Simplification of Low-Temperature Sintering Nanosilver for Power Electronics Packaging

Conventional solders cannot meet the requirements for high-temperature applications. Recently, a low-temperature sintering technique involving a nanosilver paste has been developed for attaching semiconductor chips to substrates. Sintered nanosilver joints showed high reliability in high-temperature applications. We used the nanosilver paste to attach 10 mm x 10 mm chips by introducing a pressure as low as only 1 MPa during drying at 185A degrees C. Die-shear tests showed that shear strengths of higher than 50 MPa could be generated by applying 5 MPa at 225A degrees C for only 10 s or 1 MPa at 150A degrees C for 600 s, followed by sintering for only 60 s at 275A degrees C. The sintering temperature could be reduced to 250A degrees C in most applications with a slight reduction in shear strength. As a result of good bonding, significant plastic flow and ductile fracture of the sheared silver joint could be observed by scanning electron microscopy (SEM). SEM also showed that the fracture of the sheared silver joint was a cohesive failure.