Printed circuit board or PCB is the copper laminate board, which after etching is used for mounting and connecting electronic circuit components. Originally PCBs had holes for component leads, pins, wires, etc. which passed through and were soldered to the copper tracks on the underside. From the 1980s surface mount components have been used increasingly instead of through-hole components. Double-sided or multi-layer boards use plated-through holes, called vias to connect the traces on different layers. The most common PCBs are composed of either FR4 (glass fiber and epoxy), or the cheaper and easier to cut and drill but more brittle SRBP (Synthetic Resin Bonded Paper).