Nine Point Bending Test Technique for Understanding of Sintered Silver Die Bonding Failure Mechanism

The Sintered silver (s–Ag) die degradation is commonly evaluated by thermal shocked test (TST), which evaluates the material’s durability against a heating/cooling cycle. Materials with different coefficient of thermal expansion (CTE) give rise to thermal out-of-plane deformation surrounding the bonding part, which deteriorates s–Ag die part by repeated thermal and mechanical stress during TST. For the safe and reliable design of s–Ag die toward long-term durability, the contribution of thermal and mechanical stresses to degradation should be understood separately. Clarify the overall s–Ag die degradation mechanism during TST compared to the new mechanical bending test that can apply out-of-plane deformation. The authors propose a new mechanical bending test technique, called the nine-point bending (NBT) test, which can provide out-of-plane deformation with a s–Ag die-attached specimen as TST like. By comparing NBT and TST, the degradation mechanism of the s–Ag die-attach element can be understood from both thermal and mechanical aspects. In scanning acoustic tomography (SAT) analysis, a similar degradation ratio between NBT and TST is obtained, which indicates that mechanical stress plays a significant role in deteriorating s–Ag die layer in TST. After 1000 cycles, however, cracking and s–Ag material aging coexist in TST only, destabilizing s–Ag die fracture. s–Ag main degradation cause in TST is clarified with mechanical stress by comparing NBT. In addition, thermally material aging destabilized the s–Ag degradation during TST.