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LEAD-FREE SPRAY FLUXING FOR WAVE SOLDERING |
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A Simple Lead-Free Spray Fluxing Test for Wave Soldering |
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Process Engineers often ask, "Why is spray fluxing more difficult for lead-free wave soldering?" The answer is simple. Lead-free alloys do not 'wet up' the plated-through holes of circuit boards as well as lead bearing alloys.
For solder joints to properly form, the metal surfaces to be joined - molten solder, component leads and the plated holes of the circuit board - must be completely free of tarnish and oxides. This is the job of flux, but flux can only do its job if it is applied to all metal surfaces. A fluxing system that does not completely penetrate the plated holes of the circuit board will leave some metal surfaces dirty, and solder will not flow over them. |
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Sandwiching thermal fax paper (for alcohol-based fluxes) or pH paper (for water-based fluxes) between two bare circuit boards is an easy and effective method of measuring flux penetration of plated-holes.
To conduct this paper test, start by sandwiching the appropriate paper between two bare circuit boards. It is a good idea to clip or tape the circuit boards together so that they hold the paper firmly. |
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Thermal fax paper cut to size and placed
between two bare circuit boards
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Clip the boards together on each end to
hold the paper firmly in place
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Then run the boards through your fluxing system. Once the boards have passed through, immediately remove them and inspect the paper.
If your fluxing system is working well, the paper will change color where flux has penetrated the holes. |
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Conclusion:
Poor spray fluxing can cost manufacturing companies tens of thousands of dollars per year. Lost production time due to clogging nozzles is often measured in thousands of dollars per hour. Touch up of poor solder joints adds unnecessary maintenance and cleaning, and replacement of corroded parts.
Saving money and improving your competitive edge does not have to come just from the low hanging fruit easily within reach. Take a look at your wave soldering fluxing process. With the advent of lead-free manufacturing, fluxing of circuit boards for wave soldering is more important than ever before. Left unchecked, however, and the costs can be substantial. |
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