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78 SMT Magazine • March 2017 the factory floor. Vapor degreasing systems, in contrast, work vertically, and require little space and less energy than aqueous systems. The small, delicate parts used in PCBs can be a challenge to clean in an aqueous system. Due to the chemical characteristics of a water molecule, water often cannot get into the tightest spaces or smallest apertures. This means those hard-to- reach locations are not wetted and—as cleaning experts all understand—if you cannot wet, you cannot clean. Chart 1 compares the wetting abil - ities of water to a variety of popular solvents. Big aqueous cleaning systems also have a much slower through-put than a vapor degreas- er. I have personally seen 15-meter long aqueous systems using 45-minute cycle times, while a va- por degreaser typically cleans a basket of PCBs in 8–10 minutes. Energy is a big issue today. Aqueous systems require high temperatures to be effective, more energy to dry the parts after cleaning, and still more energy to treat the water after use. Soggy aqueous systems also inject humidity into the at - mosphere of the workspace, requiring more elec- tricity to cool and dehumidify, but it requires an enormous amount of energy to heat water. As noted above, aqueous cleaners generally will con- sume at least six times more energy than a vapor degreaser cleaning the same quantity of parts. Filtration is also problematic with water- based cleaning systems because water does not easily traverse 2 or 3 micron filters. The only way to deliver micron-grade filtration is with big, en- ergy-hungry pumps to force the water through the filter. Also, the rinsing and drying process is much more complex. Blowers or heated dryers often are used to reach nooks and crannies, and even then, spotting or corrosion can be a problem. These blowers and heated dryers also require additional energy to operate. Finally, bioburden, which forms when as - sembled devices come in contact with residual organic materials, can be a problem with aque- ous systems, but not with solvent-based systems. For a medical device manufacturer that has had to re-clean, re-package or scrap devices that have been affected by bioburden, the vapor degreaser system can offer significant savings in time and money. To sum it all up, not only does solvent clean- ing offer an environmental benefit, it is also a cost savings for almost every manufacturer. Innovative Solvents and the Environment Today's modern solvents meet strict envi- ronmental standards. They are all complete- ly ozone-safe, for example. They meet Registra- tion, Evaluation, Authorization and Restriction of Chemicals (REACH) requirements, are TSCA registered and some of the newest choices have virtually no global warming impact. These in- novative new solvents available on the market are not only gentle on the planet, but also deliv- er consistent and reliable cleaning with the low- est overall costs. Cleaning trials should be a prerequisite be- fore making choosing a cleaning method. Tests usually involve collecting a standardized sam- ple of contaminated parts and sending them to the chemical company's lab. Any quality ven- dor should be willing and able to perform a modest amount of testing. The vendor should provide a detailed written report and often will perform these services free of charge. The continued miniaturization of compo- nents is making critical cleaning of PCBs a chal- lenge. In general, the need get the job done right, while protecting people and the envi- ronment, and the incessant pressure to reduce costs combine to make solvent cleaning a very attractive option. The companies who choose the most versatile, flexible, low-risk option that meets all the critical cleaning requirements are the winners, and the way to come out on top is through selecting solvent cleaning using a va- por degreasing process. SMT Michael Jones is the vice president of MicroCare Corp. Sally Stone is a technical specialist at Hart Marketing. MINIATURE COMPONENTS ON PCBS REQUIRES FLEXIBLE CLEANING METHODS