Electroless deposition of tin onto copper surface has been studied by means of electrochemistry, X-ray fluorescence spectrometry, and theoretical Hartree-Fock methods. There are two processes in series involved in the hypophosphite-type immersion tin reaction, based on the analysis of the immersion tin potential curves and the structure of the deposits. The first displacement process is significantly affected by the complexing agents of cuprous and the concentration of SnSO4, mainly due to the formation of Cu-Sn alloy and a thinner tin layer. The second process is attributed to the stannous ion reduction by hypophosphite at higher temperatures. (c) 2006 The Electrochemical Society.