A printed circuit board (PCB) is
composed of extremely thin sheets of conductive copper foil joined to sheets of a dielectric (nonconductive) resin-impregnated material called ‘prepreg.’ The process for making multi-layered printed circuit boards stacks sheets of copper foil and prepreg in a press, heats them to melt the resin in the prepreg, and thereby bonds the layers."
- Johnson & Johnston Assocs. Inc. v. R.E. Serv. Co., 285 F.3d 1046, 1048 (Fed. Cir. 2002) (full-text).