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Flux Effect On Solder Surface Tension

#6296

Flux Effect On Solder Surface Tension | 23 August, 2000

Dr. Lee: Some say flux lowers the surface tension of solder. Others argue against that point. What is the flux mechanism that lets solder move more freely?

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Dr. Ning-Cheng Lee

#6297

Re: Flux Effect On Solder Surface Tension | 23 August, 2000

The surface tension of solder you mentioned should be referred to as interfacial tension between solder and flux. According to Antonow´┐Żs rule, the interfacial tension is the difference in surface tension of molten solder and liquid flux. Since flux always exhibits a positive value in surface tension, the interfacial tension accordingly will always be smaller than the surface tension of solder.

The effects of flux on soldering include (1) lowering interfacial tension of solder so that the solder can spread more readily, (2) eliminating metal oxide (or dross) so that the solder can have intimate contact with base metal, (3) oxidation barrier, and (4) heat transfer medium.

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