AbstractThe microstructures of soldered joints made on gold using silver or zinc doped Pb–Sn solder have been studied in the scanning electron microscope before and after accelerated aging. Layers of Au–Sn intermetallic compounds form between the unreacted gold and the solder as a result of the diffusion of gold through the product layers. The reaction kinetics has been studied as a function of temperature for the silver doped system and, in the initial stages, was found to be parabolic with an activation energy of (0·86±0·03) eV. This is the same as for joints made using undoped Pb–Sn solder. As in the undoped system, the growth of the product layers subsequently fell below the t1/2dependence and loss of joint strength occurred only some time after all the gold had been converted.MST/1599b