Consumption of Cu pad during multiple reflows of Ni-doped SnAgCu solder

Abstract

Abstract The effects of solder volume and the number of reflows on the Cu consumption rate were studied. Nickel-doped Sn3Ag0.5Cu0.02Ni solder balls of different diameters (300, 400, 600 and 760 μm in diameter) were reflowed over Cu soldering pads with an opening of 600 μm in diameter. The reflow profile had a peak temperature of 235 ± 2°C and a 90 s duration during which the solder was molten. The nominal ramp rate and cooling rate were both 1.5 K s−1. The first reflow consumed the largest amount of Cu, and the subsequent reflows only consumed marginally more Cu. It was argued that the solder joints became saturated with Cu during the first reflow so that during the subsequent reflows the Cu substrates were consumed at markedly reduced rates. The Cu consumption increased with the diameter of the solder balls. This was because a larger amount of Cu was needed in order to saturate a solder joint with a larger solder volume. The doping of Ni did not change the Cu consumption rate despite the fact that the am...