Guides / Assembly
Flux and cleaning after soldering
Flux makes good joints — and sometimes needs cleaning off afterward. Which type, and when to wash.
Flux is what lets solder wet and flow; it's the difference between shiny joints and frustration. But different fluxes leave different residues, and whether you clean depends on which you used.
The main types
- ·No-clean — leaves a mild residue that's fine to leave on most boards
- ·Rosin (RMA) — leaves a sticky residue best cleaned off
- ·Water-soluble — very active, but the residue is corrosive and must be washed
When to clean
For no-clean flux on a hobby board you can usually leave it. Clean when the residue interferes with high-impedance circuits, conformal coating or inspection — or whenever you used an aggressive water-soluble flux.
How to clean
Isopropyl alcohol and a brush handles most residues; water-soluble flux needs water (deionized is best) and thorough drying. Watch parts that trap liquid — under QFNs and BGAs, and inside connectors.
Good flux discipline also makes hand-soldering SMD far easier.
Ready to prep a board?
Convert a job for any machine →