As Flexible PCB supplier china knows that, the hardened photoresist on the copper inner layer protects the traces, vias and other areas of the metal circuit, and the remaining photoresist is removed to expose the bare copper. Etching is then performed to remove unprotected bare copper, leaving the required circuitry. After removing the hardened photoresist, only the copper circuit remains in the inner layer.

Repeat this step for each pair of inner layers until all layers are complete. The next step is to laminate all the inner layers with the epoxy-impregnated fiberglass board, called the “prepreg.” Once the top and bottom of the board are covered by a thin layer of copper foil, the board can be laminated together by heating and pressure. Once laminated, a through-hole is drilled in the plate to prepare for the next etching process.