Effect of surface finish metallization layer on shearing fracture toughness of sintered silver bonded joints

In this paper, the effect of different surface finish metallization layers (Cu, Ni, Au and Ag) on the shearing fracture toughness of sintered Ag bonded joints under various sintering temperatures is investigated based on end-notch flexure (ENF) test. The results show that the shearing fracture toughness for different kinds of specimens all increase with the sintering temperature augment. The sintered Ag/Ag joint shows the highest shearing fracture toughness while the sintered Ag/Ni joint shows the lowest. The average shearing fracture toughness of the Ag/Cu joint is very close to the Ag/Au joint when sintered from 240 °C to 280 °C, whereas the former became much higher when sintered under 300 °C. By statistically analysis of crack propagation paths, interface microstructure characteristics, and interface reaction, it is found that the main factors affecting the discrepancy of the shearing fracture toughness for different metallized layers are the interface connection ratio and contact angle. A higher interface connection ratio and lower contact angle can increase the actual crack resistance and lower down stress concentration at the bonding interface, which leads to the discrepancy of shearing fracture toughness correspondingly. The different inter-diffusion rates for Ag and various metallization layers are also clarified. This study could deepen the understanding of the metallization layer effect on the shearing fracture behaviors of sintered silver bonded joints.