Thin Film Metallization Coatings Shield Medical Devices from Harmful Interference
Oregon firm offers design and engineering assistance with proprietary vacuum metallization process
Plastic-Metals Technologies, Inc. (P-MT), headquartered in Tigard, Oregon, produces thin-film metallization coatings that are used as shielding to protect parts from electromagnetic interference (EMI), radio frequency interference (RFI), and electromagnetic compatibility issues (EMC). To create the thin-film metallization coatings, P-MT employs a form of physical vapor deposition (PVD) that uses a coating of copper with a second layer of aluminum, nickel, or stainless steel, depending on the standard environment for the medical device. The two layers are done under a high vacuum environment at a total thickness of 1 micron (0.00003937 inch).
According to P-MT Process Engineer Keith Schaefer, the quality of the coating is the main reason why customers choose P-MT. The coating has reportedly been shown in testing to provide better shielding effectiveness than leading paints, despite being only 1 micron (µ) thick. "Our process has been tested against the industry standard paints and provided a higher shielding effectiveness, which creates a safer product for our customer," Schaefer said in an e-mailed response.
Methods to test the performance of P-MT's coatings include point-to-point resistance (Ohms) testing to ensure that the coating is sufficiently robust to handle the requirements set forth by the customer's electrical engineers. "This has started to sway heavily toward four-point probe systems, which measure in sheet resistance (Ohms/□)," Schaefer said. "These sheet resistance measurements have become more of an industry standard for coatings used in EMI/RFI/ESD shielding solutions."
Testing for shielding effectiveness, important when trying to meet certain FCC restrictions for medical devices, typically includes radiated emissions, radiated susceptibility, resistance, and adhesion testing. P-MT tests customers' sample or prototype parts to ensure, through customer-independent testing, that the part meets all applicable requirements when P-MT's coating is used.
The adhesion testing of P-MT's thin-film metallization coating is "above and beyond what is necessary to make sure that P-MT customers are getting the best possible coating for their medical devices," Schaefer said. All parts are tested using the ASTM-D3359 standard for cross hatch tape testing, a standard used throughout the paint, plating, and powder coating industries. "The largest difference is that the coatings done by painters (~3 mils) are roughly 75 times larger than our thin-film metallization," said Schaefer.
Schaefer said that in addition to the quality of the coating, customers like its cost effectiveness because it's less expensive than paints and metallic enclosures. "P-MT is also chosen [by customers] for ease of use and implementation into a customer's project," he said. "There is no more having to design around paint thicknesses or massing amounts of paint in certain areas of the coated parts."
Plastic-Metals Technologies, an ISO 9001:2008 certified company, strives to make things easy for customers by providing assistance in design and engineering, as well as manufacturing services. "If a customer has a part that is still in the prototyping phase, P-MT will discuss the best possible layout for the coatings that the customer is looking to achieve," said Schaefer. Also, through the work of its engineering department and R&D testing, P-MT has created processes for customers looking for coatings that differ from its standard. "These tests may not always be fruitful, but they show how P-MT strives to meet any of the customer's goals through all of the combined engineering experience," he said.
A key strength of P-MT is its flexibility, reflected in its design of fixtures that are used to hold and mask parts safely inside the vacuum chamber. Noting that the thin-film metallization process is a batch process, Schaefer said that P-MT designs the fixtures so that they can be interchangeable across P-MT's different batch processing machines while maintaining the same results. This flexibility, he said, offers customers their own increased flexibility in size and production.
"Customers don't have to have large estimated annual usages to become a client, but instead only need to have the required fixturing to meet their lead time and manufacturing needs," he explained. "This allows us to get the high quality coatings P-MT is known for on all parts for all customers." He added that the amount of materials against which P-MT meets its own rigorous standards gives customers the flexibility to choose what material works best for their applications.
"The expertise that we have with materials is used across the board of our customers," Schaefer said. "P-MT has been evaporating metals onto plastics for the past 12 years and has also begun, with exceptional results, depositing on composite materials and resins."
Applications for P-MT's thin-film metallization coatings have included 3D printing options, such as Selective Laser Sintering (SLS), stereolithography (SLA), and Fused Deposition Modeling (FDM). The company can provide an EMI/RFI/ESD coating on prototype parts to give customers the testing flexibilities that are necessary to meet FCC classifications and CE marking, Schaefer said. In addition, P-MT has provided some decorative and reflective coatings for its customers, depending on their needs and what they are trying to achieve. The company has also helped customers meet specific needs with respect to subassemblies by providing form-in-place gasketing, light piping, heat staking, ultrasonic welding, application of decals, and inserting.
In addition to being ISO 9001:2008 certified, P-MT (www.p-mtinc.com) holds UL certification and is compliant to ITAR and RoHS.
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