Pressureless sintering of nanosilver paste as die attachment on substrates with ENIG finish for semiconductor applications

Abstract

In order to overcome interfacial delamination of pressureless sintered nanosilver as die attachment on the ENIG finish, we tried to clarify the densification and interfacial diffusion behavior of sintering nanosilver paste on Au finish. Two different electroless nickel immersion gold (ENIG-1, ENIG-2) and one electroplated nickel gold (electrolytic Au) were compared in the aspects of mechanical, thermal performance, and microstructures. Delamination was found at the as-sintered Ag in the vicinity of Ag/Au interface in the ENIG-1. It was likely that too much Ag atoms was diffused into the ENIG-1, the left Ag atoms of the Ag-NPs in the vicinity of the interface are not sufficient to be densified as a robust sintered Ag joint at the higher temperatures. Electron backscattered diffraction (EBSD) results confirmed that the grain size, the high angle grain boundary, and the (111) texture lead to the rapid non-densifying diffusion of the Ag atoms with the ENIG. We proposed a modified sintering profile and the rougher ENIG-2 with thinner Au finish to reduce the non-densifying diffusion. The performance, and microstructures of the sintered Ag on the ENIG-2 confirmed that it is reasonable to enhance the sintered Ag on ENIG by reducing the rapid non-densifying diffusion at above 150 °C.