The implementation of lead free solder has forced solder suppliers, component manufacturers, board providers, reflow process engineers and standards groups to look at all aspects of the reflow profile. One area that is receiving increased attention is the cooling rate. Some studies show that the shear strength of tin-silver-copper (SAC) solder is slightly lower than eutectic lead solder and that smaller grains obtained by faster cooling can regain some of the strength. On the other hand, large BGAs advocate slower cooling rates to minimize shearing.

The affect of these studies has placed additional stress on reflow process engineer’s being asked to produce profiles near the edges of and beyond the capability of some reflow ovens. This paper will cover the control parameters and modifications that can be made to reflow ovens to explore increased and decreased cooling rates.

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