By Ultrasonic Systems, Inc. (USI)
USI’s core technology is called tCAT, a proprietary nozzle-less ultra-Thin Coating Application Technology for the thin, uniform application of a wide variety of coatings from pure solutions to high-solids suspensions and slurries. tCAT utilizes “nozzle-less” ultrasonic spray technology combined with a precision metering pump liquid delivery system, which are part of a coating system platform with a motion and positioning system for the spray head, and a transport system for the substrates to be coated. How it Works: The Ultra-Spray head is an integrated assembly consisting of an ultrasonic transducer with a spray forming tip, a liquid applicator and air directors. The ultrasonic transducer vibrates at an ultrasonic frequency (> 20 kHz). The particular ultrasonic frequency is selected based upon the material to be sprayed and the coating application requirements. In general, a lower frequency ultrasonic transducer is capable of spraying a higher viscosity liquid and producing higher flow rates. The amplitude of vibration of the spray-forming tip is also set with the ultrasonic generator. The coating liquid is delivered to the spray-forming tip on the ultrasonic transducer by liquid applicator. The liquid is stored in a reservoir and fed to the liquid applicator at a precisely controlled flow rate by a positive displacement Precision Metering Pump (PMP). The ultrasonic vibrations of the spray-forming tip break up the liquid into small drops and propel them from the tip in the form of a spray. The spray produced with ultrasonic energy alone has a very low velocity “sheet-like” pattern. Air directors are used to produce air streams to shape and accelerate the ultrasonically-produced spray. The air director impinges a jet of air on tip of the spray head opposite the liquid feed side. The resulting airflow entrains and expands the ultrasonically-produced spray to produce a flat (rectilinear) pattern up to five (5) times the width of the pattern produced by the ultrasonic energy alone. When using the air directors, the spray pattern width is a function of the spray-forming tip width and tip-to-substrate distance. Coating Thickness Uniformity: In general, the uniformity and thickness of the applied coating layer are directly related to the following factors: - Uniformity and stability of the spray pattern produced by the ultrasonic spray head - Accuracy and stability of the coating flow rate delivered to the ultrasonic spray head - Consistency of the speed of the ultrasonic spray head relative to the substrate - Programmed coating recipe – number of applied layers, the application path, and the coating flow rate The speed and motion path of the ultrasonic spray head is controlled with a closed-loop servo drive system. The servo drive is tuned for uniform head speed so the variation of the head speed is negligible. The liquid flow rate is determined by the rate of displacement of a piston in the pump. The motion of the piston is controlled by a micro-stepping drive system so the variation of liquid flow rate is also negligible. For a given coating recipe, the variation in the total amount of liquid applied to the substrate is less than ±0.1%. This can easily be verified since the system software logs the total amount of liquid applied to each substrate that is coated. Any variations in the head speed and the liquid flow rate are accounted for in the process log. Examples of the coating uniformity achieved with tCAT are shown below. Example #1 – Photoresist on Touch Panel Glass: In this example, a 10% solids formulation of photoresist is applied to the touch panel glass plate at a wet film thickness of 15 microns. The glass plate is dried on a hotplate and the resulting dry thickness is approximately 1.5 microns. As shown in the measured thickness plot, the thickness variation is negligible. Example #2 – Fuel Cell Coating: In this example, a precious metal-based catalyst is formulated at 5% solids by weight. The required loading is 1.5 mg per square centimeter. The loading achieved with tCAT is 1.45 to 1.55 mg per square centimeter, 99% of the time. Example #3 – EMI Shield Coating to Components: In this example, a high-density silver slurry with a solids content of about 72% is applied to components. The cured coating layer provides EMI shielding to the components when they are placed into circuit assemblies. The top side layer thickness is 6 +/- 0.5 microns and the side surface thickness is 3 +/- 0.5 microns. The repeatability of this process at different process settings is shown in the thickness variation plot. Data provided by Henkel Electronic Materials. Example #4 – Anti-reflection Coating to Solar Glass: In this example, an anti-reflection coating is applied to a 1,200 mm x 600 mm glass plate. To provide the required anti-reflection properties a uniform coating layer thickness of 120 nanometers is required. The thickness of the dry layer was measured at 80 points across the surface of the glass. The measured data is: Target: 120 nm; Ave.: 120.2; Min.: 117.5; Max.: 122.9; S.D.: 2.1. Liquids Applied with Ultra-Spray Technology: A wide variety of coating liquids can be applied with Ultra-Spray ultrasonic spray head technology from solutions and mixtures to high solids slurries and suspensions. A partial listing of these liquids include: Solutions & Mixtures - solvents - aqueous based coatings - polymers - urethanes - acrylics - photoresists - polyimides - anti-reflective coatings - anti-smudge coatings - anti-scratch coatings - optical coatings - etc. Slurries & Suspensions - precious metal / carbon based catalysts - ceramic based catalysts - conductive inks - nano particle coatings - EMI shield coatings (high solids) - etc. Medical & Biomedical Coatings - drug eluting coatings - bioresorbable polymers - anti-restenosis coatings - reagents - protective coatings - diagnostic agents - theraputic agents - disinfectant agents - etc.
