Arduino Uno ESD ruggedness

Question

I want to route one of the Arduino's digital output pins out of a device, to interface with other instruments via a several meter long coax cable. Typically, I would implement measures against ESD for such a use case. However, I am wondering if this is redundant, because the bare Arduino boards don't seem to care much about ESD. The question is somewhat academic I admit, because I have not much to lose when simply placing the ESD protection anyway. But I am interested why this is not always seen.

The Arduino Uno R4 has no additional ESD protection components on its board. The digital pins are directly routed into the microcontroller R7FA4M1AB3CFM. The datasheet for the latter indicates no special ESD ruggedness. Searches for "kV", "HBM" or "61000" turned up nothing. A search for "ESD" only revealed a note, that ESD is bad.

The absolute maximum ratings do not indicate any special ruggedness either. A maximum fault current is not given, so I assume it to be minimal:

Still, I observe people handling the board with no special care, touching pins, with power on or off, easily generating voltages of 100s or 1000s of volts and the board survives this without issues.

So ESD seems to be no problem for the Arduino to such a degree that the makers of Arduino didn't bother to implement onboard ESD protection on a product that is obviously mass-produced. So I have an inner conflict: my intuition to require ESD protection for my use case and my other intuition to trust the careful design choices of a reliable mass-produced Arduino board.

Is extra ESD protection needed for my use case? If so, why is it not needed for other use cases like millions of students tempering with it on their fiber carpet?

Answer 1

ESD rating isn't a guarantee of failure beyond a threshold. It is a guarantee of survival below a threshold.

Or, even more specifically, it might be a sampling point, wherein some articles have been tested at such-and-such level, and seemed to survive. I'm not sure about IC ratings (I don't have the base standards), but suspect they're done on a design-assurance level; equipment is certainly tested on such a sampling basis however (i.e. you run one unit through EMC testing and it passes or fails). Perhaps someone involved in IC design can offer context on this.

Anyway, I've seen plenty of things get zapped by way more than they deserve to handle, and, at least without digging closely (monitoring supply consumption / pin leakage, testing pin characteristics like exact ESD diode voltages, recovery time, hFE to adjacent pins / through supply, etc.), they at least seem to continue functioning. But momentary function is not a guarantee of continued function, or of robustness for every part (of the same type) ever produced.

Intermittent operation is a typical consequence. Sometimes a part is damaged, but recovers over time; others survive but later fail. Maybe it comes and goes. Diffusion of atoms in the affected zone can turn either way, and partially melted or vaporized conductors can migrate, break or reform. Most often it survives or doesn't, but there are random partial cases and you don't really know for sure.

If a chip doesn't specify ESD ratings, it's possible it's a 1kV default, specified in a rarely-seen (if you're not a manufacturer) JESD, JEDEC or other standard. It might also be specified in a common document somewhere; check the quality section perhaps?

I would just as well decline to use a part that doesn't specify its ESD level. Not that that's helpful to users of such a board...

As for why they didn't? Expense, I'm sure. If the board is cheap enough, who cares. Arduino stuff I suppose I would consider somewhat disposable. It's also arguably development materials to be operated by authorized technicians and therefore not required to meet ratings. (As commodity items, they are still CE rated, though I haven't checked what they've actually rated them for; this will be, in part, in their filings/disclosures.)