Evaluation of Microscopic Strain Distribution of Low-Temperature Sintering Die Attach in Thermal Cycling Test

The microscopic strain distribution of the low-temperature sintering die attach in a power module during the thermal cycling test was evaluated through finite element analysis (FEA). We targeted a power module that joined a silicon chip to the direct bonding copper substrate with a low-temperature sintering joining technique. We targeted sintered copper made with copper oxide particles (200 nm) and sintered silver made with micro silver particles (3 um) as the die attach materials. We estimated the mechanical properties of these materials with tensile and three-point bending tests results. Sintering conditions were set to 623 K for 15 minutes at 4 MPa in a hydrogen atmosphere for sintered copper and set to 573 K for 10 minutes at 10 MPa in the air atmosphere for sintered silver. The macroscopic strain of the sintered layer in the evaluation module was calculated through FEA with the estimated material properties. The thermal cycling condition was set from 233 to 473 K. The calculated macroscopic stain was used as the boundary condition of a microscopic FEA model that reproduces the microporous structure of the sintered layer. We calculated the microscopic strain distribution at the necks and around the voids using this model. We investigated the difference in strain distribution between the sintered copper and sintered silver and compared FEA results with experimental results.