Gold Embrittlement of Solder Joints

Gold embrittlement of solder joints has been written about for at least four decades [1 – 3]. Nevertheless, gold embrittlement related solder joint failures have been analyzed in this laboratory as recently as July 2009. Gold embrittlement can be avoided by careful solder joint design and knowledge of the causes of this condition. The purpose of this paper is to provide a detailed account of material and process parameters that can lead to gold embrittlement in electronic assemblies. There are a variety of reasons that designers might want to solder to gold or gold plating. One reason is that some designs involve wire bonding and soldering operations on the same assembly. Another reason would be to include gold contact pads (e.g. for dome keypad contacts) or card edge contacts (e.g. PC cards). The wire bond pads or contact pads can be selectively gold plated, but the selective plating process can be expensive. The electronics industry currently recognizes a threshold level for gold that can be dissolved into eutectic tin-lead solder above which the solder is likely to become embrittled. This threshold is ~ 3 wt% gold. It will be shown in the paragraphs below that embrittlement of solder joints can develop at significantly lower bulk gold concentrations.