Effect of Oxygen Partial Pressure on Silver Migration of Low-Temperature Sintered Nanosilver Die-Attach Material

The low-temperature joining technique of silver sintering is being actively pursued in the power electronics industry as a lead-free die-attach solution for packaging power devices and modules. However, one of the concerns of this technique is the migration of silver at a high temperature. Recently, we have reported our findings of the migration of a low-temperature sintered nanosilver in dry air at a temperature over 250°1C. In this paper, we report our results of the effect of oxygen partial pressure on the migration kinetics of the sintered nanosilver at 400°C under an electrical field strength of 50 V/mm. The range of the oxygen partial pressure tested was between <; 0.01 and 0.40 atm. The silver migration kinetics were monitored by measuring the leakage current across a metal-finger pattern, which allowed the determination of the "lifetime," or the onset time for significant leakage current developed across the two electrodes. With decreasing oxygen partial pressure, the lifetime increases exponentially. Our results suggest that the concern for silver migration in a high-temperature application of sintered silver die attach can be effectively remedied through packaging to keep oxygen away from the silver joints.