Microstructure of combined electroless and galvanic deposits on roll annealed copper foils and copper single crystals

Abstract

The production of highly flexible printed circuit boards requires copper plating on roll annealed (RA) Cu foils with strong (001) crystallographic orientation, with electroless copper plating followed by galvanic copper plating. Concurrent epitaxial and polycrystalline crystal growth during galvanic plating has to be avoided because it leads to unacceptably rough sample surfaces, with polycrystalline regions protruding. Two electroless plating processes are compared in terms of their interaction with the subsequent galvanic plating step. Plating tests are carried out with RA substrates and (111), (011) and (001) copper single crystals. Crystallite orientation distributions are determined by measuring X-ray diffraction pole figures for the substrates, as well as the substrates with galvanic deposits, electroless deposits and combined electroless and galvanic deposits. One of the electroless processes creates Cu {111} planes parallel to the sample surface, thereby reliably disrupting epitaxy between the substrate surface and the growing galvanic film. Moderate constant stress in the electroless processes enables good mechanical adhesion to the substrate.