FR 4 is today’s standard board material for double sided and multi-layer industrial pcb’s. They are manufactured from woven glass fiber mats soaked in epoxy resin. Its mechanical strength is very high. The designation FR 4 encompasses, though, encompasses a large group of basic materials, which can differ in many of their characteristics. Exemplary for these differences are the glass transition point, delamination temperature, coefficient of expansion in the z-direction, and some electrical characteristics.