Electronics Protection - Summer 2017 - 10

Feature
Holland continued from page 9

18. Pin Mounting - There are also systems with pins (Fig. 7) for though
holes or covers with integrated pins that can be soldered directly
onto the PCB.
19. Shield Layout - Cooling holes can be made in the cover or steps
to prevent short circuits (Fig. 8) with the tracks on the PCB. Covers can
also consist of a fixed part on the PCB (fence) and a separate cover
(Fig. 9) which is clipped on to this fence.

Figure 7. Pin mounting used to mount PCB shielding cans

Covering the Entire PCB

20. Another option is covering the entire PCB in shielding material. This can be
achieved either by means of a small housing, custom-made to exactly the right
shape, or by simply wrapping or sticking material around the PCB. Foils, textiles,
stretch material, and wrapshields cut to the appropriate shape, are easy to apply.
Since it is always important to prevent short circuits, all materials can be provided
with insulation layers.

Figure 8. (left) Example of a shield
layout with holes and openings for
cables. Figure 9. (right) Fixed part on
the PCB and a seperate cover

Cable Shielding

21. Cables Inside the Housing - Once the PCB is covered, the attached cables can also be shielded. The longer a cable,
the higher its potential for emitting lower frequencies. Shielding a wire inside the enclosure will also prevent crosstalk and will make the main enclosure act as a cavity, and thus amplify the radiation. To prevent this, the enclosure
can be (partly) laminated with EM absorption material.
22. For round and flat cables we produce shields in the shape of sleeves, wraps, tubes and textiles so that all type of
cables can be shielded. Some cable shields need to be grounded at both ends, but it is usually best to ground at only
one end to prevent common-mode currents.
23. The housings themselves, i.e. the rack, the box, the enclosure, the metalized box, and the Faraday cage. They
constitute the main cover of the entire system and also the connection to the outside world. Housings are equipped with displays,
entries for power and signal lines, and cooling airvents.
24. Elements that can reduce the effectiveness of a Faraday cage:
Level III A - 26 32 Seams (Fig. 10)
Level III B 45 - Doors
Level III C 10 63 69 - Entries
Level III D 70 74 - Transparent displays
Level III E 79 - Ventilation panels
Level III F 64 69 - Cables for power supply
Level III G 65 - Cables for signals
Level III H 64 69 - Pipes for fluids, air, heating (Fig. 11)
Level III I 64 69 - Cables for optical connection

Figure 10. The pressing force on the panls of the
housing is minimized

Seams

25. It is important for the conductivity of the seam to be more or less
identical to that of the basic material that the cage is constructed out
of. Welding or soldering tends to works best, but for places that have
to be opened easily several mechanical connection methods are available: clamping, screwing, adhesive, sealing and sticking.

Summer 2017 * www.ElectronicsProtectionMagazine.com

Figure 11. Pipes of conductive material need insulating couplings

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Table of Contents for the Digital Edition of Electronics Protection - Summer 2017