Are ESD wrist straps, gloves and table mats safe to use while handling a live PCB or a turned on Raspberry Pi, for example?
What I intend is to protect the components against static discharges.
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2\$\begingroup\$ safe to use <-- for the human or for the circuit board? \$\endgroup\$– Andy akaOct 5, 2022 at 12:06
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\$\begingroup\$ For the circuit board \$\endgroup\$– fabiopsOct 5, 2022 at 12:10
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\$\begingroup\$ A RPi is low voltage so you are safe anyway, but please measure that your wrist strap has 1 Mohm series resistance. If yes, you are good to go. \$\endgroup\$– winnyOct 5, 2022 at 12:21
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\$\begingroup\$ For hobbyist purposes, you really don't need anti-ESD equipment... that's for production lines. Using common sense will get you quite far, like... touch the edges of the PCB when you grab it instead of poking your fingers directly at the components. Don't wear a fleece jacket or pet a cat while handling the PCB. And so on... \$\endgroup\$– LundinOct 5, 2022 at 13:43
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\$\begingroup\$ @Lundin I agree, same thing with seat belts. Only necessary for professional drivers who are on the road a lot. A hobbyist driver can just use common sense to avoid accidents. \$\endgroup\$– pipeOct 5, 2022 at 21:09
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2 Answers
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Yes it is safe and the preferred approach.
ESD wristbands, table mats, etc. are usually connected to protective earth through a 1 MΩ resistor.
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\$\begingroup\$ What if the table mat is antistatic silicon and doesn't have a connection to ground? And in the case of the gloves, if they have a surface resistance of <10Mohm and also no connection to ground. Is my board safe of short circuit if i touch the solders or if the solders are touching the mat surface? \$\endgroup\$– fabiopsOct 5, 2022 at 12:10
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1\$\begingroup\$ @fabiops I guarantee you it's not silicon, it's silicone. There's a difference. And it is not safe unless there's a connection to ground (or rather, a connection to some fixed potential that the circuit board is also connected to. Ground is easiest.) on the antistatic mat and your ESD wristband. \$\endgroup\$– HearthOct 5, 2022 at 13:02
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\$\begingroup\$ Just to add that we handle, troubleshoot, & probe powered up systems all the time with proper ESD protection. Sometimes the ESD mat is not used, as in the case when an assembly is mounted on a handling fixture of some sort. In that case the ESD strap is connected to earth ground, sometimes through the fixture. \$\endgroup\$– SteveShOct 5, 2022 at 13:23
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Yes: boards that are low-voltage safe to handle without ESD protection are safe to handle with it.
The ESD protection mats, gloves etc. are made of higher-resistance material. So they won't conduct enough current from the low voltage to dissipate damaging power in the circuit.
However, the operation of circuits using very high resistances, like 100's kohms, can be affected by putting a gloved finger on them. That won't result in damage, just a change in performance.
An extra effect is added by the connection of the ESD protection to ground through the 1 Mohm or so resistance used by ESD earthing equipment.
It's therefore good practice to not operate boards that are lying flat on an ESD mat, for example. It doesn't mean they will start behaving differently. Instead, it rules out the possibility that they are ever behaving differently. Hence good practice, not necessity.
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\$\begingroup\$ When I read the question, this was what I was wondering about: In order to protect from ESD, the mat surface must be somewhat conductive, I suppose -- or are the layered mats generally designed with a thin non-conductive surface, and the conductive layer under it is sufficient to drain any charges from the top layer? Because I remember an incident when we ESD safe packaging material as a work surface, and that did change the behavior of the circuit, which took us a while to discover. \$\endgroup\$ Oct 6, 2022 at 8:29