| EMI/RFI shielding Frequently Asked Questions |
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EMI / RFI stand for ElectroMagnetic Interference and Radio Frequency Interference (RFI is just EMI over the range of 1kHz - 10GHz). Electromagnetic radiation and radio frequency radiation are all around you! Their effects on the human body are the subject of fierce debate, but their effect on electronic devices is clear. They interfere. Sensitive components and circuits can be disrupted by interference from sources like power supplies, fluorescent lights, electric motors, switches and relays, even IC's. The clock in your computer oscillates and produces interference. In short, almost all electronic circuits develop some level of EMI and / or RFI.
Shielding from EMI / RFI is done for two primary reasons: (1) to keep your electronic device from interfering with others, or (2) to keep other devices from interfering with yours. Often, regulatory agencies such as the U.S. Federal Communications Commission or the EU dictate standards for both emissivity of EMI / RFI and sensitivity to interference. |
Why use EMI / RFI shielding coatings? The ideal enclosure for electromagnetic shielding would be a seamless sphere manufactured from highly conductive material, such as copper, aluminum, silver, or gold. Unfortunately, this solution is impractical and would render other functions of the enclosure useless. In the real world (the world of plastics), any enclosure designed in metal may be impractical and cost prohibitive. Often the cost constraints or even the shape required of an enclosure dictates use of plastic injection molded parts. Most plastic, however, is virtually transparent to EMI / RFI. For this reason, coatings have been developed to add shielding characteristics to plastic enclosures. These conductive coatings reflect the interfering radiation. Some common shielding coating materials are silver, copper, nickel and graphite. |
What are the properties of the different types of shielding coatings? (All data herein represent typical values for various types of coatings. For specific ratings and details, contact the manufacturer of a specific coating.) |
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What are dB's and ohms/square/mil? Since shielding coatings primarily reflect the offending radiation, you would think that it would be expressed as a percentage of radiation reflected, right? No, the measure of shielding effectiveness is expressed in decibels (dB), where: |
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There are many manufacturers of shielding coatings. We are not affiliated with any manufacturer and list them as a courtesy. Acheson Colloids : 1-800-255-1908 www.achesoncolloids.com Parker Chomerics : 781 935 4850 www.chomerics.com Spraylat. : 914-699-3030 www.spraylat.com W.C. Richards : 708-385-6633 This is not intended to be a comprehensive list of manufacturers. |
Why should I outsource this process? Obviously, we're biased. We want your business, and there are very good reasons to give it to us! To start, outsourcing EMI / RFI shielding coating as a process allows a manufacturer or injection molder to stand out from its competitors. As described above, these coatings provide protection from serious problems that affect delicate electronic components. They enhance the usefulness of your enclosures, and with the right choice of coatings, protect from emitting harmful radiation. Until recently, these coatings were used almost exclusively on military, aerospace and high-tech commercial products. More and more, though, commercial products are turning to these coatings for the benefits listed above. Given that, the choice is to outsource or perform the process in-house. Without further ado, the pros and cons of outsourcing: Pros: 1. No capital investment and no equipment obsolescence. All of the expense for equipment to process a specific coating job is placed on the vendor (us, nudge nudge). Starting or upgrading any coating process may involve spending thousands upon thousands of dollars. 2. No perpetual environmental liability. By outsourcing, all hazardous waste management, OSHA regulations and VOC problems are never yours to begin with. This can be a significant benefit to outsourcing, since many coatings are laden with VOC's and the associated safety factors that come into play are varied. In one case here in Florida, a company had to shut down for a day due to the use of a coating for touch up inside the facility. Over 100 people were sent home complaining about fumes when the odor spread through the manufacturing floor. 3. Expansion of an assembler's sale base. An injection molder or enclosure provider that does not presently have coating capability can now bid on work including the shielding coating instead of forcing the OEM to fend for itself. Knowing that OEM's can utilize this service, allowing them to use any injection molder or enclosure supplier they want, it makes sense to offer them the whole package. 4. Overhead reduction. Direct labor can be reduced or redirected (a big bonus in today's labor market). When considering this reduction, do not neglect the cost of continuous on-site process engineering and maintenance on any process setup in-house. 5. Immediate access to technology and expertise. This allows you to hit the ground running. Setup of the machines, application techniques and troubleshooting are handled by the experts (us again, nudge nudge). Cons: There may be a few disadvantage to outsourcing this work, but we at Thermospray have worked hard to eliminate these concerns. Process technology is one concern, but as previously mentioned, because we specialize in coatings, we try to stay abreast of the current technology. Pricing is obviously a huge concern. We at Thermospray have the expertise to minimize the cost of coating your parts. We buy many coatings in bulk and can pass the savings on to our customers. We also deal with hundreds of types of enclosures, in volumes of hundreds per day, so we have the techniques to deal with your product in the most efficient way possible. We will gladly coat your samples to demonstrate our quality while allowing us to fine-tune the process and give you the best possible price. |