Method for manufacture of printed circuit boards

A method for manufacturing printed circuit boards comprising the steps of:

• (a) providing a non-conductive substrate having a copper layer on both sides thereof and having through-holes made therein and having surrounding pad surfaces;
• (b) depositing copper on the copper layer and through-hole and surrounding pad surfaces;
• (c) applying a resist image which provides a trace pattern on said copper layer;
• (d) subjecting the resulting substrate to a copper electroplating process to deposit additional copper thickness on all exposed copper surfaces including said trace pattern and said through-hole and surrounding pad surfaces;
• (e) applying a tin or tin-lead alloy etch resist to said exposed copper surfaces;
• (f) removing the imaged material;
• (g) etching away all copper from those areas not protected by said etch resist;
• (h) subjecting said etch resist to the action of a first stripper composition comprising an oxidant for the metals of said etch resist and an acid acceptor for the metal cations so oxidized to leave a thin film of tin smut on said surfaces previously protected by said etch resist;
• (i) subjecting said thin film of tin smut to the action of a second stripper composition comprising an aqueous solution containing a mixture comprising an alkali metal hydroxide and an alkali metal chlorite until said thin film of tin smut has been removed and replaced by a layer of copper oxide;
• and
• (j) thereafter selectively applying a solder mask to at least the said trace pattern.