Wirebound deformation during molding of IC packages

Abstract

In this paper, the deformation of gold wirebonds during transfer molding of IC packages is analyzed using the finite element method. Hitherto, only elastic deformation of wirebonds has been considered. In this paper, a more realistic elasto-plastic model is used. The gold wire is assumed to be made of a bilinear strain hardening material. It is shown that plastic deformation in the wirebound can occur even if the melt flowrate is not very high. However, wirebound deflection may still be within acceptable limits even though certain portions of the wirebound have yielded plastically. The deformation of parabolic wirebonds under the action of melt flow, both normal and parallel to the plane of the wirebound, is also analyzed. An elasto-plastic and large deflection model is employed. The melt flow within the cavity is simulated using a creep flow model.