In response to an EMC CISPR 11 EMI/RFI shielding requirement, specifically radiated emission (RE) and radiated susceptibility (RS) requirements, a medical equipment company requested a design solution which included the application of a transparent conductive coating (<50 ohms/sq. ITO coating) to their polycarbonate filter. Dontech worked with the customer to identify an option which met the EMC requirements, but also during the design learned about an additional extensive wash-down compliance and wash-out issue. This wash-out issue was the result of the filter being used in high ambient light that often occurs in the operating room. This customer was also concerned about product losses, because over 20% of these optics were being damaged during assembly with the incumbent supplier’s solution.
Dontech redesigned and manufactured the entire optical filter assembly in house. This design included the use of a high-performance antiglare hard coating on the front side of the filter, which addressed readability and met the outer surface wash-down and sterilization requirements. The design utilized an enhanced ITO coating on the rear side to improve readability and achieve the necessary EMI/RFI shielding requirements. Cost control considerations were also incorporated into the redesign. Since we produced the entire filter, many of the coatings could be applied in large sheets rather than individually batch processing parts. This not only helped keep processing costs down, but it also lowered the handling steps of individual parts, which always lowers the risk of potential product damage.
To complete the sealing of the front enclosure, Dontech applied a secondary hard coating and a die-cut VHB tape to the machined step of the filter, extending the life of the filters by protecting the edges from wash-down fluids. This solution provided protection to this unprotected surface and sealed the filter into the bezel. A black border was also applied to the optical filter to mask the non-active perimeter of the LCD. The EMI/RFI portion of the filter was terminated with a perimeter fabric over foam EMI/RFI shielding gasket. All parts were 100% pressure tested to ensure they would meet both the chemical wash-down and push out requirements.
To further help solve the damage that was occurring in the next higher assembly, Dontech cleanroom-trained technicians were able to package the bezel filter assemblies. The filters could be quickly and easily installed without the extra handling associated with cleaning in the next higher assembly, providing significant value to the customer in yield improvement
Dontech is an AS9100D and ISO-9001:2015 certified designer and manufacturer of optical filters, laminations, and thin film coatings for the precision optics, display, and touchscreen markets.
Since 1971, we have designed and manufactured custom components that enhance the performance of optical systems from concept to final system delivery.
