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This page on connectors is intended to primarily focus on the separable portion of the connector, or more specifically the contact point. In this regard, the answers are relatively straightforward. The overwhelming majority of connectors has contact platings of either tin or gold over nickel, with the appropriate material and thickness dependent upon the use environment (Design Review) and neither plating system in violation of RoHS directives.

A limited number of connectors use tin/lead plating. This portion is dominated by edge-card connections, which use tin/lead HASL as the plating on the board side. A number of publications have reported that tin plating displays a similar of performance as tin/lead in regard to parametric behavior (contact resistance vs. contact force) and robustness (contact resistance after exposure to fretting conditions, mixed flowing gas (MFG), steam aging).

However, board platings do not have the option of switching to standard tin plating as they are limited to certain specialized plating systems. For board platings, there are primarily four choices:

• Selective gold
• Electroless nickel/immersion gold (ENIG)
• Immersion silver
• Immersion tin

Selective gold is by far the most popular option for edge-card connections and is most likely the option of choice for those companies who need a Pb-free edge-card plating material. ENIG is also a potential option, but comes with the risk of black-pad and should only be used for single-insertion applications due to its very thin gold finish (8-10 microinches).