Improvement of Corrosion Resistance of Electroless Au/Ni-P Layer using Self-assembled Monolayers of 1-octadecanethiol

• Published in: Hyōmen gijutsu Vol. 63; no. 9; p. 585
• Main Authors: ONO, Kazuhide, KURASHINA, Tadashi, NATORI, Yuta, TAKAHASHI, Koji, NONAGASE, Yuji, KODAMA, Naoki
• Format: Journal Article
• Language: Japanese; English
• Published: Tokyo The Surface Finishing Society of Japan 01.09.2012; Japan Science and Technology Agency
• Subjects: 1-octadecanethiol; Corrosion Resistance; Electroless Gold Deposition; Self-Assembled Monolayer(SAM)
• ISSN: 0915-1869; 1884-3409
• DOI: 10.4139/sfj.63.585

This study was conducted to improve the corrosion resistance of electroless Au/Ni-P layers used in printed wiring boards(PWB) without degrading solder-ball bondability and wire bondability. We examined self-assembled monolayers(SAM) of n-alkanethiols as corrosion inhibitors. The n-alkanethiol adsorption was evaluated using the contact angle of water. Corrosion resistance was evaluated using the salt spray test. Results show that excellent corrosion resistance was obtained for long carbon chains and high concentration. After heat treatment of an Au/Ni-P substrate on which ODT-SAM had been formed, the Au-plated surface was measured using X-ray photoelectron spectroscopy. The diffusion of Ni was less than that obtained with an Au/Ni-P plated substrate on which ODT-SAM had not been formed. Therefore we infer that ODT-SAM functioned to seal pinholes. Apparently, the corrosion resistance in the salt spray test was improved because ODTSAM inhibits contact between salt water and the Ni-plated film. Furthermore, no deterioration of bondability properties was observed when solder-ball bondability and wire bondability were evaluated for an Au/Ni-P substrate on which ODT-SAM had been formed. Therefore, ODT-SAM is inferred as effective to improve the corrosion resistance of electroless Au/Ni-P layers of PWB.