In this study, an effect of Al layer insertion to die-attach Ni-Sn joints with semiconductor chips by solid-liquid interdiffusion bonding on the stress and thermal cycling durability was investigated focusing on the purity of Al. The results showed that the Al interlayer significantly decreased the residual compressive stress in the semiconductor chips after bonding, and the use of 4N-Al (99.99 wt%) decreased the residual stress more significantly than the use of 2N-Al (99 wt%). Additionally, during thermal cycling up to 200 degrees C, a change from compressive to tensile stress occurred, which decreased with time; the decrease for 4N-Al was greater than that for 2N-Al. After 500 thermal cycles between - 40 and 200 degrees C, fewer voids were observed in the Ni-Sn SLID with Al interlayer joints than those in the Ni-Sn SLID joint, and the voids were fewer in the 2N-Al interlayer joint than in the 4N-Al interlayer joint; this suggests a balance in the relationship between stress reduction and thermal durability in the chip of die-attach joints. Therefore, it indicated that the use of Al interlayer and optimization of the composition are important to balance high stress reduction in the semiconductor chips and thermal durability of die-attach joints.