Pressure-adaptive core–shell liquid metal microspheres for reliable flip-chip interconnects

Conventional anisotropic conductive adhesive (ACA) face challenges in achieving reliable vertical electrical interconnections under low bonding pressure, particularly for small-sized dies and flexible substrates, due to their reliance on rigid conductive particles requiring high-pressure bonding. Liquid metal (LM), with high conductivity and intrinsic flexibility, offer promise for next-generation flexible electronics but suffer from leakage and corrosion risks. Here, a core-shell structured LM@Ag microsphere is synthesized via in-situ chemical reduction, featuring a deformable LM core encapsulated by a robust Ag shell. This design effectively mitigates LM leakage while combining high electrical conductivity of 2.94 × 10 5  S m −1 and pressure-adaptive deformability. When incorporated into epoxy resin (Ep) mixture, the LM@Ag/Ep-ACA enables stable electrical interconnections under a low bonding pressure of 1 N for radio-frequency identification (RFID) tag packaging with small-sized chip of 0.186 mm 2 . The LM@Ag-based ACA also achieve robust chip shear strength of 53.98 ± 3.06 MPa, and maintain functionality after 85 °C/85 % RH test for 168 h and 100 thermal shock cycles ranging from −40 °C to 85 °C. The synergistic integration of metallic conductivity and mechanical compliance in LM@Ag microspheres opens avenues for advanced flexible electronics, particularly in applications demanding pressure-sensitive reliability and dynamic durability.