Interior of GTEM cell and probe for electromagnetic compatibility testing

Interior of GTEM cell and probe for electromagnetic compatibility testing

EMI gaskets can be a big advantage when trying to protect an enclosure from both environmental and electrical ingress. However, the design of EMI gaskets can be a difficult challenge for electrical and mechanical engineers alike. Making an incorrect decision leads to expensive parts that are at risk of failure.

There are four major topics to consider when searching for a solution:

  1. Design of the assembly
  2. Environmental sealing
  3. EMI shielding
  4. Estimated annual production quantities

Along with the material selection, the design of the assembly is one of the biggest factors of the enclosure’s ability to seal. The inherent size, stiffness, flatness and compression mechanisms of the enclosure play a major role in the material options. For example, a sheet metal cabinet with latches may require soft and thick combination gaskets due to the materials forgiving nature, while a machined alloy enclosure with bolts can enjoy the robust sealing of a hard solid rubber-like SNE-540.

Clearly defining what the gasket needs to keep out is another vital input when considering solutions. Using the IP or NEMA scale is a good way to communicate whether you’re trying to keep out dust, rain or 10′ of water. Different classes of materials have inherent strengths. For example, while Condux Plus makes a great dust gasket touchscreen, it wouldn’t help with water ingress.

Declaring the concerning frequency range, and how many decibels of energy must be attenuated, is often the most difficult metric to quantify because the answer may require testing of a prototype to be certain. MIL-DTL-83528 is a handy test specification that is used by the military to define standard performance levels. But use caution when referencing this spec, because the materials called out are narrowly defined and will unnecessarily limit the available options. This spec also falls short of the higher frequency levels expected from 5G EMI shielding requirements.

Another commonly overlooked point is how many parts will be needed for production (not prototypes). A high volume application might benefit from a custom molded gasket, which uses a soft shape but requires expensive tooling up front. A low volume application may not be able to sustain this high tooling cost, and solutions should be limited to cutting a part from a sheet, or basic fabricated part.

There are many other important topics like compression stops, galvanic corrosion risk, and ideal compression levels for an EMI gasket. If interested in learning more, contact a Stockwell Elastomerics Application Engineer for custom guidance tailored to your unique design.

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