Electronics Protection - Summer 2017 - 12

Feature
Holland continued from page 11

Prevention of Corrosion

33. In the design stage it is important to specify the environment; it
makes a difference whether the construction has to be able to withstand only humidity, or exposure to water (possibly even salt water),
fog, or condensation, e.g. during transport.
34. If the metal of the housing is sensitive to corrosion, a finishing
of e.g. nickel and chrome can help the contact surface maintain the
required conductivity. Materials like aluminium and zinc-plated steel
develop an oxidation layer, which reduces the corrosion process but is
less conductive.
35. Galvanic Corrosion: Even when the materials of the housing withstand corrosion well, it is important that they work together not only
with one another but also with the gasket (Fig. 14).

Figure 14. Galvanic corrosion table

36. Sea/Water Environment: In a situation where the galvanic values of the gasket and the housing material differ
more than 0.3 Volts in a salty environment, or 0.5 percent in an environment with just water, galvanic corrosion will
occur. Even at a distance of 10 km from the sea, the atmosphere may be as salty as right on the coast. So the appropriate gasket material has to be chosen, see
gasket selection graph.
37. Around the bolt holes should be sufficient
space for a water seal. Water should never reach
the EMI gasket or the construction via the bolt
holes. Alternatively extra water sealing can be
applied around the the bolts in the form of rings
(Fig. 15).

Figure 15. (left) EMC/IP gasket example. Figure 16. (right) Combined
gasket(waterseal combined with EMC)

38. For small parts, where there is less space a gasket out of e.g. electrically conductive rubber can be used. These
are available in profiles and plates , which can be cut accurately to the required dimensions.
39. For bigger parts it can be more efficient to use a combined gasket. An EMI gasket with a water seal made of neoprene, silicone or EPDM rubber (Fig. 16)
40. Neoprene has quite good flame retardant properties and can handle temperatures of -40°C to 100°C. EPDM rubber can withstand temperatures up to 120°, making it suitable for the engine compartment of cars. Silicone rubber is
used for temperatures up to 220°C; it can be sterilized for medical applications and is soft.The rubbers can either be
made in the shape of a foam or mousse or as a solid product.

Rules of Thumb for Gasket Choice,
Depending on the Type of Enclosure

41. Very small construction, (smaller than 150 by
150) grooves, casted, moulded or machined: conductive profiles, o-ring or cut gasket out of highly
conductive rubber are suitable (Fig. 17).

Figure 17. (left) Groove construction with conductive o-ring gasket.
Figure 18. (right) Solutions for medium size constructions.

42. Small construction, (about 200 by 200 mm) multi-shield gasket, consisting of metal wire from top to bottom
though a soft silicone rubber with a thickness of 2 to 3 mm are suitable (fig. 18).
43. Medium size construction: zinc-plated steel/metal: standard shield, neoprene foam with water seal, minimum
width about 4 mm and thickness 2 to 3 mm (fig. 19).
12

Summer 2017 * www.ElectronicsProtectionMagazine.com


http://www.ElectronicsProtectionMagazine.com

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

Editor's Choice
Smart Electronic Adhesives for Microelectronics – Enabled by Low Viscosity Nanocomposite Materials
Sheilding Tips and Tricks
Digital Analysis Brings Convenience and Accuracy to Power Measurement
Enclosures
Thermal
EMI/EMC/ESD
Power
Hardware
Industry News
Electronics Protection - Summer 2017 - Cover1
Electronics Protection - Summer 2017 - 2
Electronics Protection - Summer 2017 - Editor's Choice
Electronics Protection - Summer 2017 - Smart Electronic Adhesives for Microelectronics – Enabled by Low Viscosity Nanocomposite Materials
Electronics Protection - Summer 2017 - 5
Electronics Protection - Summer 2017 - 6
Electronics Protection - Summer 2017 - 7
Electronics Protection - Summer 2017 - Sheilding Tips and Tricks
Electronics Protection - Summer 2017 - 9
Electronics Protection - Summer 2017 - 10
Electronics Protection - Summer 2017 - 11
Electronics Protection - Summer 2017 - 12
Electronics Protection - Summer 2017 - 13
Electronics Protection - Summer 2017 - 14
Electronics Protection - Summer 2017 - 15
Electronics Protection - Summer 2017 - Digital Analysis Brings Convenience and Accuracy to Power Measurement
Electronics Protection - Summer 2017 - 17
Electronics Protection - Summer 2017 - 18
Electronics Protection - Summer 2017 - 19
Electronics Protection - Summer 2017 - Enclosures
Electronics Protection - Summer 2017 - 21
Electronics Protection - Summer 2017 - Thermal
Electronics Protection - Summer 2017 - 23
Electronics Protection - Summer 2017 - EMI/EMC/ESD
Electronics Protection - Summer 2017 - 25
Electronics Protection - Summer 2017 - Power
Electronics Protection - Summer 2017 - Hardware
Electronics Protection - Summer 2017 - Industry News
Electronics Protection - Summer 2017 - 29
Electronics Protection - Summer 2017 - Cover4
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