Reliability and Characterization of Nanosilver Joints Prepared by a Time-Reduced Sintering Process

This study investigates the power cycling reliability of nanosilver sintered joints formed by a time-reduced sintering process, designed for use on a die bonder. A range of sintering parameters, reflecting different levels of manufacturability, were used to produce sintered joints in respect of shear strength and porosity, within a process cycle time of a few seconds. The reliability of the sintered attachments were evaluated against Pb5Sn solder joints under constant temperature swing power cycling conditions over the range 50 to 200 °C. The thermal performance and microstructural changes of the sintered joints were monitored and evaluated non-destructively at regular intervals using transient thermal impedance and X-ray computed tomography. The results show that sintered joints with higher shear strengths (>50 MPa) and lower porosities (<25 %) tend to maintain their thermal performance up to ~100k power cycles before gradual degradation occurs. Sintered joints with intermediate shear strengths (20 to 40 MPa) and with corresponding analogous porosities (35 to 51 %) also demonstrated comparable power cycling behavior; exhibiting a progressive decrease in effective thermal conductivity with increasing cycles. The evaluated lifetime of sintered joints with the highest shear strengths were found to be at least double those for the lower shear strength joints, and up to fourteen times those of a Pb5Sn solder die attachment. Even the most porous sintered joints exhibited lifetimes appreciably longer than a Pb5Sn die attachment. Degradation in thermal resistance was seen to correlate with observed microstructural changes, with a dependence on initial sintering parameters.