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Stages of a Reflow Profile: Part IV

  • Solder Paste

  • Happy New Year everyone! Typically the new year signals a new beginning, but this post will be concluding our series on reflow profiling by discussing the fourth stage of a reflow profile: the cool-down. The cool down rate of the profile will affect the grain structure of the solder joint. A quick cool down will generally create a tiny grain structure which is shinier and stronger. A steep cool down slope will promote quick solidification of the solder thus mitigating void formation, especially for off-eutectic solders that have a plastic range between the liquidus and the solidus where the solder is a “sludgy” material. Too quick of a cooling slope can threaten a  coefficient of thermal expansion (CTE) mismatch. If the CTE mismatch is too great, added stresses and mechanical fracturing can occur. Too slow of a cool down rate will cause an annealing affect and large solder grain structure for a softer and duller looking joint. Ideally, the cool down slope should be no less than 2°C/s and no greater than 6°C/s, but this can vary based on what the assembly can handle.

    If you have questions about your reflow profile, you can contact me at or anyone else on my team of technical support engineers.