How to choose a cleaning process for electronic boards?

The most common reflex is to start with the machine. It should be the other way round: first define the contaminant to be removed and the expected cleanliness level, then deduce the process, and only then the equipment. This guide lays out the method.

Start from the contaminant, not the machine

An assembled board rarely carries just one type of soil. Depending on the assembly process, you will find flux residues (no-clean or water-soluble), unreflowed solder paste, ionic traces, and sometimes residues of conformal coating or protective gel. Each behaves differently when exposed to chemistry, temperature and mechanical agitation.

Identify the contaminant first

• Type of flux used (no-clean, water-soluble, rosin) and its data sheet.
• Component density and the presence of low-standoff packages (BGA, QFN).
• Sensitivity of components to water, temperature and ultrasonics.
• Final cleanliness requirement: cosmetic, functional, or standards-based (ionic residues).

Criteria for choosing the process

Four families of processes cover most cases in aqueous cleaning. The table below summarises their typical areas of use — always to be confirmed by a trial on your actual parts.

Usage guidelines (to be validated by trial)

Measure cleanliness, don't guess it

A board that is “clean to the eye” may retain ionic residues that degrade long-term reliability (leakage currents, corrosion, dendrites). Cleanliness must be assessed by an objective measurement — extract resistivity, localised measurements — and tracked over time, not simply observed visually.

Build traceability in from the start

In demanding electronics, the cleaning process must be documented like a production step: cycle parameters, lots, operator, inspection results. Planning for traceability when choosing the machine avoids having to add it afterwards.