Preparation of tin diffusion coatings on copper

Processes have been developed to produce single-phase copper–tin coatings of either the terminal solid solution or the Cu₃Sn (ε) intermetallic compound on a copper substrate by a method not involving electrolytic codeposit ion. A ‘precoating’ was deposited which consisted generally of one or more pairs of alternate 1 μ thick electroplated layers of tin and copper. Heat treatments were chosen to promote diffusion between molten tin and solid copper. The preferred technique was to use a copper top layer as part of the precoating to prevent dewetting of the tin. The alternate-layer method significantly reduced the time required to produce 10 μm coatings of Cu₃Sn by partitioning the tin into several separate diffusion systems.