Thin-film Parylene coatings protect many materials in medical applications because it conforms to all surfaces, edges, and crevices of a substrate for excellent protection from moisture and chemicals, and provides a dielectric barrier. But the coating requires precise processing characteristics.

Deposition equipment from Specialty Coating Systems, Indianapolis, Ind., (scscoatings.com) controls the coating rate and thickness. Parylene is vaporized and heated in a vacuum into a two-molecule gas. Then it's turned into a monomer and deposited as a transparent polymer film. Doing so requires an accurate, stable heat-up temperature, although the coating occurs in an ambient-temperature chamber. The deposition system must be kept precisely at 680 C (1,256 F), without variation. Heater and sensor manufacturer Watlow Inc., St. Louis, (watlow.com) developed a high-performance ceramic heater that reduced temperature deviation.

The ceramic-fiber heaters combine a high temperature iron-chrome-aluminum heating element wire with ceramic-fiber insulation that keeps high temperatures inside the chamber. Hence, energy heats the load, not surrounding equipment. The low-mass heaters, 10 to 15 lb/ft³ (160 to 240 kg/m³), quickly reaches process temperatures. Their high-insulation value and self-supported heating elements allow operating up to 1,204 C (2,200 F).

SCS applies the coating and sells the coating equipment. “With many systems running worldwide, machine uptime is important,” says Boyd. “We have had no recorded technical problems or maintenance issues with the heaters.”