Effect of Chip Size and Shape on the Thermal Stress and Strain of Sintered Ag Joints During Thermal Cycling

With the rapid development of wide bandgap (WBG) semiconductors, the service temperatures of high-power modules frequently reach or even exceed 250 °C, which poses a challenge to traditional die-attach materials. Sintering Ag paste has been considered a reliable die-attach material for power module packaging due to the high melting point, high electrical conductivity, and high thermal conductivity of Ag. The reliability of sintered Ag has been the focus of research as reliability experiments are complex. In this study, we used finite element analysis (FEA) to investigate the size and the shape effect of chip on the thermal stress and strain of sintered Ag layer during different thermal cycling conditions. The chip size can have a significant impact on the stress and strain at the corners of sintered Ag layer (the most concentrated region of thermal stress). This makes sintered Ag layers behave differently during thermal cycling: sintered Ag with smaller chips may show no accumulation of equivalent plastic strain during long-time thermal cycling, which makes them more reliable. The chip shape can have a substantial impact on the stress and strain distribution although stress and strain concentrations are still found at the corners of the sintered Ag layer. The stress concentration at the corner will decrease as the length of the longer edge increases. We think that this work can improve the understanding of the influences of chip size and shape on the thermal stress derived from the coefficient of thermal expansion (CTE) mismatch and provide a new perspective for both researchers and engineers to consider the reliability of sintered Ag joints.