Influences of Electroless Nickel Film Conditions on Electroless Au/Pd/Ni Wire Bondability

概要

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Electroless Au/Ni plating is intensively applied to high-density printed boards. In this process, local corrosion often occurs between the deposited nickel and the deposited gold. Generally, nickel tends to diffuse from the local corroded areas to the deposited gold surface after thermal treatment due to its strong affinity for oxygen. These areas cause surface mounting failures. Recently, electroless Au/Pd/Ni plating has been actively studied as a substitute for electroless Au/Ni plating because it suppresses the nickel corrosion reaction. In this study, we investigate the influence of the nickel microstructure and the thickness of the palladium and gold on wire bondability. The wire bonding strength is increased with increased palladium and gold film thickness. The deposited nickel microstructures also influence the wire bonding properties after thermal treatment. It was confirmed that good wire bonding properties can be achieved using a nickel film with a layered microstructure rather than a columnar microstructure. From the AES analysis, we confirm that preparation of a uniform layered microstructure of the nickel film is a key factor to keep the gold concentration on the gold film surface after thermal treatment.