The Growth of Intermetallic Compounds on Common Basis Materials Coated with Tin and Tin-Lead Alloys

SummaryThis paper is the second in a series which reports the results of experiments to determine the rate of compound growth at temperatures below the melting point of tin and tin alloy coatings on various metals and the effect of compounds so formed on the mechanical and physical properties of joints. The present report deals with hard and soft copper, nickel, silver and brass as substrates plated with coatings of tin and tin-lead alloys containing 60%, 30% and 10% tin and also a hot dipped 60/40 tin-lead coating, stored at various controlled temperatures and at room temperature. Growth rate curves have been experimentally determined based on storage times up to nearly 5 years. Activation energies have been calculated from Arrhenius plots and these allow estimations of the rate of compound growth at any temperature intermediate between those studied. The compound layers have been identified and it is shown that lead does not enter into the compound layers and that for brass substrates the two compounds observed contain zinc. With the exception of the nickel basis material, all systems are found to show a fast initial growth rate followed by a region of slower growth rate which obeys classical laws.