What it measures
A sample is rinsed with a test solution and the change in conductivity is converted to micrograms of sodium chloride equivalent per square centimetre. It is an overall cleanliness indicator, not a map of where the residue sits.
Sources of contamination
- Flux residue from paste or wave solder
- Handling without gloves
- Plating and mask residues from fabrication
- Wash water that was not fully dried
When to test
Before conformal coating, on high-impedance analogue circuits, and whenever the customer specifies a cleanliness limit. Keep the result with the lot record so a later corrosion complaint can be traced.
