Ni/Al filled elastomer gaskets combine shielding effectiveness with galvanic compatibility
11 May 2010
Chomerics Europe has introduced new EMI shielding materials that use low transfer impedance Nickel aluminium (Ni/Al) particle filled elastomers to give high levels of shielding effectiveness. Available as moulded, extruded and form-in-place (FIP) gaskets, the new materials also offer high stability and excellent galvanic compatibility with aluminium. This means that pitting due to galvanic erosion is significantly reduced compared with applications that use Silver Aluminium (Ag/Al) filled elastomers.
The high reliability levels of the new gaskets helps reduce field service and warranty needs giving total cost of ownership savings in the region of 30 to 40%. The materials can also overcome the requirement to apply Ni or Tin (Sn) plating to aluminium flanges and housings, and may alleviate the need to incorporate secondary outboard non-conductive gaskets, and complicated partial flange painting operations.
CHOFORM 5560 is the FIP version of the new material. Applied using dispensing technology, it can be placed on narrow flanges and achieves shielding effectiveness of 80 to 115dB. Narrow flanges can allow for smaller overall package sizes or increased space for PCBs. The material has low compression set for long-term sealing and is extremely soft; this lowers closure force requirements and in some applications may eliminate the need for fasteners and more rigid housings.
CHO-SEAL 6502 (silicone) and 6503 (fluorosilicone) are available as moulded or extruded gaskets, they can also be over-moulded directly onto components to reduce costs and simplify assembly. Both materials have a shielding effectiveness of over 100dB. Parts can be moulded with cross sections specifically designed to allow low closure forces to be used.
All three materials have a maximum operating temperature of 125°C. CHO-SEAL 6503 also complies with MIL-DTL-83528C for fluid immersion.
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