Welcome to the Unboxing Tomorrow blog series on Arduino development.

Regardless of how long you’ve been using the Arduino and its many accessories, you probably have noticed the silvery anti-static packaging shipped with Arduinos and compatible gear. Depending on the supplier, you might also find the device shipped inside a blue or pink plastic bag, or embedded in black foam sheets. These each represent a different countermeasure against electrostatic discharge (ESD).

Clearly these are the tools for protecting your device from ESD during the storage and shipping phase of its journey. To fight ESD, engineers will use tools such as dissipating wrist straps, anti-static mats and flooring, and even specialized anti-static clothing. Yet many Arduino projects seem to run without a hitch, even if the user takes no anti-static precautions at all.

This of course begs the question: do Arduino users really need anti-static protection after the unboxing?

My short answer to this question, is “yes.” But to understand exactly why that is and what you are hoping to gain, let’s look at properties and effects of ESD.

Electrostatics in Context

Imaging you are tracking two independent projects been two engineers: Alice and Bob. Alice and Bob both have about the same level experience in electronics, the same level experience in programming, and they both follow the same methodologies—with one key difference. Alice uses ESD controls while Bob does not.

The project they have decided to build is a temperature data logger (similar to Datalogger.ino example included with the Arduino IDE). A build like this would probably involve a secure digital SD card and a matching Arduino shield, probably a thermistor to sense temperature, a precision thin-film or foil resistor to use as a reference, probably a real-time clock (RTC), and of course…the Arduino board itself.

One week into data logging, and things are uneventful. Clean signals. Clean data. Nice and boring all-around. And “boring” in this context is a very good thing.

One month in is no different. We simply have two data loggers logging data. Easy street.

But somewhere after the 2-month mark, things start to unravel for Bob’s data logger.
It starts as an occasional crash somewhere in the loop() portion of his code. It’s nothing that a manual reboot can’t handle, but no one is able to explain why it happens. The data logger now needs to be inspected on a daily basis to make sure it hasn’t crashed.

Some weeks later: a new problem. The temperature readings have suddenly shifted inaccurate readings for no apparent reason. Blaming the thermistor, Bob desolders it and then replaces it with an identical model. The original crashes have not yet been resolved, and now he’s lost over a full day of data in having to rework the equipment.

Weeks later: another blow. This time, the temperature reading is pegged at the max possible value, indicating an open circuit in Bob’s thermistor circuit. This time, he probes the precision resistor to find its resistance is out of range. Frustrated, Bob replaces that too: wondering why a high-reliability resistor with accuracy better than 1% would fail after just a few months of service. The data loggers still have to be checked every 24 hours, and worse still, the data needs to be inspected just as often due to the random measurement errors.

Electrostatic Discharge Latent Failure Summarized

So what happened here? In short: multiple failure modes, hardware instability, and degraded accuracy. And while we can’t be 100% certain without examining further, Bob’s devices is showing behaviors consistent with ESD damage.

As Alice, Bob, or anyone else walks over an insulating material like carpet or tile, that person’s body can build up an electrostatic charge through a process call tribocharging [1]. When you come in contact with a conductive object such as a door handle, you may feel short electric shock. This is ESD, the after-effect of tribocharging.

As Alice and Bob moved around their work area, negatively-charged electrons were transferred from the flooring material to their shoes. This left behind a positively-charged footprint.

Somewhere in their workflow, Alice and Bob reached out handle their data loggers. Alice’s electric charge would have been bled away into her grounded ESD wrist strap, grounded work mat, or other dissipative materials. Bob’s excess negative charge, however, went unabated. This leaves Bob radiating an electric field in all directions. Bob’s field will attract positive charges within the data logger, and if he happens to touch one of the data logger’s conductive surfaces, he will cause an ESD event.

Electrostatic discharge (ESD) is a common phenomenon, but it’s even more common than the public seems to realize. The human body can carry more than 10,000 V of ESD in a dry environment [2] [3]. And yet, ESD events below 3.5 kV can’t be detected by human senses [1]. Compare these high voltages to the absolute maximum operating voltage of 6 V that is specified by the ATmega328 or ATmega8U2-MU microcontroller (the “brains” of the Arduino Uno) [6]. While many devices like the NCP1117ST50T3G (the Arduino’s voltage regulator) have some ESD protection built-in, this protection is mostly applicable to the fabrication and packaging process; not for everyday handling by humans.
Due to the damage caused by ESD, billions of dollars are lost per year. Worse: as electronic devices become smaller, the harm that ESD can inflict is becoming more and more severe [4].

Damaged but not Destroyed

So why do electronics continue to work perfectly even if you don’t use anti-static measures?

Firstly, who says they are still working perfectly? Many devices of this scale lack a built-in test (BIT) that can show us if a working device is truly a healthy device. This means that the many damage modes of an ESD strike can realistically go unnoticed by the user.
Secondly, a device that has been exposed to ESD can also be destroyed by conditions that would normally be safe for healthy device [5].

What happened to Bob’s data logger in this scenario is a prime example of latent failure.
Unlike other failure modes, latent failures can go undetected for large amounts of time before making their presence known. Latent effects are especially insidious in the problem-solving process, since we generally require immediate feedback to understand a cause and effect relationships.

Summary

So, do Arduino users really need anti-static protection after the unboxing?

To put it succinctly, the research points us to an emphatic “yes.” While there are no real guarantees when it comes to ESD and related effects, you can consider these tools an extra layer of defense against lost time, labor, materials, and other resources.

The alternative is using no ESD protections at all: thus exposing your next project to difficult-to-diagnose latent failures and reduced service life.

Conversely, the downside to using ESD controls is obvious: having to use them. Besides being mildly bothersome to deal with, you should take special care purchase quality equipment and test it regularly per the suppliers recommendations. But the reward is getting to spend more of your time and resources doing what you love, and less time hunting for elusive, non-reproducible ESD-induced problems.

Relevant Links

Arduino UNO r3 Schematic:
https://www.arduino.cc/en/uploads/Main/arduino-uno-schematic.pdf

ATmega8U2 ATmega16U2 ATmega32U2 Datasheet:
http://ww1.microchip.com/downloads/en/DeviceDoc/doc7799.pdf

ATmega48A, ATmega48PA, ATmega88A, ATmega88PA, ATmega168A, ATmega1688PA, ATmega328, ATmega328P datasheet:
http://ww1.microchip.com/downloads/en/DeviceDoc/ATmega48A-PA-88A-PA-168A-PA-328-P-DS-DS40002061A.pdf

References

[1] C. R. Paul, “System Design for EMC,” in Introduction to Electromagnetic Compatibility, 2nd ed., John Wiley & Sons, Inc., 2006, pp. 753 – 775.
[2] A. Amerasekera and C. Duvvury, “ESD,” in Silicon Integrated Circuits, New York, John Wiley & Sons, 2002.
[3] J. J. Liou, “Introduction to electrostatic discharge protection,” in Electrostatic Discharge Protection, Advances and Applications, Boca Raton, FL, USA, CRC Press, 2016, pp. 1-11.
[4] L. Jin and C. Yongguang, “Characteristics and distribution of electromagnetic field caused by electrostatic discharge,” High Voltage Engineering, vol. 38, pp. 435-443, 2012.
[5] G. Groos, D. Helmut and G. Wachutka, “The Latent Failure Issue Seen from the Other Side: Normal Operation after ESD Induced Degeneration of Devices and Systems,” in 40th Electrical Overstress/Electrostatic Discharge Symposium (EOS/ESD), Reno, NV, USA, 2018.
[6] Arduino, “Arduino UNO Reference Design,” [Online]. Available: https://www.arduino.cc/en/uploads/Main/arduino-uno-schematic.pdf. [Accessed 1 Aug. 2019].

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