Indium-based self-confining metal foam thermal interface materials for thermo-mechanical-interface coupling in next-generation large die FCBGA packages

High-power density and large die flip-chip ball grid array (FCBGA) packages posed significant challenges for heat dissipation and stress relief between the die and lid. Traditional thermal interface materials (TIMs), such as polymer-based gels and metallic solders, were limited by either low thermal conductivity, weak interfacial bonding or high elastic modulus, resulting in insufficient thermal management and elevated interfacial stress. In this work, a flexible interlayer strategy was proposed to decouple thermomechanical stress in TIMs. Implementing this approach, a novel In/self-confining foam Cu/In structure was developed. By precisely tailoring the porosity of the copper foam and applying surface metallization, the resulting material achieved a remarkable combination of high thermal conductivity (23.3–76.0 W/m·K), low Young's modulus (2.7–10.2 GPa), and robust interfacial shear strength (2.23–3.65 MPa), presenting a promising TIM1 solution. Flexible foam Cu interlayer with varying porosity was modified using electroless Ni-P and electroplated Ag coatings, which enabled strong metallurgical bonding while self-confine excessive In infiltration into the foam Cu during fabrication process. Finite element simulations demonstrated that increasing porosity significantly reduced interfacial stress. Shear strength tests and failure analyses revealed that optimized foam Cu TIMs outperformed traditional TIMs in mechanical performance. These findings offered a promising flexible foam interlayer and self-confining design strategy for next-generation TIMs in large die FCBGA packages, where effective heat dissipation, stress accommodation and robust interfacial bonding were critical. • Ni–P/selected distributed Ag coating enables strong bonding while blocking In infiltration into foam Cu. • Reveals curvature-driven Gibbs–Thomson IMC growth. • In/Foam Cu/In TIM1 achieves high thermal conductivity and stress relief.