From the earliest days of producing Stabilant 22, our customers reported problems with tin plated contacts. Beginning in the early 2000’s, a push began to phase out lead solders. To the extent that electronic manufacturing has adopted lead free solder, more tin is now used. The use of tin plating on connectors continues, especially in low cost (consumer grade) systems that allow for short life cycles. We will discuss mainly the corrosion and wear related concerns with tin. It is also advisable to review some of the extensive literature on tin whiskers - these contribute to short circuit failures, mainly where contacts are closely spaced.

 

Tin remains a concern in most electronic systems. An example of tin plated connectors is the header type (with square pins, on 0.10 or 0.156 inch centers), commonly used to connect stacked PC boards, or mated with wiring harnesses.

 

These remain viable for power connectors, but are considered too noisy and have excessive resistance for small signal use. The selection of a connector from a "standard parts" list for cost effectiveness was one of the engineer’s oldest inducements to bypass the technical arguments that favor gold and other more durable plating materials. Even overdesign for current ratings will not solve all of the problems here.

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Where tin plated connectors are deemed appropriate, the engineer requires some data concerning the manufacturing technique. If the forming process involves stretching of the tin plating rather than the use of a coining technique (wherein the tin flows under pressure), microscopic cracking may take place in the tin coating.

 

During manufacture and in service, the lattice structure of tin changes with temperature (even including phase changes). Stresses can be set up that will induce the plating to spall (crack or flake), detaching from the substrate. While this might occur slowly under normal conditions, wearing is accelerated by insertion/removal cycles – tin is highly susceptible to fretting.

 

A well equipped service group can confirm the extent of tin spalling by having contact surfaces examined by electron microscope. Not only are the flakes of plating usually readily apparent, but the pattern of corrosion on the exposed substrate will sometimes show where the original cracking of the tin plating occurred, revealing stresses that were placed on the plating during manufacturing and assembly.

 

As with most connector failures, corrosive influences and the wearing effects described above have a multiplying effect when combined. For example, in a sulfur rich atmosphere, spalling allows more corrosion. Then, spalling is increased to the point of causing connector failure within a year of being placed in service.