Rant: Took me 10 years to figure out I was cleaning flux wrong

I used to scrub boards with isopropyl alcohol and a toothbrush after soldering, thinking that was good enough. Then last month I was reworking a 20-year-old audio mixer from a local repair shop, and I noticed this white crusty residue under a chip that was causing intermittent noise. I asked the old-timer I share bench space with, and he just laughed and said stop using 70% isopropyl and switch to 91% or better yet 99%. I felt like an idiot because I'd been using the cheap drugstore stuff for a decade, and the water content in the 70% was leaving minerals behind that would eventually corrode stuff. Switched to 99% last week and a good ultrasonic cleaner with proper flux remover, and now my boards come out spotless. Anyone else have a moment where you realized you were making a basic mistake for years?

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1 Comment

terryrobinson1mo ago

A 20 year old audio mixer with a crusty residue under a chip is exactly the proof I need that you were probably fine before lol. The old timer laughed at you but that white stuff is usually just rosin flux that didn't get fully cleaned off, not mineral deposits from water. I've been using 70% isopropyl for like 15 years on everything from guitar pedals to vintage synths and never had corrosion issues. The ultrasonic cleaner with special flux remover sounds like overkill for hobby work, and honestly I think you got upsold on a problem that didn't really exist for most people.