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I keep reading that one shouldn't have traces close to the edge of the board and am curious as to whether there is an electrical reason behind this or if it's a mechanical issue (like when they cut the pcb, it might somehow rip up the traces)?

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  • \$\begingroup\$ There's a couple of possible reasons. Some context would be helpful. \$\endgroup\$ – Matt Young Dec 6 '15 at 4:02
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    \$\begingroup\$ Obviously your electrons are going to fall out \$\endgroup\$ – PlasmaHH Dec 6 '15 at 9:54
  • \$\begingroup\$ Traces at the edge of the board will have fields not contained in PCB level. There will be outside radiation because of this \$\endgroup\$ – user19579 Dec 9 '15 at 11:33
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From Sunstone (my favorite high quality short run PCB shop)...

A very high percentage of orders are placed on hold due to insufficient board edge to copper clearance.

We care about exposed copper at the board edge for a couple of reasons.

  • Copper can tear when it is routed, leaving strings that can short to adjacent layers.

  • Exposed copper can wick solder in a wave solder process, causing shorts at assembly.

  • Exposed copper at the board edge can make contact with your product chassis, causing a short to ground and/or risk of electrical shock.

So, both mechanical and electrical!

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    \$\begingroup\$ This is complete enough I'm just going to tack on: digital signals around the edge of your board can radiate excessively because there isn't enough ground plane coverage for them and the current density builds up in the ground plane near the board edge. \$\endgroup\$ – Daniel Dec 6 '15 at 4:30
  • \$\begingroup\$ @Daniel: Can you explain why we need ground plane beneath the trace to reduce radiation? I mean if you can explain that with field lines? \$\endgroup\$ – abhiarora Oct 18 '17 at 7:26
  • \$\begingroup\$ @abhiarora That is too complex to address in a comment. You should ask a new question. \$\endgroup\$ – Daniel Oct 23 '17 at 23:33

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