Viscoelastic response of woven composite substrates

Micromechanical models are developed to predict the time and temperature dependent response of woven composite substrates used in multilayer printed circuit boards. In the first part of this study, the elastic-viscoelastic correspondence principle is applied to previously reported elastic micromechanical models. The time-dependent creep compliance of a particular composite substrate (7628 style fabric) is predicted and compared with experimental measurements. Several deficiencies and possible modifications to the analytical models are identified. In the second part, a finite element model is adopted to examine the influence of boundary conditions and relevant matrix properties on the composite viscoelastic response. Parametric studies reveal the importance of shifts in the relaxation spectrum local to the matrix in the high volume fraction fiber bundles and the need to account for time-dependent Poisson's ratio of the matrix.