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Improving Adhesion of Coatings to PCBs Using Plasma Treatment
Continued from previous page
equipment to run parts and conduct experiments, with full customer in- volvement. For this particular project, QSi
dispatched two of its senior chemists, Eric Washington and Dr. Lewis, to work onsite at PVA TePla’s lab with Dr. Barden. The task began by secur- ing hundreds of samples of the com- ponents on the PCB from the cus- tomer and its suppliers so that tests could be conducted. The silicone over-molding was
then applied over a variety of cata- lysts and primers and tests per- formed to determine the degree of de- lamination. In addition to conducting sur-
face tests with a contact angle go- niometer, Dr. Lewis also devised cri- teria to compare the options. As part of the process, the sili-
cone formulations were altered in an attempt to obtain better interaction or adhesion to the plasma coating. The plasma coatings were also varied in type, thickness, and composition. Dr. Lewis estimates that the
total number of permutations evalu- ated, considering silicone formula- tions, plasma coating variations, and quantity of components, resulted in over 4,500 samples being evaluated over an eight-month period. This led to the development of a multistep modification process to the PCB sur- face, completed in a batch process in a plasma chamber designed and manufactured by PVA TePla.
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a precision cleaning and surface acti- vation treatment followed by the dep- osition of an inert chemical primer that serves as a tie layer for the over- molding and provides a uniform sur- face energy for the silicone to bond. Each batch can process 15 to 20
boards in approximately 20 minutes before the proprietary silicone for- mulation is applied. Although the process was performed in a batch chamber system, it can also be imple- mented on an in-line chamber sys- tem to meet high-speed, large-vol- ume production requirements. Even with the process now firm-
ly established for the existing cus- tomer, Dr. Lewis still continues to make frequent visits to PVA TePla to develop new methods of improving the adhesion between QSi’s different silicone chemistries and various sub- strates.
“There are always applications
where a customer needs improved adhesion,” says Dr. Lewis. “Building of adhesion is a function of time and temperature, but most customers are not patient with the time and prefer to run processes at lower tempera- tures. We are always searching for ways to drive improvements in adhe- sion toward shorter times and ambi- ent conditions.” Contact: PVA TePla America,
Inc., 251 Corporate Terrace, Corona, CA 92879 % 951-371-2500 fax: 951-371-9792 Web:
www.pvateplaamerica.com r
August, 2016
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