Warpage of the circuit board will cause the components are not allowed to locate. Board bending in the SMT, THT, the components pin is not neat, it will give the assembly and installation work to bring a lot of difficulties.
You need to drying whether the inner or double-sided board before open the material.
6. Sheet is best not through the mechanical grinding brush, the proposed chemical cleaning; plating using a special fixture to prevent the plate bending folding.