Thin-film metallization and micro-assembly driven comparative failure modes in advanced ceramic packaging under thermal cycling

AlN and Al₂O₃ ceramic substrates are increasingly adopted in high-performance electronic packaging owing to their excellent thermal conductivity, electrical insulation, and mechanical strength—features that are crucial for heterogeneous integration systems. However, compare with the extensively studied FR4-based structures, the reliability degradation of ceramic-based solder joints under thermal cycling, particularly the processing–structure–failure relationship, remains insufficiently understood. In this work, AlN- and Al₂O₃-based flip-chip assemblies were fabricated through thin-film metallization, micro-ball bumping, thermocompression bonding, and underfill dispensing. The thermal fatigue behavior of SAC305 solder joints was systematically investigated through combined experimental characterization and finite element simulation. After 1000 thermal cycles, distinct cracking patterns emerged: AlN-based joints exhibited cracks at both upper ((Pt, Au)-Sn IMC/solder) and lower ((Cu, Ni, Au)₆Sn₅ IMC/solder) interfaces, whereas Al₂O₃-based joints fractured only at the upper interface. Finite element analysis revealed that underfill effectively mitigated in-plane (xy) shear stresses but failed to suppress out-of-plane (z-axis) tensile stresses, which dominated crack initiation and propagation. Crack formation was more severe in the AlN system due to higher mismatch-induced stress and greater strain energy accumulation, leading to earlier crack onset and faster propagation. All cracks developed via microvoid nucleation and coalescence. Cs-corrected STEM further clarified the interfacial IMC structures and elemental site occupancies, showing that Ni preferentially occupied Cu2 lattice sites, whereas Au substituted Cu1 sites in (Cu, Ni, Au)₆Sn₅. These findings elucidate how processing-induced interfacial architecture and substrate-dependent stress evolution jointly govern the reliability of ceramic-based solder joints, providing guidance for designing next-generation high-power electronic packaging.