Three types of copper substrates, fresh, aged (kept for years in open atmosphere) and acid washed aged, were investigated for the reflow behaviour of a solder using different heating rates. Melting point of the Sn-3.5Ag solder was lowered on the aged Cu substrate. Reduction was found to be higher in high heating rate and declined with the decrease in the heating rate. Melting point was lowered from 221 degrees C to 175 degrees C with the heating rate of 180 degrees C/min, but recovered to 210 degrees C when aged Cu substrate was washed with sulphuric acid. XPS depth profile revealed the presence of Cu2O up to the greater depth in the aged substrate compared to the fresh and acid washed aged substrates. Study showed the relation of reduction in melting point with the depth of Cu2O on the surface of aged Cu substrates. It was proposed that lower dissipation of heat generated in high heating rates by the oxidation of the flux carbon during reduction of high Cu2O amount in aged carbon was responsible for the variations in melting points. (C) 2009 Elsevier B. V. All rights reserved.