Thermal Stress Issues in Plated-Through-Hole Reliability

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 chapter uses the finite element method (FEM) to examine the nature of the stress distribution within the PTH structure when the MLB is subjected to uniform thermal loads as seen in operational environments as well as to examine the thermal transients seen in wave soldering. Guidelines are laid out for realistic modeling of material properties, boundary conditions, and stress averaging in the FEM model. Parametric studies are conducted on the critical stresses in the PTH to study the qualitative effect of several geometric parameters, including the effect of filling the PTH with solder. The purpose here is to provide an insight into the stresses that cause PTH failures and to establish guidelines for the reliable design of PTHs. Manufacturing-related problems such as defects and flaws in the plating material and actual life predictions are not addressed at this time.