Creep and relaxation behavior of woven glass/epoxy substrates for multilayer circuit board applications

The creep behavior of a common woven glass/epoxy composite substrate for multilayer circuit board applications was characterized using dynamic mechanical analysis (DMA). The creep compliance was measured in both the warp and fill directions of the composite over a temperature range of 30°C to 155°C. The creep compliance of the neat FR-4 epoxy matrix was also characterized for comparison with the composite response. Master creep curves were obtained for the neat resin and the composite in the warp and fill directions assuming thermorheologically simple behavior and applying the time-temperature superposition principle. The creep data was fit to a Prony series and then converted to relaxation data in the Laplace domain. Micromechanical models were developed to predict the relaxation behavior of the woven glass/epoxy composite from the elastic properties and the geometry of the glass fabric and relaxation behavior of the neat resin. Model predictions were compared with experimental data.