Gold or Tin versus Gold and Tin?

You may have already read about my 50:50:50 rule when it comes to the choice using tin plated surfaces versus gold plated surfaces in connectors. This rule says tin is the more economical solution if you have less than 50 contacts (mating forces), if you can live with 50 mating cycles (contact normal forces), and if you do not expect less than 50 milliohms contact resistance over life time. The higher contact normal forces for tin plated surfaces (>2 Newton end of life) result in higher mating forces which limit the amount of contacts in a given connector and the un-noble tin does have a higher contact resistance, compared to gold or nickel palladium.

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