ETCHING BEHAVIORS OF GALVANIC COUPLED METALS IN PCB APPLICATIONS

Abstract

In the PCB industry, Cu is the most commonly used metal for circuit line and pad materials. In this study the etching behavior of Cu in two different cases. First, the etching behavior of Cu when connected with Au was studied. After the wiring process, soft etching is performed to remove the copper oxide layer formed on the circuit or pad. Cu is excessively etched by a galvanic coupling of Au and Cu. Electrochemical evaluation such as open circuit voltage (OCV) and polarization curve in two different solutions were analyzed. Optimum etching conditions in which over etching did not occur even in the galvanic couple of Au and Cu were confirmed. Second, the etching behavior of Cu-Invar-Cu (CIC) was studied. It is one of the core candidate materials to compensate the disadvantages of conventional PCB. In wet etching process, it is difficult to obtain uniform pattern due to different etching rates and etching characteristics of Cu and Invar. The etching rates and etching properties of Cu and Invar in FeCl3 and CuCl2 were compared. Finally, the optimum conditions for uniform patterning were obtained.