EMC and electronic enclosure design: Page 4 of 4

May 16, 2019 //By Kemtron
EMC and electronic enclosure design
RFIEMI screening is a discipline that is of interest to both the electronic engineer and the enclosure design engineer. The electronic engineer must take EMC into account when designing PC boards by careful component and circuit layout, using PCB shielding cans as small Faraday cages over problem components, paying attention to wiring runs, use of filters and ferrites etc.

Gaskets in grooves

For the typical electronic enclosure, groove mounted gaskets such as “O” rings are generally a better option than surface mounted gaskets as when the gasket is compressed in the groove the two mating flanges can come into contact with each other thereby enhancing the screening performance by improving low contact resistance, “O” rings in grooves are also a much more cost effective solution and the groove also acts as a compression stop, thus protecting the gasket.

Most types of gaskets can be fitted into grooves, however a solid conductive elastomer gasket when compression forces are applied cannot change volume and has to deflect, and therefore the groove needs to be the same volume or more as the gasket to let the gasket material fill the space provided for it. If the gasket overfills the groove, damage and gasket failure can occur when the mating flanges are closed together.

 

Corrosion

An EMC gasket that is placed between two conductive surfaces is generally of a different material to the mating surfaces. In certain conditions this can lead to severe problems of bimetallic galvanic corrosion and degradation in shielding effectiveness. There are two ways of reducing the corrosion risk. One is to use a separate non-conductive environmental seal outboard of the EMC seal therefore isolating the joint from the environment. This would allow the use of materials that would otherwise be unsuitably matched. However limitations on flange widths and the increased cost of using two gaskets can make this impractical.

A far better method is to try and match as near as possible the material of the gasket and the flanges thus reducing the electro potential difference between them. Kemtron offer a complete service offering a complete range of EMC gaskets and components for enclosures and PCB’s
 
www.kemtron.co.uk

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