There are many reports in reddit that people have gotten their PCB damaged due to ESD just by touching the metal case.
Some have suggested that connecting the keyboard case and the switch plate to the shield of the USB solves ESD issues that are caused by touching. Anyone knows if this really works without issues?
I’m not an electrical engineer, but I think it really does depend on the implementation of the PCB. From my understanding, connecting a conductive plate and case to USB shield will significantly hinder the ability of a transient to reach sensitive components along any shared connections (people usually just tie shield to ground or leave it isolated), but, if the reports are true, the voltage may reach the circuit regardless. Additionally, the damage to the components may have occurred through some other means that is less obvious (a short elsewhere on the PCB, bad cables, power management issues, etc.). Are you sure ESD is the culprit?
In short, while ESD chips do function by diverting excess electrical energy to ground in line with your logic, there is no such shortcut to arrive at protection. The design of the board itself needs to account for transients.
Thank you for the response. Here are some of the complaints I mentioned.
_https://www.reddit.com/r/MechanicalKeyboards/comments/aup22m/how_do_you_deal_with_esd/
_https://www.reddit.com/r/MechanicalKeyboards/comments/8qd975/any_60_pcbs_with_staticshock_measures/
_https://www.reddit.com/r/MechanicalKeyboards/comments/87l6hd/static_electricity/
_https://www.reddit.com/r/MechanicalKeyboards/comments/do9366/aluminium_cases_and_electrostatic_discharge_esd/
@hadi mostly got it, usually you would put some sort of protection (TVS diode, zener, etc) on data lines that are exposed to the outside, but that’s mostly for if you were to touch the connector or something. What could make a lot of difference is how the metal case and conductive plate are connected to board and earth ground, grounding the usb connector shield can help, but there needs to be a path from the case/plate to that earth ground through the cable. This can be done either directly (less safe) or through a resistor and cap (more safe, how IOs are typically done). There are definitely some bad ones out there, but I’ve only ever killed one keyboard due to ESD, and it was especially poorly designed, but then again I live in a place where it’s not much of an issue in general.
I would look at if the data lines are protected (so easy to do, I’m glad it’s becoming more standard) and then what the mounting you plan on using is and if the screws (if any) that go to the case are grounded.
Poor USB cables can cause issues with even the best designed boards. A lot of the “custom” cables in the keyboard scene are poorly made and not even close to USB spec. A proper USB cable should have 5 lines. V+, ground, D+, D-, and a drain line. Many custom cables, especially those with aviator connectors skip the drain line.
Thank you for the detailed response.
In layman’s terms I would think that the wire from the switch plate and the case to the USB shield should be less as obstructive as possible. I, without expert knowledge, would have thought that a resistor and a cap would obstruct the path of an ESD shock towards the USB shield. But you mentioned that it is safer to do it through a cap and a resistor. How does it work?
Usually you would use a high voltage 0.1uF cap (like 2kV), that will pass big transients, and then the resistor will prevent charge build up
Some say that circuit ground and the chassis ground should be separated. But what we talked about is contrary to that. And DZ60-V2 Hot-swap for example has contact pads at mounting post screw holes. But not sure what they are connecting to the chassis and whether they are keeping the circuit ground separate from the chassis ground and USB shield.