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Large-area Die Attachment and the Surface Finish Effect on Bonding Strength of Joints in High-power Electronics Using a Low-temperature Sinterable Cu Nanoparticle Paste

Packaging of power electronics and third-generation semiconductor devices poses a challenge for the die attachment materials to be used in high-power electronics to ensure the joints capable of withstanding temperature up to 300 ºC. To this end, low-cost Cu paste is a promising candidate and has drawn increasing interest recently. In the present study, sinterability of Cu nanoparticle paste under different sintering process conditions and its applicability in large-area die-attachment with different die surface finishes have been studied systematically. The shear strength of 3×3 mm2 Cu/Cu-paste/Cu joints sintered in nitrogen without pressure can reach 25.4 MPa, and the joints sintered in air with only 0.5 MPa pressure show the shear strength higher than 30 MPa, indicating the excellent anti-oxidation performance and sinterability of the Cu paste. In addition, the influence of die size and surface finish on mechanical performance of sintered joints has also been studied. For relatively large size (with area of 5×5 mm2) die attachment joints, sintered Cu/Cu-paste/Cu joints have shear strength up to 20.6 MPa, followed by Ag/Cu-paste/Cu joints with 19.5 MPa. Even for Ni/Cu-paste/Cu joints, in which there is weak diffusion, their shear strength can also reach 12.7 MPa. Overall, the Cu paste exhibits excellent surface finish suitability and high potential for a broad application in the packaging field of power electronics.