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Cleaning PCBs - Understanding Todays Needs
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Authored By:P.J.Duchi, Anne Marie Laugt, Marie Verdier, G.Abidh Inventec Performance Chemicals Bry sur Marne, France TranscriptBecause of the phase out of CFC's and HCFC's, standard solder pastes and fluxes evolved from RA and RMA fluxes, to No-Clean, to low residue No-Clean, to very low residue No-Clean. Many companies came out with their cleaning solutions, aqueous and semi-aqueous, with each product release being more innovative than the previous one. Unfortunately for most of the suppliers of cleaners, two other trends appeared; lead-free soldering and the progressive miniaturization of electronic devices. In addition, assembly processes have been modified due to smaller components and more compact board assemblies. This cleaning study shows that there are many cleaning parameters affecting its efficiency. Cleaning performance is based on the mastering many parameters. When the choice is based on solvency power, the lowest surface tension and the most efficient process, a perfect job can be reached matching the toughest specifications. SummaryBecause of the phase out of CFC's and HCFC's, standard solder pastes and fluxes evolved from RA and RMA fluxes, to No-Clean, to low residue No-Clean, to very low residue No-Clean. Many companies came out with their cleaning solutions, aqueous and semi-aqueous, with each product release being more innovative than the previous one. Unfortunately for most of the suppliers of cleaners, two other trends appeared; lead-free soldering and the progressive miniaturization of electronic devices. Past chemicals like CFC's, HCFC's, brominated solvents, detergents and glycols can not do a good cleaning job anymore because most flux formulations have changed. Also, assembly processes have been modified due to smaller components and more compact board assemblies . Thus , it is important to remember that the world is composed of two main things: organics and inorganics. Organics are made of resins and activators, whereas i n organics are made of salts, metallic salts and fillers. Cleaning performance is affected by three main criteria. The first involves the Hansen Parameters which is a characterization of a contaminant to be dissolved and which can be simplified by the solvency power of a product also known as the Kauri Butanol Index(KB Index). The second is surface tension, expressed in mN/m.T his parameter must be considered because when the cleaning product cannot make contact with the contaminants under or around components ,the contaminants cannot be dissolved. This second parameter drives us to the third point, which is physical parameters like temperature, mechanical activities, and the duration of the process. The mastery to manage all of these parameters while facing high-tech miniaturization and environmental care, like ROHS, REACH, etc. brings innovation to cleaning in this electronic world ConclusionsThis cleaning study shows that there are many cleaning parameters affecting its efficiency. The final aspects and performances of these PCBs are based on the mastering of cleaners, size of the assemblies, agitations and the cleaning processes. When the choice is based on solvency power, the lowest surface tension and the most efficient process, rather than ideas and opinions, then a perfect job can be reached matching the toughest specifications. The co-solvent / Vapour degreaser process with formulated hydrocarbon and HFE (hydrofluoroether), combined with ultrasonics or jets show the best performance. Contamination is below 0,2 ug of Eq NaCl/cm2 for ranking 9 and with a perfect visual aspect under components. No damage of quartz could be notified during trials. Initially Published in the IPC Proceedings |
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