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I finally saw what cheap flux does to a board after 6 months | Electronics Repairers - Opinions Matter

I finally saw what cheap flux does to a board after 6 months

A guy brought in his amp last week that I'd fixed half a year ago, and the joints had turned into a corroded mess from the flux I used. Grabbed a bottle of Kester from the shop now, has anyone else had a repair come back to bite them like this?

3 comments

3 Comments

miles5813mo ago

Are you sure the cheap flux is the only problem here though? I gotta respectfully push back on @shah.ben's advice a bit because scrubbing with drugstore isopropyl has let me down before. The 91% stuff still has water in it that can sit under parts and cause corrosion later if you don't bake the board dry. I've used the cheap flux myself and it did the same green crusty mess, but switching to Kester RMA flux and using 99% alcohol with a proper flux remover brush made a world of difference for me in humid weather. No-clean flux is definitely a lie for sure, but the alcohol quality matters just as much as the flux brand in my experience.

robert_rodriguez663mo ago

Actually that cheap flux might not be your only problem. Most people don't realize that if you don't clean the board properly after soldering, even good flux can cause issues down the road. The Kester stuff is definitely way better quality though, I switched to it years ago and haven't looked back. Had a similar thing happen with a guitar pedal where I got lazy and left some no-clean flux residue, and it started getting that green crusty stuff after a few months. Since you already fixed it once, just make sure you give the board a good scrub with some isopropyl alcohol after you redo those joints and you should be good for way longer.

shah.ben3mo ago

Got a bottle of 91% isopropyl from the drugstore and a cheap toothbrush works fine for scrubbing boards. I actually had the same green crusty stuff show up on a thermostat board I wired up last year. The no-clean flux claim is a lie in my experience, especially if you live anywhere with humidity like I do. Give it a good scrub with the alcohol and a toothbrush, let it dry fully, then redo those joints and you'll be set for years.