A high reliability halogen-free flame-retardant dielectric for build-up PWBs

We have developed a highly reliable halogen free (hf) flame-resistant epoxy dielectric for build-up printed wiring boards (PWBs). This material would not generate environmentally hazardous products such as polybrominated dibenzodioxins/furans and hormone disruptive agents like Bisphenol-A and its derivatives. The dielectric is composed of a mixture of a reactive type oligomeric organic phosphate and Al(OH)₃ as the flame retardant, a thermally stable polyaromatic epoxy resin as the main component together with a rubber-modified epoxy, and a flexible phenolic epoxy hardener. High Cu conductor corrosion resistance under high-temperature-humidity-bias conditions has been obtained due to the cross-linkable organic phosphate that would reduce the free phosphate ion content. The polyaromatic epoxy resin, which would prevent over-etching of the resin surface during KMnO ₄ etching process, significantly improved the dielectric adhesion to the Cu conductor. The newly developed dielectric exhibited good thermal properties and mechanical properties (Tg of 155°C) such as high flexibility and shock resistance that are very essential in mobile electronic devices like hand phones and laptop-PCs. This material may also have potential usage in high-density packaging