Low thermal expansion and high thermal conductivity in epoxy molding compounds achieved via a dual-strategy of negative thermal expansion Cu2V2O7 and conductive fillers

Thermomechanical reliability in highly integrated 3D packaging is critically challenged by the coefficient of thermal expansion (CTE) mismatch among constituent materials. Employing negative thermal expansion (NTE) materials enables precise CTE tailoring of epoxy molding compounds (EMCs). This study reports a synergistic approach by incorporating NTE Cu 2 V 2 O 7 (CVO) with highly thermally conductive fillers (Al 2 O 3 and diamond) into a Bisphenol F epoxy to form a low thermal expansion EMC with high thermal conductivity. For the composite containing 70 wt % CVO, the CTE 1 (below the glass transition temperature, T g ) is 20.9 × 10 −6  °C −1 , while the CTE 2 above T g is 73.2 × 10 −6  °C −1 . Remarkably, the composite with 40 wt % CVO and 40 wt % diamond achieves a significantly lower CTE 1 of 16.5 × 10 −6  °C −1 and CTE 2 of 25.3 × 10 −6  °C −1 . Compared to epoxy with the CTE 1 and CTE 2 of 76.1 × 10 −6  °C −1 and 174 × 10 −6  °C −1 , it achieves a substantial reduction up to 78 % in CTE 1 and 86 % in CTE 2 . Moreover, these CTE 1 and CTE 2 closely match those of Cu bump (17 × 10 −6  °C −1 ) and RDL in IC, thereby mitigating thermal stress induced by CTE mismatch. Notably, this composite achieves a remarkably high thermal conductivity of 2.00 W m −1  °C −1 at room temperature, surpassing the ideal value of 1 W m −1  °C −1 and showing a 733 % enhancement over epoxy. This work presents an unconventional method to design advanced EMC by incorporating both NTE and highly conductive fillers. This strategy helps to achieve the low thermal expansion and high thermal conductivity simultaneously, potentially offering insights for high-end electronic packaging materials.