Barrier Layers Against Diffusion

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Abstract
Tests have been carried out on copper and brass substrates which have been electroplated with a number of different barrier layers and then with an excess of matt tin. These samples have been heat treated to simulate accelerated storage and operation periods and observations made on the resulting intermetallic compound layers between the substrate and the tin coating. The results indicate the suitability of each barrier layer for altering the rate of growth of substrate-tin intermetallics and also the ability of the barrier to inhibit the diffusion of, specifically, zinc to the surface of the coating. On the basis of lowest barrier/coating reaction rates, iron appears by far the best choice for a barrier layer.