How to clean ESD PCB racks without ruining them

Line racks pick up flux from boards loaded while still warm, plus fine glass dust from depaneling. Add solder balls, fingerprints and the glue from peeled labels, and each of those rides onto the next board that goes into the slot.

Brush and vacuum first

The risk in cleaning is damaging the ESD surface, so start gentle. Most of what collects in a rack is loose, so a soft brush and a vacuum get most of it. Use an ESD-safe vacuum. An ordinary shop vacuum builds charge on its hose and nozzle, and you'd be running that nozzle along every slot.

Compressed air mostly moves dust onto the next rack or the bench, and a fast stream of dry air generates charge of its own. Stick with the vacuum.

Wiping

For flux and fingerprints, wipe with isopropyl alcohol on a lint-free cloth and let it flash off completely before loading boards. IPA is fine on carbon-loaded racks, which conduct all the way through. If a rack relies on a topical antistatic treatment, IPA can wipe the treatment off, so find out which kind you've got first.

Check the rack material before trying anything stronger. Some engineering plastics crack or craze when aggressive solvents reach areas already under stress, like slot roots and molded corners, and the cracks can take days to appear. If the data sheet doesn't list a solvent as compatible, test it on a spare rack.

Products to keep away from racks

Silicone sprays and plastic protectants leave a thin film that can insulate the surface. Silicone that transfers onto boards also causes solderability and coating adhesion problems, and it's very hard to trace back to a rack once it happens.

Household cleaners often leave surfactant residue, which shouldn't be anywhere near assemblies. Abrasive pads remove topical treatments and coatings wherever they scrub, and even on carbon-loaded plastic they leave scratched slots that catch board edges.

If you dry racks in an oven, keep it well below the rack's temperature rating. On magazine racks, don't put silicone grease on the lead screws or guides. Use the lubricant the maintenance instructions specify, and not much of it.

Measuring after you clean

A cleaning method can leave a film nobody sees, so take surface resistance readings on a few racks before and after. A rack that was in range before cleaning and out of range after has picked up a film, and the cleaner or the method needs changing. Check your electrodes and test setup against ESD surface resistance explained for PCB racks before you trust a reading.

Clean on the same schedule as those resistance checks. Racks near depaneling and reflow need it more often than racks in a stockroom.

Side panels do wear out, and some racks can't be saved by cleaning. We stock replacement side panels and wear kits for our magazine racks in rack spares.

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