Halogen-free flame-retardant plastics for electronic applications

In order to meet international standards, printed circuit board (PCB) base materials have to be flame-retardant according to the UL 94V specification. Up to now this has been achieved with FR4 materials by using brominated aromatic components. FR4 materials are glass epoxy based and are by far most prevalent in PCB production. Unfortunately, in the case of fire or smoldering, these materials evolve highly corrosive, and, under unfavorable conditions, even highly toxic decomposition products. In the search for flame retardancy without the use of bromine, the effect of different structural elements on the burning behavior of cured resins has been investigated. As a result of these investigations an epoxy resin was developed that contains tailor-made N- and P-containing constituents that form flame-retardant structures during processing and curing of the material. The new material meets all requirements for printed circuit boards and can be processed without any need to modify established technologies. Analytical and ecotoxicological investigations of the combustion products of the new material show that they are comparable with those of wood from the beech tree. PCBs and electronic assemblies manufactured therefrom successfully passed all functional tests. The base materials recently became commercially available.