Failure mechanisms of sintered silver interconnections for power electronic applications

To secure power devices to a substrate, solder materials are typically used. An alternative technique to produce silver interconnections by pressure-assisted sintering of micron-sized silver flakes is known as Low Temperature Joining Technology (LTJT). In principle, the LTJT shows a superior electrical and thermal performance compared to solders. In addition LTJT interconnections can be employed at temperatures exceeding 200°C (390°F). However, one important aspect of power electronics is their design for reliability. It is important to know failure mechanisms in sintered silver interconnections to assess and improve reliability based on finite element simulation. The goal of this work was to examine failure mechanisms in sintered silver interconnections due to thermo-mechanical cycling. Investigations were carried out on tensile specimens and in thermo-mechanical shock tests on Si-MOSFETs joined to a copper substrate. It is concluded that a dominant mechanism of deformation in sintered specimens is plasticity. Nevertheless, a significant fracture mechanism in the examined sintered interconnections is intergranular fracture, presumably due to grain boundary porosity in the sintered specimens. The study is concluded with a brief examination of the lifetime of sintered joints in thermal shock cycling.