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I have a PCB in the field that is put in an enclosure box and is placed on a pole in an open environment. My question is, if the PCB does not have the power supply connected, can ESD still damage the PCB or any of the sensitive components?

Please correct me if I'm wrong, but just like normal voltage signals that go from higher potential to lower potential, ESD would try to find the smallest path to ground. So, even in the worst case if a lightning bolt does hit the pole, the charge would rather travel straight towards the ground than touching the PCB board (not powered up).

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    \$\begingroup\$ Yes, ESD can damage unpowered boards. Quite easily, in fact. \$\endgroup\$ – Hearth Dec 17 '19 at 17:51
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    \$\begingroup\$ A lightning bolt didn’t have any trouble travelling the several miles to the pole through air did it? \$\endgroup\$ – Andy aka Dec 17 '19 at 18:03
  • \$\begingroup\$ Yep. No escape. \$\endgroup\$ – DKNguyen Dec 17 '19 at 18:03
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    \$\begingroup\$ Without power, ESD can still destroy your chips, but at least it won't make your CPU crash, so there's always that... \$\endgroup\$ – bobflux Dec 17 '19 at 19:57
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    \$\begingroup\$ Why do you think most electronic components are packaged in ESD bags? They certainly aren’t powered while still in the box. \$\endgroup\$ – jcaron Dec 18 '19 at 3:13
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My question is, if the PCB does not have the power supply connected, can ESD still damage the PCB or any of the sensitive components?

ESD doesn't need a pathway back to ground to be destructive, almost everything looks like a conductor when voltages are in the thousands of volts. Once an ESD event gets started it causes a current avalanche and materials (even air and insulative materials) start to break down and become conductive and destroys anything in its current pathway.

enter image description here
Source: https://nepp.nasa.gov/index.cfm/6095

The picture above shows a capacitor on an IC, which has a layer of insulation between it and the other side of the capacitor. The ESD event blew right through the insulator.

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    \$\begingroup\$ Voltage Spike, did you do that to the IC in the picture? Or was it one of your cousins? \$\endgroup\$ – Michael Karas Dec 17 '19 at 19:15
  • \$\begingroup\$ @MichaelKaras Actually our manufacturing unit keeps sending me broken boards, I've dencapsulated a few of them to try and prove that it was ESD to show them they need to have ESD control, but I don't have an electron microscope. So I wasn't able to prove to them that it was ESD \$\endgroup\$ – Voltage Spike Dec 17 '19 at 19:33
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Yes, it can. Standard practice at our facility is to keep boards, assemblies, components, etc in ESD bags or containers. When a board is handled outside of the bag/container, we always wear ESD wrist straps and lab coats. This includes when installing a board into a chassis.

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