WIREBOND DEFORMATION DURING MOLDING OF IC PACKAGES

During the transfer molding of IC packages, wirebonds are deformed by the action of flow-induced viscous forces acting along them. Excessive deformation of wirebonds could give rise to short circuits and bond p ull-outs. In this paper, the deformation of gold wirebonds during tran sfer molding of IC packages is studied using the finite element method . Hitherto, only elastic deformation of wirebonds has been considered In this paper, a more realistic elasto-plastic large-deflection model is employed The gold wire is assumed to be made of a bilinear strain h ardening material. It is shown that plastic deformation in the wirebon d can occur even if the melt flowrate is not very high. However, wireb ond deflection may still be within acceptable limits even though certa in portions of the wirebond have yielded plastically. The deformation of parabolic wirebonds under the action of melt flow both normal and p arallel to the plane of the wirebond, is also studied. The melt flow w ithin the cavity is simulated assuming creeping flow. Parametric studi es of the effects of wirebond dimensions, namely bond height, span and wire diameter, on wirebond deformation are also carried out.