Characterizations of Nanosilver Joints by Rapid Sintering at Low Temperature for Power Electronic Packaging

Nanosilver paste is a promising lead-free die-attach material suitable for power electronic packaging, particularly for high-temperature applications. Compared with traditional hot pressing to sinter nanosilver, rapid sintering by a pulse current is able to sinter nanosilver in less than a second. To investigate the nanosilver sintering process during rapid sintering, we characterize the temperature field of a nanosilver joint by using an infrared camera. The temperature field is analyzed as a function of current magnitude and current-on time. The relationship between the temperature field and the shear strength of joint is discussed to optimize the rapid sintering parameters. Results show that the joint's temperature-time curve varies with the current-on time. The shear strength can be up to 40 MPa, which is comparable to the robust hot-press sintered joint, when the peak temperature reaches above 400 degrees C. The microstructure of these joints is porous with a particle diameter of similar to 400 nm, and this aids in releasing the internal stresses resulting in higher shear strength.