Cu–Cu bonding using bimodal submicron–nano Cu paste and its application in die attachment for power device

The bimodal submicron–nano Cu paste was developed for the application in die attachment for power device, and robust Cu sinter joints could be realized at a low pressure of 0.4 MPa in N₂ atmosphere. The ratio of submicron-Cu and nano-Cu particles had a great influence on the bonding performance of Cu paste. The optimized content ratio of submicron-Cu and nano-Cu particles was 1:1, with which the high shear strength of 40 MPa could be achieved at 250 °C, and an ultra-high shear strength of 60.4 MPa could be reached at 300 °C. At the same time, the porosity of the sintered body could be reduced to 11.3%, while the resistivity could be reduced to 11.2 μΩ cm. Compared with the Cu sinter joint of pure nano-Cu paste at 300 °C, the shear strength of submicron:nano = 1:1 Cu paste was increased by 27.3 MPa, the porosity was reduced to 33.7%, and the resistivity was reduced to 16.7%. And the reasons for this phenomenon are explained from the packing density of the Cu particles, the size, and proportion of the Cu particles. The presented bimodal Cu paste possessed high bonding performance which had enormous potential in industrial production.