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Page 62


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May, 2021 Replacing nPB in PCB Cleaning Processes By Emily Peck, Senior Chemist, MicroCare, LLC


processes since the 1990s. It is used as an alternative to CFC-113, methyl chloroform, hydrochlorofluorocarbons (HCFCs) and per- fluorocarbons (PFCs) in many critical PCB cleaning and drying operations where relia- bility is paramount. Relatively inexpensive and a good cleaner,


A


nPB is coming under scrutiny by the U.S. EPA, OSHA and American Conference of Govern - mental Industrial Hygienists (ACGIH). Based on toxicological research performed by ACGIH, the permissible exposure limit was reduced from 10 ppm to 0.1 ppm in 2014. In 2018, the EPA added nPB to its Toxic


Substance Control Act (TSCA) list. In August of 2020, the EPA reported that nPB presents unreasonable risk to human health and should be restricted as a PCB cleaner. This report is only a preliminary step for the EPA. Many experts anticipate that it will lead to a complete ban on nPB by the end of 2022. As of July 2020, nPB was banned in Europe with many other countries likely to follow. Fortunately, there are a number of good


nPB replacements that are less hazardous for workers, better for the environment and clean just as well, if not better, than nPB inside a modern vapor degreaser. Many of the nPB replacement cleaning


fluids provide consistent PCB cleaning quali- ty, cost savings and greater throughput. Plus, they have more favorable toxicity pro- files, making them safer for both people and


n effective and reliable cleaner, n- propyl bromide (nPB) has been widely used in industrial PCB cleaning


the planet. Most nPB replacement cleaning fluids are lab-tested and analyzed to ensure the cleaning results are reliable, consistent and just as good as nPB. Cleaning efficiencies are often maintained or improved, even on hard-to-remove lead-free and no-clean flux residue. Modern cleaning fluids are excellent at removing a variety of soils on PCBs left behind from the production process. These include


mentally sustainable cleaning fluid. Most vapor degreasing systems comprise a top-load- ing batch-style cleaning machine with two com- partments: the “boil sump” and “rinse sump.” In the boil sump, PCBs are immersed in


heated fluid and then transferred to the rinse sump. Ultrasonics may be used to dislodge stubborn soils. The PCBs are rinsed in pure uncontaminated fluid or within fluid vapors. The PCBs emerge from the vapor degreaser clean, dry, cool enough to handle easily, and immediately ready for the next step in the process.


High Solvency, Low Viscosity Many modern nPB replacements have a


high solvency to dissolve contaminants, yet are formulated to not damage delicate elec- tronic components or substrates. The strength of a PCB cleaner is measured by its Kb value, which is a continuum of cleaning strengths from very mild to extremely aggressive. A mild, plastic-safe cleaner made of alco-


A fluid supplier with lab testing can verify that a cleaning fluid is the best fit for a customer.


fluxes, pastes, marking inks, fingerprints, and adhesives.


Vapor Degreasing Vapor degreasing is a closed-loop system


that requires two components: a closed-top vapor degreaser and nonflammable environ-


hol might have a Kb value of 10 or so. nPB has an Kb value of 130. This means nPB is so strong that it can attack plastics, elastomers and adhesives. In contrast, most modern nPB replacements have a Kb value of about 100 which makes them safe to use on a variety of electronic components, especially those made with mixed materials. Most of the modern nPB replacements


also have low viscosity. This is especially help- ful with PCBs that are small, multilayered and


Continued on page 68 CableEye® HVX Systems


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