Rapid equiaxed Cu3Sn formation and high-temperature reliability of transient liquid phase bonding with an Sn/2 μm Cu/Sn preform

Cu–Sn-based transient liquid phase (TLP) bonding has attracted significant attention for packaging inverter power modules, key components of electric vehicles. The Cu–Sn intermetallic compound (IMC) joints formed by TLP bonding offer excellent high-temperature stability but typically require long bonding times and high pressures. Moreover, the final Cu 3 Sn phase often develops columnar grains that degrade joint reliability. This study addresses these challenges by employing a Sn/2 μm Cu/Sn laminated solder preform, fabricated by inserting a 2 μm Cu foil between Sn foils, to bond a Cu chip to a direct bonded Cu substrate. The laminated preform enabled complete transformation of Sn into equiaxed Cu 3 Sn grains within 20 min, producing a stable, homogeneous TLP-bonded joint. After thermal aging at 150 °C for 1008 h, the joints retained shear strengths above 30 MPa. The suppression of columnar Cu 3 Sn growth was attributed to rapid consumption of the ultrathin Cu interlayer, which terminated Cu flux and promoted equiaxed nucleation at the joint center. These results demonstrate that the Sn/2 μm Cu/Sn laminated solder preform enabled rapid IMC formation while facilitating morphological control of Cu 3 Sn, ensuring improved long-term reliability. This approach offers a practical pathway for high-temperature, high-reliability interconnections in next-generation power electronic packaging.