Flux residue caught fire on a board I was testing yesterday

I was bench testing a power supply board from a 2015 Dell Optiplex and a blob of old flux under a capacitor ignited when I hit it with 120V. Smelled like burnt rosin and melted the plastic clip holding the cap down. Has anyone else had flux residue catch fire during a hot test, or am I just using too much of the cheap stuff?

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emery9655mo ago

Seen it happen with old boards that weren't cleaned. That rosin flux can get conductive and gunked up over time. A good scrub with some isopropyl alcohol before you power it up can save you the surprise fire show. Cheap flux definitely doesn't help, it leaves more junk behind.

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michael5194mo ago

You mentioned old rosin flux getting conductive. How conductive are we talking? Like enough to actually short something out, or just enough to get hot and smoke?

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