Study on various film properties of electroless ultra-thin Ni/Pd/Au plating process for fine Cu pattern

Electroless Ni (3-5μm)/Pd/Au plating processing has been applied to various printed circuit boards (PCB). Recently, microfabrication of Cu patterns on PCB has advanced because of demands for high-performance electronic devices. This plating process must soon be able to provide improved plated film selectivity for fine patterns. For instance, thinning of Ni films and electroless precious metal plating processing without Ni plating have been described for the metallizing of fine patterns. Our earlier reports have described investigations of relations among various surface mounting characteristics and Ni film thicknesses (0.01-5μm) on electroless Ni/Pd/Au plated films. Results confirmed that Ni film thickness of less than 0.1μm must be achieved to obtain a selective plated film without deposition on a resin area. However, various surface mounting properties are thereby degraded. The surface mounting property deterioration occurs because of Cu voids by a displacement reaction on plating processes and because of unevenness of the Au surface morphology. For this study, we developed an electroless ultra-thin Ni/Pd/Au plating process without Pd catalyst treatment to resolve the subjects above and to achieve good selectivity and surface mounting properties. Furthermore, the various surface mounting properties were evaluated on electroless ultra-thin Ni/Pd/Au plated films. Results suggest that ultra-thin Ni/Pd/Au plating processes are applicable as electroless precious metal plating processes for fine Cu patterns. (author)