ÿþ<html><head> <title>The Influence of H2S Exposure on Immersion-Silver-Finished PCBs Under Mixed-Flow Gas Testing</title></head> <body bgcolor="#ffffff"> <center> <i>IEEE Transactions on Device and Materials Reliability, Vol.10, No.1, pp.71-81, March 2010 </i> <br><h2>The Influence of H2S Exposure on Immersion-Silver-Finished PCBs Under Mixed-Flow Gas Testing</h2> <p><strong>Shunong Zhang and Rui Kang</strong><br> Department of Systems Engineering of Engineering Technology <br> Beijing University of Aeronautics and Astronautics<br> Beijing 100191, China</p> <p><strong>Michael Osterman, <em>Member, IEEE</em> and Anshul Shrivastava</strong><br> Center for Advanced Life Cycle Engineering <br> Department of Mechanical Engineering <br> University of Maryland <br> College Park, MD 20742 USA</p> <p><strong>Michael G. Pecht, <em>Fellow, IEEE</em></strong><em></em><br> Department of Electronics Engineering <br> City University of Hong Kong, <br> Kowloon, Hong Kong <br> and <br> Center for Advanced Life Cycle Engineering<br> Electronics Products and Systems Center<br> University of Maryland <br> College Park, MD 20742 USA</p> <p>&nbsp;</p> </center> <p><b>Abstract:</b></p> <p>This study focuses on the corrosion of immersion silver (ImAg)-finished copper land patterns on printed circuit boards (PCBs) under H<sub>2</sub>S exposure. Eight test conditions were examined with varying levels of H<sub>2</sub>S, temperature, relative humidity, and exposure time. The results indicated both direct chemicalreaction corrosion and electrode-reaction corrosion, particularly galvanic corrosion. H<sub>2</sub>S gas was a stronger driving force for corrosion on ImAg-finished PCBs than SO<sub>2</sub> gas. Temperature had a significant influence on ImAg-finished surface PCBs. Tests found extensive corrosion on ImAg-finished PCBs at 40&deg;C, even in very low humidity. On ImAg-finished surfaces, the corrosion was nonuniform during the early period of exposure, with the corrosion modes being mainly pitting, open mouth, and particles. The corrosion products at this early stage mainly included Cu<sub>2</sub>O and Ag<sub>2</sub>S. As time progressed, the corrosion products mainly included Ag<sub>2</sub>S, Cu<sub>2</sub>S, CuS, and CuO. These formed a passive film on the surface. ImAg-finished PCBs are vulnerable to H<sub>2</sub>S gas; nonuniform severe corrosion was found to occur at defects on the ImAg surfaces. The mixed-flow gas test produced creep corrosion on ImAg-finished PCBs using only H<sub>2</sub>S gas. Dendrite corrosion products growing from an edge with a solder mask were generally longer than those growing from an edge without a solder mask. The corrosion products of these dendrites mainly included Cu<sub>2</sub>S or CuS. <p><strong>Index Terms </strong>&mdash; Corrosion, H<sub>2</sub>S environment, immersion silver (ImAg) printed circuit board (PCB), mixed flow gas (MFG) test.<p><a href="../../fulltext/2010/H2SExposure.pdf">Complete article</a> is available to CALCE Consortium Members.</p> <p><font size="-2"><font color="red">&copy; IEEE. Personal use of this material is permitted. However, permission to reprint/republish this material for advertising or promotional purposes or for creating new collective works for resale or redistribution to servers or lists, or to reuse any copyrighted component of this work in other works must be obtained from the IEEE.</font></font></p> <hr><br> <center> [<a href="http://www.calce.umd.edu">Home Page</a>] [<a href="../../../articles">Articles Page</a>] </center> <center> <font size="-1">Copyright &copy; 2010 by CALCE and the University of Maryland, All Rights Reserved </font> </center> </body></html>