I need your ideas on how to test flux!

25 May 2022

Bucket of Flux Paste

I have been thinking about an episode that compares different types of flux. Primarily I want to compare rosen, water-soluble, and no clean.

I need your help with at least two aspects.

First, what to cover. The two key areas I am thinking about are how effective are each and how difficult are they to clean? Are there any other areas we should explore?

Second, how to do the testing. My thought was to sand the finish off some scrap PCBs and expose them to moisture to generate some corrosion. Is there another way to simulate joints that require cleaning? Maybe an additional test needs to be soldering new components/PCBs for comparison?

Ultimately, I can solder parts to those PCBs and then compare the resulting solder joints with a microscope.

I'm open to the community's thoughts on what to test and how. So let me know what you think!

Top Comments

dougw over 3 years ago

I don't know exactly how to test this but we recently had a case where no-clean flux became slightly conductive, causing big issues. presumably it was from moisture absorption. It was very unexpected but repeatable.

It probably isn't a fair test, but you could try soldering to aluminum - flux is definitely important for this application
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dougw over 3 years ago in reply to baldengineer

I don't mind the smell, but I am allergic to the fumes - flash fever, non-stop sneezing etc.

Newer flux causes milder symptoms. The fumes definitely have a toxic cocktail of chemicals, although probably not at immediately dangerous levels.
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shabaz over 3 years ago

Hi!

Regarding "Maybe an additional test needs to be soldering new components/PCBs for comparison?" it could be worth showing how to prepare old components, i.e. clean the leads (sandpaper would be the 'keeping it real' method ; ) or those fiberglass pens etc). However, also there could be an explanation why old stock is not always a good idea (e.g. connectors can oxidise/corrode on the mating surfaces, so no matter how much flux is used, the connector can still be unusable), this might also apply to IC sockets.

Regarding cleaning flux, for home use at least, I get great results with just isopropyl alcohol, a brush (this brush is excellent, unlike others it is very stiff) and then mop up the flux and IPA with Bemcot M1 or M3 wipes. Visibly the result is spotless, perhaps not the same as production-grade chemicals of course. MG Chemicals 70/30 wipes are also excellent, but they are more expensive. A bottle of 99% IPA and some packs of Bemcot wipes is cheaper.
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baldengineer over 3 years ago in reply to wolfgangfriedrich

My favorite datasheet is for SMD 291. It says “Has a pleasant odor.” And, I have to agree.
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wolfgangfriedrich over 3 years ago

There has to be a smell test. It will be highly subjective, but I, for one, love the smell of hot rosin flux.

If you think it is a health risk, don't try this at home.
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