Thermally Advantaged Small Chassis (TASC) Design Guide

Regulatory Considerations
E60781 15
4 Regulatory Considerations
The PC must meet a number of regulatory Safety, EMC and Ecology concerns. Specific
requirements for Information Technology Equipment vary somewhat by country,
however, the overall standards are somewhat unified and are based upon the
following standards: Note: Certain countries may require formal certifications and
many require a Declaration of Conformance (DOC) be placed in the manual or on the
box. In Europe the CE mark and a DOC is required for every computing device.
4.1 Electromagnetic Interference Radiation
The recommended vent size and free area ratio is not expected to pose a challenge
given current motherboard wavelength emissions for EMI performance. However
totals chassis design with appropriate grounding, seam and aperture features
contribute to EMI and are the responsibility of chassis designer to consider.
The Electromagnetic Interference (EMI) performance of a system is determined by the
degree of noise suppression designed into the system motherboard and the provisions
for EMI containment in the chassis design, including placement of internal subsystems
and cables. Requirements call for compliance to stringent electromagnetic
compatibility (EMC) limits such as the CISPR-22 European standards or the FCC “B”
United States standard. Open chassis requirements for board manufacturers suggest
that most EMI needs to be suppressed at the board level. The chassis, however,
should provide at least 6 dB of EMI attenuation or Shielding Effectiveness (SE)
throughout the spectrum. The goal of 6 dB assumes the board complies with FCC Part
15 (Open Box Test). Boards that have higher expected emissions will likely require
additional containment. These standards, along with higher processor and video
frequencies, call for additional chassis containment provisions. Basic design principles
have not changed, but as frequencies increase, the shorter wavelengths require more
frequent ground contacts and smaller apertures in the chassis design.
EMC Standards:
 47 CFR Parts 2 and 15 (USA)
 ICES-003 (Canada)
 EN55022:1998 (European Union Emissions)
 EN55024:1998 (European Union Immunity)
 Other International requirements based upon CISPR 22