Bonding 1200 V, 150 A IGBT chips (13.5 mm × 13.5 mm) with DBC substrate by pressureless sintering nanosilver paste for power electronic packaging

The insulated gate bipolar transistor (IGBT) is a minority-carrier device with large bipolar current-carrying capability and high input impedance. The IGBT has been used in many applications in power electronics. In this study, pressureless sintering of nanosilver paste has been studied for bonding large area power chips, e.g., 12 kV 100 A IGBT applications. The sintering temperature was reduced to 250 °C for only 10 min. The heating rate was adjusted to 5 °C/min. Void ratio in the bond-line before and after sintering was analyzed by X-ray transmission. It was found that the void ratio before sintering was successfully controlled below 1% of the joint area. X-ray images also showed that the void ratio was lower than 2% after sintering. Such low void ratio should have almost no impact on the thermal and electric properties of the pressureless sintered nanosilver joint. The more the voids before sintering, the more the formation of voids after sintering. Die-shear tests were also performed for the 10 mm × 10 mm sintered joints of bonding dummy dies and substrates at a shear speed of 4 × 10^-4 ms^-1 at room temperature. Results showed that average shear strength of higher than 40 MPa could be obtained for the pressureless sintered joints. Fracture surfaces of the sintered nanosilver joints were observed by scanning electron microscopy (SEM). SEM images showed that significant plastic flow occurred in the sheared joint because of the presence of dimples and the fracture of the sheared silver joint was a cohesive failure.