Low-Temperature Cu-Cu Bonding Using Spark Plasma Sintering System

Diffusion bonding of Cu bars without high vacuum and super-flatening bonding surface was investigated using spark plasma sintering (SPS) system for low-cost Cu-bulk-joint products. Oxygen-free Cu bars were set in graphite jigs, and were moderately compressed due to thermal expansion difference between graphite and Cu. The bonding temperature was measured directly on the Cu bars using a thermocouple. Tensile strength of the Cu-Cu joints increased gradually with increasing bonding time up to 30 min at 350°C and 400°C (respectively, 0.46 and 0.5 Tm, where Tm is Cu melting temperature), and achieved to 25 and 33 MPa, respectively, which were about one order of magnitude lower than the tensile strength of base metals. While, the tensile strength for those bonded at 300°C for 60 min exhibited about 7 MPa. This suggests that the temperature is not enough for removing oxide scale at the Cu-bar surface and/or for enhancing Cu-atom diffusion.