The right PCB cleaning solution depends on what is on the board: flux residue needs a flux-dissolving PCB cleaner (high-purity isopropyl alcohol works for light jobs), dust needs dry removal first, and dirty or oxidised switches and connectors need a contact cleaner. In every case the board should be unpowered and fully dry before it is switched back on.
First, identify the dirt
| What you see | What it usually is | What to use |
|---|
| Sticky, brown or white residue around solder joints | Flux residue | PCB cleaner / flux remover, or high-purity IPA for small areas |
| Grey fluff, loose powder | Dust | Soft brush and dry air first; solvent only if it is oily |
| Crackle, intermittent contact in a switch, relay or connector | Dirt or oxidation on contacts | Contact cleaner, equipment switched off |
| Oil, thermal paste, fingerprints before coating | Surface contamination | PCB cleaner, then dry fully |
| Old conformal coating to strip | Cured coating | Coating remover / thinner |
Flux residue after soldering
Flux residue is what is left after soldering, and it can be sticky or white. Left on a board, it can attract moisture and dirt, and if you coat over it the coating can lift.
Protektor PCB Cleaner (SKU 3400) is listed to remove light flux residue after wave soldering, thin oils, thermal paste, ink and grime, and to dissolve misprinted solder paste. It is described as residue-free and non-ionic. See flux residue on PCB.
What about PCB cleaning alcohol (IPA)?
Isopropyl alcohol is a common bench cleaner for flux because it dissolves many flux types and evaporates quickly. Use high-purity IPA (99% or similar), not 70% rubbing alcohol, which contains a lot of water and dries slower. Scrub gently with an ESD-safe brush and wipe or blot the dissolved residue away; if you just let it evaporate, the flux is redeposited as a white film. IPA is flammable.
For production boards, or for boards that will be conformal coated, a dedicated PCB cleaner is the more consistent choice.
Dust on a PCB
Dust is usually dry. Remove it first with a soft anti-static brush and clean, dry air. Using solvent on a dusty board just turns the dust into mud. Use a cleaner only if the dust is stuck in oil or grease.
Dead switches, relays and connectors
Crackling pots, unreliable switches and intermittent connectors are contact problems, not board problems.
- Electrical Contact Cleaner (SKU 3201) is listed for dust, light oils, fingerprints and flux traces on contacts, control assemblies and connectors. Its directions say not to use it on energised equipment or sensitive electronic equipment, and it uses a butane propellant. For boards, use the PCB cleaner instead.
- Non Flammable Contact Cleaner (SKU 3211) is listed for dirt, oil, flux and oxidation, including ECU connectors and fuse boxes. Test it first on PC, ABS, acrylic, painted surfaces and rubber gaskets.
Even where a product claims to be safe on live equipment, we advise switching off and isolating before cleaning. See dirty or oxidised switches and connectors.
Cleaning before conformal coating
Coating over oil, flux or dust causes de-wetting, bubbles and lifting. Clean with a PCB cleaner, let the board dry fully, then coat. Protektor Conformal Coating (SKU 3100) is the coating we list for moisture protection. See cleaning PCBs before coating.
Safety: PCB cleaners, IPA and contact cleaners are solvents, mostly in pressurised cans. Work with ventilation, keep away from sparks, flames and hot soldering irons, keep the equipment unpowered, and follow the label and SDS.
When to ask an expert
- Your customer specifies an ionic contamination or cleanliness test.
- Contacts are burnt or pitted: cleaning will not fix damage; replace the part.
- Coating adhesion keeps failing even after cleaning.
- You are cleaning medical, automotive or safety-critical electronics.
Send us a photo of the board and the residue; we will tell you what we would use.
FAQ
What is the best PCB cleaning solution for flux?
A dedicated PCB cleaner or flux remover. For small repairs, high-purity isopropyl alcohol with a brush works for many fluxes. Wipe the dissolved residue away rather than letting it dry back on.
Can I use alcohol to clean a PCB?
Yes, use high-purity IPA (around 99%), with the board unpowered. Avoid 70% rubbing alcohol because of its water content.
Is a PCB cleaning spray better than IPA?
For production work and before conformal coating, a dedicated spray cleaner is more consistent and can reach under components. For a quick bench touch-up, IPA is fine.
Can I use contact cleaner on a PCB?
Some are listed for PCBs, but read the directions. SKU 3201's directions exclude sensitive electronic equipment, so for boards use a PCB cleaner.