Reliable, Consistent Temperature is Critical to Parylene Coatings for Medical Products

Uniform and repeatable temperature is a critical process variable for many manufactured products. The slightest variation can result in lost product, wasted time and headaches for both the manufacturer and supplier. Such is the case for Specialty Coating Systems (SCS), a provider of Parylene conformal coatings for a variety of industries.

Parylene coatings offer protection for a variety of surface materials used in medical applications, including stents, electrostimulation devices, electrosurgical tools, catheters, elastomeric products, forming devices, and medical electronics. Parylene thin-film coatings conform to all surfaces, edges and crevices of a substrate and provide excellent moisture, chemical and dielectric barrier protection. Since Parylene is not a liquid, the coating does not suffer the meniscus and edge effects of conventional liquid coatings. SCS has been developing and applying Parylene coatings to critical medical devices for more than 35 years.

"Parylene is chemically and biologically inert, so the human body will not reject or react negatively to products that are coated in Parylene," explains Bill Boyd, equipment program manager at SCS. "This protects the body from the device and the device from the body."

SCS's Parylene deposition systems are designed for accurate and repeatable operation. Operating temperatures and pressures are continuously monitored and recorded, and can be uploaded for system and coating run analysis.

The deposition system must be kept precisely at the high temperature of 1,256°F, with no variation. With a requirement for precision operating temperature, SCS turned to Watlow to develop a high performance ceramic heater that would reduce temperature deviation.

Watlow's ceramic fiber heaters integrate a high temperature iron-chromealuminum (ICA) heating element wire with ceramic fiber insulation. The ceramic fiber insulation isolates the high temperatures inside the heated chamber from the outside, so energy is used to heat the load instead of the surrounding equipment. Ceramic fiber heaters are low mass. The heater's high insulation value and selfsupported heating elements enable operating temperatures up to 2,200°F.

SCS Parylene coatings are applied to a variety of surfaces with deposition equipment that enables control of both coating rate and thickness. Polymer deposition takes place at the molecular level as Parylene dimer, a white powder, is vaporized under vacuum and heated to form a dimeric gas, then pyrolized to cleave the dimer to its monomeric form, and finally deposited as a transparent polymer film. This manufacturing process takes gas to a solid and essentially skips the liquid step, and that requires a highly accurate, stable heat-up temperature. Coating occurs in an ambient temperature chamber and components are required to have only a reasonable vacuum tolerance.

SCS not only has nine coatings centers around the world, they also sell the equipment to customers. With many systems running worldwide, up-time of the machines for SCS is important. With Watlow's reputation of quality heaters, SCS does not have to worry about heater failure in their equipment.

"We have had no recorded technical problems or maintenance issues with Watlow heaters – and that reliability and peace of mind is important for our tight process parameters," Boyd says.