Daily, several million square meters of etched PCBs are manufactured worldwide. The actual amount of copper panels processed will be much greater as todays modern circuits often have more than one copper layer; these are known as multilayer PCBs. Of all the multi-layer boards produced, 99.9999% are produced by chemically etching. The adhesive films used to bond the inner layers (PREPEGS) are designed EXCLUSIVELY for etched inner layers.