Influence of temperature and microstructure on the mechanical properties of sintered nanosilver joints

In order to study the effect of temperature on the mechanical behavior of sintered nanosilver joint for die attachment in power electronics, we developed a non-contact displacement detecting system (NDDS) for measuring the evolution of displacement of joints. Based on a digital image correlation method, the NDDS is capable of detecting a minimum displacement of 3 μm. With the aid of this NDDS, stress-controlled monotonic and cyclic shear tests were conducted on sintered nanosilver joints at various temperatures using an electronic fatigue testing machine. Scanning electron microscopy (SEM) was used to investigate the correlation between loading conditions of the joints and particle size of the sintered nanosilver. The particle size was found susceptible to deformation mode, temperature and holding time. While the particle size is always larger in the cyclic tests than in the shear tests, temperature and holding time play a more important role in the process of particle growth. The shear strength and fatigue life of the sintered nanosilver joints were found to decrease with increasing particle size. This is attributed to the dissolving of the grain boundaries along with the particle growth, which impairs the ability of the sintered nanosilver in inhibiting deformation and retarding crack propagation.