Why the Right Electronics Cleaning Will Extend Product (and Human) Life
Cleaning circuit boards and other electronics is an unavoidable fact of life – at least sometimes. Cleaning processes add time, which can affect time-to-market and add costs. But we are all aware of the harmful effects of flux. Skipping the cleaning stage can lead to diminished reliability, performance, and product life as well as more severe problems down the line – like complete product failure. Thankfully, high-quality flux removers like those from Chemtronics and smart techniques can streamline and optimize cleaning.
Skipping the cleaning stage can lead to diminished reliability, performance, and product life as well as more severe problems down the line
To clean or not to clean
Many times, cleaning a PCB comes down to a subjective decision related to its application and reliability. If a disposable product like a computer keyboard fails, no one will lose his or her life. So it’s reasonable to use a no-clean flux and skip the cleaning process altogether. On the other hand, requirements are much more stringent for electronics that drive critical vehicle components/processes, medical devices, or aerospace electronics. In these instances, board failure can lead directly to death.
Medical device (like a pacemaker) cleaning is required after assembly and any subsequent rework, and the process will be thoroughly tested for effectiveness and repeatability. Long-life durable goods fall somewhere in between, with cleaning required but without rigid testing and controls.
Corrosion risks and types
Flux residues left on electronic circuit boards are acidic. If they aren’t removed, residues can draw in ambient moisture from the air and lead to corrosion of component leads and PCB contacts.
You wouldn’t try to paint a surface that wasn’t adequately prepared as the paint won’t adhere and will quickly lift and peel. The same applies to conformal coating, even when the contamination is from no-clean flux. Flux residues left on a PCB before coating can cause the coating to lift or delaminate, particularly when the pockets are isolated around solder joints rather than the overall surface. Complicating matters, coatings are generally semi-permeable, so they can “breathe,” allowing moisture to enter and soak into the flux residue and potentially lead to corrosion.
Board components also can carry various ionic/conductive contaminants to your assembly including cutting oils/fluids, biocides, and corrosion preventatives. Common nonionic materials—– process oils, mold releases, etc.—can also affect the assembly steps and cause damage down the line.
Flux factors
Many variables can affect the cleaning performance including the type of flux. R, RA and RMA fluxes, for example, are generally easier to remove with standard flux removers and isopropyl alcohol. No-clean fluxes are intended to stay on the PCB and are consequently more difficult to remove. Aqueous fluxes are generally designed to be removed in a batch or inline cleaning system with deionized water or water with a saponifier. Alcohol-based or specially formulated solvents can also be used to clean aqueous fluxes.
Higher solids flux, amount of flux, soldering temperatures—higher temperatures can bake on flux residues, making them more difficult to remove—lead-free soldering and the time between soldering and cleaning can all affect the cleaning process and its efficacy. These factors may necessitate more aggressive cleaning techniques or soak time.
ManualTechniques
Manual flux removal on the bench is common for low-volume electronic PCB assembly, rework, and repair. Because manual cleaning is more labor-intensive and less repeatable, results may vary from operator to operator. More automated cleaning methods are deployed for higher volume assembly and reduced variability.
A variety of flux removers and techniques are used for manual cleaning. Aerosol flux removers offer the advantage of a sealed system, which ensures fresh solvent every time and agitation by the spray pressure and pattern. A straw attachment allows spray with greater precision and a brush added to the nozzle enables simultaneous scrubbing. A trigger spray bottle is more common for water-based cleaners and isopropyl alcohol (IPA), but not for aggressive solvent cleaners. Liquid immersion, swab spot cleaning, and using pre-saturated wipes are also effective. The right technique depends on the type of contaminant or flux.
Automated Approaches
More aggressive cleaning approaches include ultrasonic cleaning that uses sound waves to create implosions within the flux residue, breaking it apart and lifting it off the PCB. Most equipment offers the option to heat the solvent to increase cleaning performance, of course only an option with a nonflammable flux remover.
Vapor degreasing is the go-to process for the most precise cleaning and most often used for aerospace and medical electronics. PCBs can be submerged in a sump of boiling solvent, in a rinse sump with ultrasonics, and rinsed in solvent vapors. Special solvents like azeotropes or near-azeotropes, must be used so the solvents will not change as they are boiled off and reconstituted in a continuous cycle.
Batch flux remover acts as a dishwasher for electronic circuit boards. PCBs are loaded onto a rack and water-based flux remover is sprayed over the assembly. The PCB stays in place as the machine goes through the wash, rinse and finally dry cycle. An inline washer functions more a carwash, where PCBs travel on a conveyor through wash, rinse and dry zones.
Education is the best strategy / Get Educated
Cleaning PCBs doesn’t have to be daunting, costly, or labor-intensive. But it does take planning along with the right tools and cleaning agents. It pays to be educated about your options and thoughtful about your processes. Fortunately, there are a wealth of resources that can help. This brief Chemtronics video provides simple when-to-clean tips and a BrushClean demo shows how a simple attachment can provide a thorough cleaning without cross-contamination.
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