Constrained Sintering of Silver Circuit Paste

Abstract

Densification kinetics and stress development during constrained sintering of a silver film on a rigid silicon substrate have been studied. Compared with free sintering, the sintering of constrained silver film exhibits a much lower densification and slower densification kinetics. The densification‐controlled mechanism changes from fast grain‐boundary diffusion kinetics for free sintering to slow lattice diffusion kinetics for constrained sintering. The in‐plane tensile stress developed during constrained sintering of silver film, measured using a noncontact laser‐scanning optical system, increases rapidly to a maximum level of 1.0–1.5 MPa initially, gradually decreases, and then becomes constant at 0.8–1.0 MPa. The maximum stress observed increases with increasing sintering temperature as a result of the faster densification rate. It is believed that the retardation of densification kinetics of constrained silver film is caused by a change in densification mechanism and the existence of in‐plane tensile stress.