The effects of in-plane orthotropic properties in a multi-chip ball grid array assembly

Abstract

It has long been recognized that the properties of printed circuit boards and BGA laminates in the out-of-substrate direction differ greatly from the properties in the plane of the substrate. In this paper the variation of in-substrate-plane properties is examined, both in mechanical testing and in finite element analysis. It is shown that the in-substrate-plane coefficient of thermal expansion and modulus of elasticity are influenced significantly by the direction of the traces in the copper layers of the substrate. The impact of these on warpage is explored for a BGA assembly. It is concluded that for multichip products it is necessary to consider the effects that differences in in-substrate-plane mechanical properties may have on the finished product.