Degradation Mechanism of Silver Sintering Die Attach Based on Thermal and Mechanical Reliability Testing

This article investigates the degradation mechanism of sintered silver (s-Ag) layer in silicon carbide (SiC) die attach by means of thermal shocked test (TST) and nine-point bending test (NBT). TST can thermally provide out-of-plane deformation with s-Ag die layer, whereas NBT developed by the authors can mechanically provide the out-of-plane deformation. Two types of Ag paste (NP: nanopaste and NMP: nano- and micropaste) are employed, which are sintered with 300 °C for 10 min under 60-MPa pressure for SiC die attach. TSTs are conducted under thermal cyclic loading between −40 °C and 150 °C with trapezoidal waveform for 60 min per a cycle. NBTs are conducted under cyclic mechanical loading between 0 and 300 N with triangle waveform for 3 min per a cycle at 150 °C. Scanning acoustic tomography (SAT) evaluates the die-attach delamination during TST and NBT, which starts from the edge of the die. Cross-sectional scanning electron microscopy (SEM) observation demonstrates that mechanical cracking and material aging in s-Ag layer coexist after TST under the −40 °C to 150 °C conditions only. A damage parameter (DP) proposed in this study works well to fit the delamination area ratio in the cracking and cracking-aging specimens separately after 1000 cycles. Molecular dynamics (MD) simulation and classical pore growth discussion suggest that pores can grow under only tensile stress state at high temperature, which would have given rise to the difference between the two degradation mechanisms.