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There is Tin and there is Tin - Characterisation of Tribological and Electrical Properties of Electroplated Tin Surfaces

Electroplated tin surfaces are one of the most used and wide spread contact surfaces for connectors in fields of electrical connectivity and applications. The current study focused on a detailed characterisation of tribological and electrical properties of different electroplated matt and bright tin surfaces to get a deeper insight to the relation of wear failure mechanisms and electrical contact resistance characteristics. The experiments were carried out with a special in-house developed tribometer with variable sliding path, dynamically changeable normal loads and sliding velocities to simulate the sliding motion of connector contacts during insertion and withdrawal. This setup can not only record the occurring friction forces, but has also the capability to measure the contact resistance during every sliding cycle. In a first step we have determined the influence of normal load, sliding distance and velocity on the contact resistance and the friction force by means of a statistical DoE analysis. Hereby we found, that from an electrical point of view matt tin surfaces have a more stable contact resistance characteristic than bright tin surfaces, but under pure tribological aspects bright tin surfaces excel by initially lower friction force values. In the second step the wear tracks were investigated by means of SEM, EDX and optical 3D-microscopy to clarify which major wear failure mechanisms cause the observed different electrical and tribological properties. Within these investigations we were able to identify tin surface specific wear failure mechanisms which can be brought into correlation to the findings of the DoE analysis and can explain the observed contact resistance characteristics.