RESIDUAL STRESSES AND WARPAGE IN CIRCUIT BOARD COMPOSITE LAMINATES.

Residual stresses are introduced in composite laminates during curing as a result of differential thermal expansion of the various plies. Residual stresses coupled with asymmetries in the laminate produce warpage. To study these phenomena, symmetric and asymmetric glass-fabric reinforced laminates were fabricated. The laminate material was fully characterized by determining its physical and mechanical properties at room and elevated temperatures. Thermal strains during curing and subsequent thermal cycling were measured by means of embedded strain gages. Residual stresses were subsequently calculated using the mechanical properties determined before. Warpage for known types of asymmetry was then calculated by means of lamination theory and compared with experimental measurements using a projection moire technique.