July, 2015
www.us-
tech.com
EMI Shielding Caulk Cures Quickly and Is Paintable
Nick Pascucci, Parker Hannifin, Chomerics
cially for military radar shelters. Contributing to this overall shielding is an EMI shielding caulk developed by Parker Hannifin’s Chomerics Div. — a caulk that provides numerous mechanical benefits in addition to
S
hielding of electromagnetic interference (EMI) is critical to many electronic systems, espe-
applied in a temperature-regulated environment for proper results. Legacy caulks still tend to crack and corrode over time, requiring incon- venient field repairs. As an alternative to legacy EMI
caulks, Cho-Bond 1019 is a fast-cur- ing, paintable sealant with enhanced EMI shielding properties that can be applied over a more flexible applica- tion temperature range than legacy EMI caulks. The new EMI caulk combines metallic filler technology
with advanced polymer materials to achieve the improved performance.
Improved Shielding Needed EMI caulks for today’s military
applications should deliver improved shielding and anti-corrosion proper- ties, which are often achieved at high cost. Reducing the cure time can lower the cost of maintaining a large inventory of shelters to accommodate the long curing times. To achieve the better cure times
for the Cho-Bond 1019 EMI shielding materials, two non-silicone-based polymers were considered: a liquid poly thio ether (PTE) and polyure - thane (PU). Both polymers vulcanize to elastomers, which are resistant to water, solvent, fuel, and temperature and retain their elastomeric proper- ties over a wide temperature range. These materials will cure and be paintable in hours, not days. They can be applied at lower temperatures
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EMI shielding caulk provides EMI protection for military vehicle-mounted radar systems.
improved EMI shielding. The firm’s new Cho-Bond® 1019 material pro- vides reduced application time and excellent corrosion resistance. It is an electrically conductive caulking compound that is applied to the housing of electronic equipment for protection from EMI and electromag- netic pulse (EMP) energy. The caulk- ing compound is applied to the seams of aluminum enclosures, providing a shielding seal and a reliable Faraday cage around the sensitive electronic components within the enclosure, even for housings with warped seams.
The United States military has
used EMI caulk for decades on elec- tronic housings such as radar shel- ters, radar test facilities, and elec- tronic-warfare (EW) systems. For example,
the AN/MSQ-104
Engagement Control Station (ECS), which is the command and control unit of the Patriot Missile firing bat- tery, is housed in an EMI-shielded radar shelter mounted on a vehicle bed. The shielding caulk ensures protection from EMI even under con- ditions of shock and vibration. But systems such as AN/MSQ-104 have advanced over the years and are no longer adequately protected from EMI by legacy EMI caulks in the range from 150kHz to 18GHz, prompting the development of improved EMI caulking materials.
Legacy EMI Caulks Legacy EMI caulks are single-
component nonhardening com- pounds, such as silicone filled with silver-plated copper, which have been prone to corrosion. In the past, they have provided adequate EMI protection. But with newer electronic systems which are more sensitive to EMI, higher levels of EMI shielding are needed. Improvements are also needed to ease the application of EMI caulks, such as cure time, appli- cation temperature range, and "paintability." Epoxy-based paints applied to radar shelters will often not adhere to silicone EMI shielding compounds, and it can be necessary to apply a polysulfide environmental sealant over the caulk to make the surface paintable. The caulk and the polysulfide sealant each require seven days to cure and must be
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