FR4 is made from sheets of Prepreg, which is itself
constructed from fibre glass matting which has been impregnated with the
epoxy resin. A standard 1.6mm circuit board is made up from 8 layers of
Prepreg and the outer copper layers. The Prepreg and outer copper foil
layer are stacked up together and placed into a large press which bonds
all the layers into the final laminate.
The copper foil is made on a slowly rotating stainless steel drum
dipped into a copper plating solution. As the drum turns copper is
electroplated onto the drum, which is then stripped off as the plated
section leaves the solution.
The glass cloth is literally made by weaving fine strands of fibre
glass yarn together. The yarn is in turn made from small threads of
glass twisted together. Its the toughness of the glass in the cloth that
give the laminate it's strength, and also the ability to take the edge
off a steel drill bit in seconds.
The epoxy resin is normally made from ethylene
chlorohydrin [epichlorohydrin] and bisphenol-A. Once made the
resin almost indestructible
apart from high temperatures or strong oxidising solutions.
