Copper foil surfaces with pits have a great influence on the PCB quality, and can cause short circuits or broken circuits in the printing line.

Pits are mainly caused by hard residue in pressing stainless steel, which is mostly made of cured resin powder. The residue is hard to brush away by steel plate cleaner, and uneven surfaces will always be present with repeated use of steel plate.

Due to the pressing stainless steel with electrostatic, stainless steel easily adsorb dust and impurities with poor production environment. These impurities can cause pits on the copper foil surface. Residue resin on the steel plate mainly formed in stack-up unit, and can easily stick to stainless steel by hot pressing.

Copper clad laminate has glue spots on the surface, which is hard to remove and will cause printing lines to short circuit.

• Copper foil has small holes, and glue spots can be easily form on the surface by resin penetration.
• Glue spots are formed on the copper foil surface due to the falling resin from adhesive sheet by improper operation.

We can check whether there is a hole on the copper foil with fluorescent light.