Microwave hybrid heating assisted solid-liquid interdiffusion bonding of Cu/In-Ag/Cu joints: intermetallic growth, mechanical properties, and reliability

Solid-liquid interdiffusion (SLID) bonding offers high-temperature-stable die-attach interconnects for third-generation semiconductor power devices, but conventional SLID processes require prolonged isothermal holding to achieve complete conversion of the solder into intermetallic compounds (IMCs). Here, microwave hybrid heating (MHH) combined with nano-Ag reinforcement was employed to accelerate full IMC formation in Cu/In-Ag/Cu joints. Using a bulk SiC susceptor, molten In is proposed to absorb microwave energy directly, providing additional volumetric heating that promotes IMC growth. Kinetic analysis revealed that Cu 11 In 9 growth progressively shifted from bulk-diffusion to grain-boundary-diffusion control with increasing bonding temperature (170–250 °C). Among Ag contents of 10–40 wt.%, 30 wt.% nano-Ag was optimal. Compared with micro-sized Ag, nano-Ag dissolved more uniformly, producing dense full IMC Cu/In-30Ag/Cu joints free of residual In and large voids after 120 min at 250 °C. The optimized joints achieved a shear strength of 28.05 MPa, more than four times that of the Ag-free joint (6.02 MPa). Lower Ag contents resulted in incomplete conversion, whereas 40 wt.% Ag caused coalescing porosity that limited the shear strength to approximately 11.3 MPa. Electromigration testing showed that the (Ag, Cu)In 2 phase suppressed Cu transport, resulting in greater microstructural stability than that of the Ag-free joint. During aging at 280 °C, the shear strength of the optimized joint decreased gradually to 4.17 MPa after 675 h, as Ag-containing IMCs delayed void growth and microstructural degradation. Overall, the combined MHH and nano-Ag strategy promotes full IMC formation while improving joint uniformity, mechanical performance, and long-term reliability, providing an effective bonding approach for high-temperature packaging of third-generation semiconductor power devices.