5 Best Practices for Cleaning High Reliability PCBs
Quick Answer
The 5 best practices for aerosol PCB cleaning: (1) use the straw attachment for controlled, targeted solvent delivery under components; (2) address all corners and sides of contaminated components — flux dams form in corners first; (3) spray angle (30°, 45°, or 60°) matters less than direction — angle toward the component to drive solvent under it, then angle away to push residues out; (4) avoid handheld brushes and foam swabs — they spread partially solvated flux and leave white residues; (5) a final rinse is required — without it, solvated flux residues are relocated rather than removed, causing ionic contamination and field failures. For high-reliability PCBs, skipping the final rinse is the most common cause of post-cleaning ionic contamination failures.
Aerosol cleaning introduces a continuous supply of clean, unused solvent throughout the entire bench cleaning process of printed circuit boards (PCBs). Aerosol cleaning prevents the introduction of new contaminants. This article examines the role that different variables play in aerosol cleaning and offers guidelines to improve an aerosol cleaning process.For a full overview of electronics cleaning chemicals and solvents at MTE Solutions, visit our Electronics Cleaning Chemicals & Solvents resource hub.
Techspray’s G3 Flux Remover (part #1631-16S) aerosol was used for benchtop removal of the flux. Board cleanliness was determined by visual inspection under 64X magnification.1. Use a Straw Attachment for Greater Control and Less Waste
The straw attachment is the single most impactful technique improvement for aerosol PCB cleaning. It allows controlled spray delivery directly under components, eliminating excessive solvent waste on surrounding areas. Without the straw, much of the solvent is wasted on surrounding areas and very little travels under the component where flux residues accumulate.
2. Spray Techniques for Effective Cleaning Under Components
Best results were obtained when both corners and sides of each contaminated component were addressed. Directing solvent into the corners first is critical — flux dams form in corners and block solvent from reaching the center of the component. The more open channels available, the greater the opportunity for flux to be exposed to solvent.
The choice to use an oscillating or stationary spray depends on component size. For small components, a stationary spray is sufficient; for larger components, an oscillating spray across each side produces cleaner results.
3. How Spray Angle Affects Cleaning Efficiency
An exact straw angle of 30°, 45°, or 60° to the board had no measurable impact on cleanliness. Direction matters more than angle — spray close to the board at an angle that guides the solvent under the component to remove residues, then spray from above angling outward along the edges to push residues away from the board.
4. The Right and Wrong Ways to Use Cleaning Tools
Handheld brushes and foam swabs left boards looking dirtier than before cleaning — they spread partially solvated flux around components which then dried, leaving white residues. Foam swabs became flimsy when saturated with aggressive solvents and were easily torn. Brush attachments produced better results than handheld tools due to the constant supply of virgin solvent, but did not match aerosol-only cleaning. Without the force of an aerosol spray, residues under components are unlikely to be fully pushed out.
5. A Final Rinse Is Required
The final rinse is a necessary step — without it, solvated flux residues are relocated rather than removed. This ensures that all solvated flux residues removed from under and around components flow off the board completely. For disposable electronic devices assembled with no-clean flux, an overall rinse may be sufficient. For high-reliability applications, skipping the final rinse is the most common cause of post-cleaning ionic contamination failures that pass functional test but cause field failures.
Frequently Asked Questions About PCB Cleaning
Is no-clean flux truly no-clean for high-reliability PCBs?
No — no-clean flux is not truly no-clean in high-reliability applications. The residues are less aggressive than activated flux, but they still contain ionic compounds that can cause leakage currents, electrochemical migration, and corrosion under humid operating conditions. For medical, military, aerospace, and other high-reliability applications, no-clean flux residues must be cleaned. IPC standards (J-STD-001 and IPC-A-610) require cleaning for Class 3 high-reliability assemblies regardless of flux type.
What is the best solvent for removing rosin flux from PCBs?
For rosin flux removal, engineered flux removers like Techspray G3 are preferred over IPA alone because they are specifically formulated to dissolve rosin and resin flux residues. IPA is effective for light flux residues but may not fully dissolve heavy rosin deposits. For water-soluble flux, deionized water rinse is required — IPA and solvent-based cleaners are not effective for water-soluble flux residues. Always match the cleaner to the flux chemistry used in the assembly process.
How do you verify that a PCB is clean after cleaning?
PCB cleanliness can be verified by visual inspection under magnification (64X or higher) for visible residues, ROSE (Resistivity of Solvent Extract) testing for ionic contamination, and SIR (Surface Insulation Resistance) testing for electrical cleanliness. Visual inspection alone is insufficient for high-reliability applications — ionic contamination is invisible to the naked eye. ROSE testing measures the total ionic content of the board and is the most common production cleanliness verification method.
What PCB cleaning products does MTE Solutions carry?
MTE Solutions carries PCB cleaning products from Techspray and Chemtronics including aerosol flux removers (Techspray G3, Chemtronics Flux-Off), IPA cleaners, precision cleaning wipes, and board cleaning brushes. Techspray G3 is specifically formulated for rosin and no-clean flux removal and is available in aerosol format with straw attachment for precision cleaning under components.
Purchase Techspray’s G3 Flux Remover (part #1631-16S)
Courtesy of TechSpray
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