Effect of bonding interfacial microstructures on the properties and reliabilities of Cu–Cu joints

Cu–Cu joints with various interfacial microstructures were fabricated, by applying different annealing conditions to the joints to trigger different amounts of recrystallization and grain growth at the bonding interfaces. Three distinct interfaces were obtained, including planar, zig-zag, and recrystallized. The joints with the recrystallized interfaces possessed superior pull strength exceeding 50 MPa, whereas for the planar-interface joints it was only 15 MPa. Moreover, after 1000 cycles of thermal cycling tests (TCTs), the resistance increase for the recrystallized joints was as low as 3.95%, which outperformed the planar-interface joints (16.67%) and zig-zag-interface joints (9.69%). Thermal stress induced fractures were prone to happening at the planar-type interfaces, while the recrystallized interfaces exhibited excellent resistance to thermal fatigue. This study offers understandings on the thermal and mechanical reliabilities for the Cu–Cu joints with various types of the bonding interfaces, fabricated intentionally by tailoring the bonding parameters. We highlight the influence of the bonding interfacial microstructures on the bonding strengths and TCT reliabilities.