SMTA International Conference Proceedings

Corrosion Mechanisms of Lead-Free PCB Surface Finishes in Corrosive Environments

Authors: C. Xu, W.D. Reents, Jr., D.A. Fleming, J.P. Franey, G.E. Derkits Jr., P. Ahern, B. Wright, K. Demirkan, R. L. Opila, K. Hannigan, M. Reid, J. Punch, and M.N. Collins
Company: Alcatel-Lucent, University of Delaware, and Stokes Institute, University of Limerick
Date Published: 10/14/2012   Conference: SMTA International

Abstract: As the electronics industry moves toward lead-free and high density circuit boards, the widely used PCB finish, tin-lead Hot Air Solder Level (HASL), is being increasingly replaced with lead-free and coplanar PCB finishes such as Immersion Silver (ImAg), Organic Solderability Preservative (OSP), Electroless Nickel/Immersion Gold (ENIG), Immersion Tin (ImSn) and Electroless Nickel/Electroless Palladium/Immersion Gold (ENEPIG). Along with this transition, corrosion resistance is being reduced and product failure occurrences due to corrosion of lead-free PCB finishes have been reported.

In this work, corrosion products of lead-free PCB finishes in a mixed flowing gas (MFG) environment, designed to mimic the harshest ambient conditions found in the current worldwide marketplace, were characterized using optical microscopy, scanning Auger microscopy (SAM), Scanning Electron Microscopy/Energy Dispersive Spectroscopy (SEM/EDS), X-ray Diffraction (XRD) and Focused Ion Beam/Energy Dispersive Spectroscopy (FIB/EDS). The composition and structure of corrosion products were determined, providing insight into the corrosion mechanism for each finish studied in this work. Methods for improving corrosion resistance of the lead-free PCB finishes will be discussed in light of the experimental finding in this work. It is hoped that this understanding will benefit the development of more corrosion resistant surface finishes and optimization of current commercially available finishes.

Key Words: 

corrosion mechanism, surface finish, mixed flowing gas

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