Heat-resistant die-attach with cold-rolled Ag sheet

This work introduces a bonding technology that employs a cold-rolled Ag sheet, which provides a unique reaction in air, to achieve low-pressure and low-temperature die-attachment for wide-bandgap semiconductors. The cold rolling of the Ag sheet induces grain refinement down to a sub-micron level with high residual stress, which is the driving force for hillock growth on the Ag sheet, resulting in intimate bonding. The detailed mechanism underlying the hillock joining was investigated via transmission electron microscopy (TEM). TEM images and electron-diffraction patterns showed that a large quantity of self-generated Ag nanoparticles formed in the contact area between two Ag substances.