PCB EMC Control
- Second Line of Defense -

The most commonly acknowledged design approach to EMC compliance design is at the printed circuit board (PCB), or sometimes called a Printed Wire Board (PWB), level. The design is the most critical in the process, since EMI problems on a PCB cause EMI problems on cables, harnesses and at the system level.

Following are some tips and things of which to be aware:

• Layout design is critical to EMI Control:
• Component placement and orientation.
• Trace, power & ground-plane geometry.
• Signal paths & termination techniques
• Power & noise filtering.
• PCB's can resonate at critical frequencies, which may exacerbate EMI.
• Differential Mode EMI on Signal Traces:
• Loop antennae can radiate and pick up noise.
• Common Mode EMI on Signal Traces:
• Line antennae can radiate and pick up noise.
• Ground & power fluctuations can radiate noise.
• PCB-level circuit simulation techniques are useful to gain a ballpark knowledge of where your PCB layouts can be optimized for compliance.

Cable EMC Control
- Third Line of Defense -

Interconnect systems (cables & harnesses) are the most common avenues for EMI to exit or enter the PCB and system. Appropriate signal drivers & receivers, cable design and grounding techniques can help reduce EMI effects here.

Following are some tips and things of which to be aware:

• Cables disrupt EMC integrity of enclosures.
• INTRA-BOARD cables:
• Create antennae to radiate & pick up noise.
• INTER-BOARD cables:
• Create antennae to radiate & pick up noise.
• Create ground potential issues, thus inter-system EMC problems.
• Cables can resonate at critical frequencies, which may exacerbate EMI.
• Cable simulation techniques are useful to gain a ballpark knowledge of where your cable designs can be optimized for compliance.