EMI and RFI Shielding

EMI and RFI shielding includes coatings, gaskets, enclosures, sealants, resins and other products or materials that block out electromagnetic interference (EMI) and radio frequency (RF) interference. EMI is high-frequency interference caused by electronic components, fluorescent lamps, and industrial equipment. RFI is similar to EMI, but affects lower frequencies within the electromagnetic spectrum. In the United States, the Federal Communications Commission (FCC) establishes limits for EMI and RFI in order to prevent interference with communications devices and systems. Typically, EMI and RFI shielding is used in medical equipment, military hardware, telecommunications systems, and anti-static applications. Resins or compounds with a high degree of electrical conductivity (low resistivity) are used in thick-film metallization and electrical interconnections. Dielectric compounds are used to form a barrier or isolator between electrical or electronic components.

EMI and RFI shielding is made from rubber, metal, plastic, textile, and composite materials. There are many different types of products. Examples include adhesives, coatings, paints, gaskets, magnetic shielding, and specialty materials. Casting resins are plastic or elastomeric compounds that consist of two-part (A+B) systems in which A is the resin and B is the catalyst or hardener. Encapsulants are used to seal or cover an element or circuit in layers that are usually not more than 100 mils thick. Molding compounds that contain EMI and RFI shielding are suitable for processes such as injection molding, compression molding, blow molding or film extrusion, reaction injection molding (RIM), and resin transfer molding (RTM). Gap filling or underfill compounds are available as flexible sheet materials, liquid sealants, and form-in-place (FIP) compounds. Mastics such as tape and film are used to fill in gaps or surface irregularities. Thermally conductive resins that provide EMI and RFI shielding are also available. 

Specifications for EMI and RFI shielding include electrostatic discharge (ESD) protection, rated immunity, and electrical fast transients (EFT). Electrostatic discharge (ESD) is a sudden and momentary flow of current that occurs when a stored electric charge finds a path to an object at a different electrical potential. Rated immunity for EMI and RFI shielding is defined according to standards from the International Electrotechnical Commission (IEC). On-chip ESD, EFT and EMI protection structures ensure compliance with the requirements of IEC1000-4-2, IEC1000-4-3 and IEC1000-4-4.

• Designing For Manufacturing: Don't Forget the access hardware
  Latches, hinges, and other access hardware are important parts of a design. But keep the manufacturing process in mind when specifying them. Supervisor, Customer Application and Development Center...
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• Designing inside the box
  Self-clinching fasteners lose the loose hardware. Broaching fasteners install permanently in all types of printed-circuit boards, as well as in components made from acrylics or polycarbonates. Clinch...
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• EMI Shielding With Perforated Metals
  One of the most common uses for perforated metal is to enclose electrical devices to attenuate the EMI/RFI radiation they emit and to ventilate them at the same time. Many questions have been asked...
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Part Numbers for EMI and RFI Shielding