Behaviors of polymeric materials and their effects on high density PWB

In this study, properties of some selected, representative high density int erconnect (HDI) materials (dielectric and solder mask), including dimension al stability (thermal and chemical),::tensile behaviors, and fracture tough ness have been investigated. Experimental results show that glass transitio n temperature of materials cured with the manufacturer recommended schedule did not reach their ultimate, alleged published values, indicating that fu rther curing is needed. Most HDI materials are brittle at room temperature with a low strength and low elongation at:failure. It has been found that t he resistance to crack propagation of HDI materials is much lower than that of polymer thin films, such as Kapton, widely used in electronic products. It has also been observed that stress-strain behaviors of partially cured materials and fully cured materials are very close at room temperature but very different at higher temperatures, Finite element analyses, however, in dicate that low fracture toughness of HDI materials will not be major cause if cracks are observed in the thermal cycling of HDI boards. Rather, it wo uld be due to combined contribution from low strain-at-failure, strong visc oelasticity, and low fracture toughness.