Cupric Chloride-Hydrochloric Acid Microetch Roughening Process and its Applications

摘要

We have developed a cupric chloride-hydrochloric acid based microetchant process. This process provides a unique roughened copper surface, which yields excellent adhesion for both solder mask and dry film photo resist applications. The process also yields excellent solder mask adhesion through subsequent silver, tin and nickel plating post solder mask application. The amount of copper etched using cupric chloride-hydrochloric acid based microetchant is not as high as that seen typically in cupric chloride etching systems. Airborne oxygen is efficient enough to be used as an oxidizer in the system. Hydrochloric acid maintains the proper hydrogen and chloride ion concentrations. The cupric ion maintains itself throughout the process. The chemistry and process are both easily controlled. The process operation is comparable to a mini cupric chloride etcher, whereby copper concentration is maintained by specific gravity and acidity can be controlled by conductivity. It is not necessary to control oxidation-reduction potential, hence the difference as compared to conventional etching processes. This technology provides highly roughened copper surfaces for conventional acid plated copper such as PPR and DC, and standard regular copper clad, which offers great adhesion for solder mask and dry film photo resist. For solder mask applications, it is necessary to produce a rougher topography by controlling micro etching rate at 1.0-1.5 μm/m to get good adhesion between copper surface and solder mask when the final finish is involved in immersion or electroless plating process with tin or nickel. For dry film photo resist applications, the processed copper surface is rough enough to improve the adhesion at micro etching rate below 1.0 μm/m. The copper surface roughness should be controlled within a range to balance the adhesion and resolution when dryfilm photo resist is used for fine line boards.