Cause of Solder Icicles

Why are we getting solder icicles on some leads after we run boards through our wave solder machine? Where should we look first to change our process?

R. J.

Expert Panel Responses

Since the icicles are appearing on "some leads" and not all of them, the problem is more likely to be thermal rather than chemical. It would be interesting to know which particular leads exhibit this icicling effect. It is likely to be the larger, heavier leads that have not reached thermal equilibrium in the wave. Consequently, upon exiting the wave they tend to cool down to the solder's freezing point before all the liquid solder has drained off, causing the residual solder to form the icicle. The first and simplest thing to check is the conveyor speed. Reducing the speed should improve solder drain-off and minimize or entirely alleviate icicles. If this is not totally successful, increasing the pre-heat and/or wave temperature should help. All changes should be made in small increments.

Harold Hyman
Consultant
VJ Electronix

Harold Hyman has been involved in metallurgical aspects of the electronics industry since the 1950's, and in semiconductor development and engineering for STL, Ediswan & RCA. He later joined HTC, a pioneer of vapor phase soldering and continued industry experience Dynapert, GenRad, Teradyne, SRT and VJ Electronics.

Check boards are being fluxed right first and then check top board preheat is around 100-110C, both these can cause this issue. If both of these are correct make sure the solder dwell time is no longer than 3 seconds or you may be burning off too much flux. Lastly ensure the leads are not too long.

Greg York
Technical Sales Manager
BLT Circuit Services Ltd

Greg York has over thirty two years of service in Electronics industry. York has installed over 600 Lead Free Lines in Europe with Solder and flux systems as well as Technical Support on SMT lines and trouble shooting.

Reader Comment

Thanks for the insight. We've run into this problem with some D-Sub connectors recently with heavy hardware. It does seem related to a cold sink and I've seen evidence of the flux drying out so it's a bit confusing. I'll try some of the suggestions to reduce the icicles and save on touch up.

Steven Lord, Heidenhain Corporation

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