FINISHING TREATMENT METHOD OF PRINTED WIRING BOARD, SOFT ETCHING LIQUID, AND PRINTED WIRING BOARD

摘要

PURPOSE: To prevent via hole from being disconnected by performing soft etching treatment using a solution containing soluble chloride and further forming a protection film containing CuCl on the surface of at least a desired part of exposed copper film. CONSTITUTION: A liquid solder resist is applied to both surfaces of a substrate 1 and is hardened and a solder resist 4 is formed on both surfaces of the substrate 1. A via hole 3 is covered with the solder resist 4. Then, the substrate 1 is degreased by an alkali solution or a surface-active agent and is softly etched. Chloride ions are added into the liquid being softly etched. Then, acid washing is made by dilute sulfuric acid and rust-proof treatment is performed by benzotriazol. Chloride ions couple with copper plating, thus forming a protection film 6 consisting of CuCl compound rust-proof film. The protection film 6 suppresses the etching of copper when the soft etching liquid condenses and prevents the via hole from being disconnected.