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#28- On the Upper Temperature Limit for Tin Connector Contact Surfaces

Abstract: For nearly four decades, the published upper temperature limit for tin contact surfaces has been 60°C. Two potential failure mechanisms have been identified and are discussed in this Materion Technical Materials paper.

  • The first applies to thick deposits and is based on the tin softening at temperature, causing local collapse at the interface with a consequential loss in normal force.
  • The second failure mechanism arises from the consumption of free tin due to intermetallic formation.

As the intermetallic layer grows, the apparent hardness of the tin deposit increases. This higher hardness combined with less free tin to extrude through the surface oxide diminishes metal-to-metal contact.

Automotive Tin Connectors

For both cases, contact resistance will increase. During the discussion on this topic at last year's symposium, it was pointed out that automotive tin connectors are routinely exposed to temperatures in the range of 100 to 125°C. Further, a comment was made that the separable interface had become permanent after exposure to elevated temperature for one week. Connector resistance and withdrawal force were measured after exposure and compared to baseline values. Arhennius plots were used to determine to what degree results demonstrated thermal dependence.