Thermomechanical analysis and fatigue life prediction of plated-through-holes in multilayered printed wiring boards.

摘要

Plated-Through-Holes (PTHs) are holes in Multilayered Printed Wiring Boards (MLBs) which are plated with conductive material to provide electrical interconnections between the conductive patterns in the MLBs. In this dissertation thermomechanical analyses are performed to investigate fatigue failures of PTHs in rigid organic MLBs subjected to temperature cycling. Parametric linear analyses are performed to investigate the qualitative/quantitative effects and relative severities of several geometric and material parameters on critical stresses in the PTH. This is followed by nonlinear analyses of stress and strain through finite element methods (FEM) to compute the plastic strain history in the PTH during thermal cycling. The strain history is then used in phenomenological fatigue damage models to predict the fatigue life for crack initiation in the plating. The numerical results are compared with experimental data from an extensive industrial test program on PTH reliability in Kevlar-epoxy MLBs.;In order to provide material property data inputs for the PTH analysis this dissertation also includes thermomechanical constitutive characterization of fabric-reinforced composite MLBs. The fabric is woven from yarn bundles, each of which is a unidirectional fiber-reinforced composite. Transversely-isotropic effective thermomechanical properties are obtained for these yarn bundles from a generalized, self-consistent Mori-Tanaka scheme. The technique can address imperfect and damaged interfaces, radial variations in interphase properties and multiple coatings. The yarn properties form inputs to a numerical model which simulates the fabric weave micro-architecture to obtain effective MLB properties. Orthotropic effective thermomechanical properties are obtained for commonly used MLB materials. Variation of properties with fiber volume fraction, and nonlinear behavior due to matrix nonlinearity/progressive damage in the transverse yarn are studied using this model. These studies provide valuable insights into MLB property variabilities which, in turn, can cause variations in PTH fatigue life predictions.