Design Checklist for Electromagnetic Compatibility
(Summary from EMC for product engineers by: Tim Williams)
Compiled and reproduced by: Rodelio P. Barcenas
DON BOSCO TECHNICAL COLLEGE

Many factors must be considered when looking at the EMC aspects of a design, and it is easy to overlook an important point. This checklist provides for you to assess your design against as it proceeds.

• Design for EMC from the beginning; know what performance you require
• Partition the system into critical and non-critical sections
  
  • Determine which circuits will be noisy or suceptible and which will not
  • Lay them out in separate areas as far as possible
  • Select internal and external interface points to allow optimum common-mode current control

• Select components and circuits with EMC in mind
  
  • Use slow and/or high-immunity logic
  • Use good RF decoupling
  • Minimize signal bandwidths, maximize levels
  • Provide power supplies of adequate (noise-free) quality
  • Incorporate a watchdog circuit on every microprocessor

• PCB Layout
  
  • Ensure proper signal returns; if necessary, include isolation to define preferred current paths
  • Keep interference paths segregated from sensitive circuits
  • Minimize ground inductance with thick gridding or ground plane
  • Minimize enclosed loop areas in high current, high di/dt or sensitive circuits
  • Minimize surface areas of nodes with high dv/dt
  • Minimize track and component leadout lenghts

• Cables
  
  • Avoid parallel runs of signal and power cables
  • Use signal cables and connectors with adequate screening
  • Use twisted pair if appropriate
  • Run cables away from apertures in the sheilding, close to conductive grounded structures
  • Avoid resonant lenghts where possible, consider damping cables with ferrite suppresors
  • Ensure that cable screens are properly terminated to correct type of connector

• Grounding
  
  • Design and enforce the ground system at the product definition stage
  • Consider the ground system as a return current path, not as 0V reference
  • Ensure adequate bonding of screens, connectors, filters, cabinets, etc.
  • Ensure that bonding methods will not deteriorate in adverse environments
  • Mask paints from any intended conductive areas
  • Keep earth leads short and define their geometry
  • Avoid common ground impedance
  • Provide a "clean" ground area for decoupling all interfaces

• Filters
  
  • Optimize the mains filter for the application
  • Use correct components and filter configuration for I/O lines
  • Ensure a good ground for each filter
  • Apply filtering to inteference sources, such as switches or motors
  • Pay attention to the layout of filter components and associated wiring or tracks

• Shielding
  
  • Determine the type and extent of shielding required from the frequency range of interest
  • Enclose particularly sensitive or noisy areas with internal shielding
  • Avoid large resonant apertures in the shield, or take measures to mitigate them
  • Ensure that separate panels are well bonded along their seams

• Test and evaluate EMC continuously as the design progresses

(Summary from EMC for product engineers by: Tim Williams)
Compiled and reproduced by: Rodelio P. Barcenas
DON BOSCO TECHNICAL COLLEGE