Influence of Selected Design Variables on Thermo-Mechanical Stress Distributions in Plated-Through-Hole Structures

Abstract

Failure of plated-through-holes (PTHs) due to thermomechanical stresses is a well established cause of failure of multilayer printed wiring boards (MLBs). This paper uses the finite element method (FEM) to examine the nature of the stress distribution within the PTH structure when the MLB is subjected to thermal loads. Guidelines are laid out for realistic modelling of material properties and boundary conditions in the FEM model. Parametric studies are conducted to study the qualitative effect of several geometric parameters on the critical stresses in the PTH. Both traditional glass-epoxy (FR-4) MLBs and highly anisotropic Kevlar-polyimide MLBs are examined. Differences in behavior observed between the two materials underline the pitfalls in extending the standard design thumbrules for standard FR-4 MLBs to other MLB materials. The purpose here is to provide guidelines for the reliable design of PTHs. Actual fatigue life predictions are deferred to a later paper.