Influence of Cleaning and Soft Etching for Electroless Palladium/Gold Plating on Copper Fine Pattern

Abstract

Electroless nickel/gold plating and electroless nickel/palladium/gold plating processing have been applied widely to copper patterns as a surface finishing treatment for electronic devices. Recently, miniaturization of copper patterns has advanced to increase the functionality of electronic devices. Conventional electroless nickel plating processing applied to fine copper patterns causes nickel growth in the lateral direction. As a result, the copper pattern distance narrows, which might cause short circuits. To resolve this difficulty, electroless palladium plating on copper has been investigated. This study specifically examined pretreatment processes involving cleaning and soft etching. Results show that the wire bonding characteristics on the electroless palladium/gold plated film differed remarkably depending on the selection of the pretreatment solution used for cleaning and soft etching. Particularly, using a neutral cleaner and a thiol type soft etching solution suppressed dissolution of the copper during the palladium catalyst treatment. Results show that the possibility of obtaining a palladium plated film with fewer pinholes and voids. For electroless palladium /gold plating processing, results show that the soft etching step and the selection of the pretreatment solution used in the cleaning step are important.