Design of latent-curing system to decouple sintering and curing reactions for dense Ag necking formation in Ag/epoxy composite die attach

초록

Ag sintering is recognized as a next-generation die-attach technology for wide-bandgap power semiconductor due to its high melting point and excellent thermal/electrical conductivities. The process temperature is restricted to below 300 degrees C to avoid thermal stress from coefficient of thermal expansion (CTE) mismatch or direct thermal damage on packaging materials or semiconductor, which often results in residual porosity and limited densification within the sintered layer. While epoxy is added for mechanical reinforcement, conventional systems suffer from premature curing, where a rapid increase in viscosity hinders Ag particle rearrangement and neck formation. To address this, we developed a latent-curing epoxy system that maintains low viscosity during the initial Ag sintering stage, allowing for sufficient particle contact and densification before gelation. The correlation between latent curing and thermal conduction pathway development was quantitatively analyzed using scanning electron microscopy (SEM) image-based 2D finite element method (FEM) for heat transfer simulations. The proposed Ag/epoxy composite die attach material exhibited a thermal conductivity exceeding 170 W/m & sdot;K and a shear strength of 56.1 MPa, significantly outperforming conventional premature-gelation systems. This finding demonstrates that the synergistically designing hybrid Ag powders and latent curing kinetics is a critical factor for optimizing the microstructure-property relationship in sintered joints.

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