Assembly - February 2009 - (Page 41) parameters vary depending on the material, part size and bonding objectives, says Jeff Gradus, regional sales manager for Tantec EST Inc. (Glendale Heights, IL). No special part designs are required—complex shapes and continuous films can be treated. Plasma can be directed at areas as large as a dashboard or as small as the inside of a needle hub on a syringe. “Plasma is isotropic and nondirectional,” says Demetri Chrysostomou, Ph.D., director of technology at PVA Tepla America Inc. (Corona, CA). “It conforms to any three-dimensional object. It gets into nooks and crannies. It can get under silicon wafers on chip carriers and into fine polymer capillaries. It doesn’t suffer from lineof-sight problems, and it doesn’t cast a shadow.” Despite the energy applied to the gas, plasma treatment is a relatively low-temperature process. It is environmentally friendly, and it’s safe for operators. A small amount of nitric oxide is emitted during treatment, and this may need to be vented depending on the layout of the system. The treatment does not produce ozone. Plasma treatment does not change how the plastic looks or feels, nor does it alter the material’s inherent properties. In fact, it’s impossible to distinguish between treated and untreated parts except by checking how well liquids wet their surfaces. “Because the treatment only penetrates the substrate to a depth of about three molecules, the physical properties of the substrate are not affected,” says Smith. Plasma treatment is not limited solely to plastics or adhesive bonding applications. Plasma improves the bondability of metals, glass and ceramics. It enhances wettability and adhesion for inks and paints. It facilitates joining of dissimilar plastics in overmolding or in-mold assembly applications. And, it sterilizes plastic parts for medical applications. Batch vs. Continuous Process Plasma treatment can be done as Plastic tubing for a medical application tumbles inside a rotating plasma chamber. Photo courtesy PVA Tepla America Inc. When plasma treatment is done as a batch process in a vacuum chamber, engineers can control every process variable, including the composition, flow rate, pressure and concentration of the gas, and the frequency and wattage of the electrical energy. Photo courtesy Tantec EST Inc. www.assemblymag.com February 2009 / ASSE M B LY 41 http://www.assemblymag.com
For optimal viewing of this digital publication, please enable JavaScript and then refresh the page. If you would like to try to load the digital publication without using Flash Player detection, please click here.