Application and reliability analysis of sintered silver preforms for die attachment of wide bandgap devices

Abstract

Sintered nanosilver paste has been demonstrated to have superior electrical, mechanical, and thermal properties as compared to other state-of-the-art die attach materials available today. However, prior to sintering, the material has to be applied on the substrate surface in the form of a wet paste. In order to ensure adequate wetting of the die bonding surface, a manual "scrub-in" step is typically performed using mild pressure. The consistency of the paste and the scrub-in procedure poses a challenge in obtaining a bond line with uniform thickness. A sloping bond line makes it susceptible to fracture at the narrow end as a result of temperature cycling. Moreover, for any applications involving a stacked or 3D architecture, near flat die surfaces are a necessary requirement. Nanosilver preforms are proposed as a solution to address this issue. Die shear test results and cross section observations collected before and after thermal shock testing of die attached using nanosilver preforms is presented.