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How to clean the PCB circuit board

How to clean the PCB circuit board

I have been assembling a lot of USB PCB boards recently, which reminded me of the best way to clean them after assembly. I used "dirty" flux during assembly work, so theoretically I don't have to clean it up, but if I don't, it will leave an ugly sticky mess. Unfortunately, the black solder mask of the retro USB board seems to highlight flux residue more than other colors. I have also recently started to use gel instead of flux pen in the syringe, it is more viscous and leaves more residue. So good cleaning is more important than ever.

In the past, my standard cleaning method was to use ordinary cotton swabs with 99% isopropyl alcohol. It can dissolve flux residues, but this cotton swab can easily trip over the sharp corners of the part, quickly turn into pieces, and leave tiny cotton fibers everywhere. Sponge cotton swabs and cloth-headed cotton swabs are used in the back. These cotton swabs are basically designed for industrial use. In any case, the packaging and winding of cotton are tighter than ordinary cotton swabs, and they are "low lint", and at the same time show superior abrasion resistance and cleanliness performance, and can be wiped repeatedly. It helps to reduce shreds and stray cotton fibers, but it cannot eliminate them completely.

As you can see here, isopropanol also leaves residues that look unattractive. Its visibility largely depends on the angle of light, and I deliberately chose the worst angle photo. I'm not sure if this residue really comes from alcohol, or if it is a residue dissolved in alcohol, but whether there are stripes on the PCB circuit board when it dries. I found that I need to wait until it dries, then use another dry cotton swab to wipe the dry area and remove the streaks. The final result is still not perfect, although it is very good. But the entire cleaning process can be very time-consuming, requiring several minutes for each circuit board.

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