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 °C to 175 °C with the heating rate of 180 °C/min, but recovered to 210 °C when aged Cu substrate was washed with sulphuric acid. XPS depth profile revealed the presence of Cu 2 O 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 Cu 2 O 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 Cu 2 O amount in aged carbon was responsible for the variations in melting points.
All Science Journal Classification (ASJC) codes
- Condensed Matter Physics
- Physics and Astronomy(all)
- Surfaces and Interfaces
- Surfaces, Coatings and Films