Evaluation of Out-of-Plane Thermal Conductivity and Shear Strength of Copper Mesh/Epoxy Adhesive Film

Abstract

Thermally conductive adhesives are essential thermal interface materials for high-power electronics, but achieving low out-of-plane thermal resistance while maintaining adhesive strength remains challenging. Herein, we propose a copper mesh/epoxy adhesive in which a preconstructed continuous metallic framework is embedded in a thin epoxy adhesive layer to form out-of-plane heat conduction pathways without relying on conventional highly filled filler-dispersed systems. The effects of pressure during curing on the residual epoxy layer, out-of-plane thermal conductivity, and single-lap shear strength were systematically investigated. Cross-sectional SEM observations showed that applying pressure during cure reduced the residual epoxy layer between the aluminum adherend and copper mesh; the epoxy layer thickness was less than 0.1 μm over approximately 15% of the copper mesh region. From the epoxy thickness distribution, the thermal conductivity of the press-cured adhesive was estimated to be 13.0 W/(m·K), approximately 30 times higher than that of the adhesive cured at atmospheric pressure. Transient measurements also showed a high effective thermal conductivity of 26.7 W/(m·K), supporting the formation of localized heat conduction pathways. Steady-state measurements demonstrated that promoting contact between the copper mesh and adherend reduced the area thermal resistance from 2.18 to 0.150 K·cm2/W, corresponding to a 93.1% reduction, and yielded an apparent thermal conductivity of 5.06 W/(m·K) even including interfacial thermal resistance. However, epoxy-layer thinning decreased the single-lap shear strength to 4.4 MPa, indicating the need to improve interfacial adhesion. These results demonstrate that press-assisted contact between a preconstructed copper mesh framework and adherends is a promising strategy for reducing out-of-plane thermal resistance in thin epoxy adhesive layers.