ESD or Electrostatic discharge is the rapid spontaneous transfer of electrostatic charge induced by a high electrostatic field. The electrostatic field is most commonly generated by triboelectric charging (the contact and separation of materials). We can often see and feel these electrostatic discharges on a dry cold winter’s day as we touch something (or someone) and the charge we have built up (for example walking across a carpet) causes a spark to discharge. ESD damage can occur at much lower voltages than a person can detect as the minimum ESD voltage that can be detected by a person is 2000V! As illustrated in the chart below that is already much higher than some devices can withstand.

Fig: 1. ESD sensitivity of components. (n.d.). Retrieved from: http://www.electrostatics.net/ESD_Guide/technical/ESD_sensitivity.htm

Device ESD Withstand Voltage Sensitivity Chart

Figure 2 below illustrates how much electrostatic voltage can be accumulated and discharged depending on humidity.

Fig 2: Typical Electrostatic Voltages Retrieved from: https://www.esda.org/esd-overview/esd-fundamentals/

For electronic devices ESD causes three types of failure modes:

1. Catastrophic damage – damage or failure is immediate and part needs be replaced.
2. Latent damage (no initial sign of damage) after ESD discharge but damaged device eventually fails down the road or works intermittently/erratically (needing replacement).
3. Functional disruption such as unexpected resets, latch ups or upsets during operation right after ESD discharge but can be recovered when the device is reset or power cycled.

The susceptibility of electronics to ESD damage increases as their density increases (and the smallest transistor features size decreases).   Like other highly integrated processors, the Qualcomm Snapdragon and its high-density system components such as high capacity SDRAM and eMMC can be particularly susceptible to ESD damage.

Various external peripheral busses on the Open-Q development kit carrier boards, such as the integrated USB, SD and audio, are designed with standard ESD protection, but this doesn’t obviate the need for careful handling procedures, especially during transport. Also, other high speed bus connectors (such as CSI, DSI, MIPI and high-speed BSLP serial) are susceptible to ESD damage. When employed in end-user applications such as commercial IoT devices, proper design of your product’s enclosure and customized carrier board will ensure only protected connectors are exposed to hazard.

To prevent damage to your Development Board from ESD always ensure the following precautions are taken:

1. Always store and carry your development kit Printed Circuit Board Assemblies (PCB) when not in use in an electrostatic safe container or electrostatic safe bag as shown below.

2. Before removing the development board from the ESD Shielding bag, ensure you are properly grounded with an ESD wrist strap or foot strap and that your work space has an electrostatic safe mat or work surface as illustrated in the figure below.

. Unless your development board is put inside of a protective enclosure it should only be handled on an ESD safe work area where the personnel are grounded. The development boards only have ESD protection build-in on the external interfaces such as connectors, headers and ports. Do not handle the development board or touch components on the board without being properly grounded first.

4.Keep plastics (bags, tools, plastic covered 3 ring binders and clipboards, containers etc.), polystyrene products (Styrofoam) and synthetic clothing several feet away from your development board as they carry sufficient electrostatic charges to damage electronic components. Only plastics and hand tools that have been specifically designed to be ESD safe (will state it on the item or will have the ESD logo stamped on it) can be used around ESD sensitive devices such as your development board.

Author

Alec Ho is a design engineer on Lantronix’ Snapdragon hardware team.  He has over twenty years’ experience in the electronics industry, specializing in telecommunications.   His work with Lantronix and previous organizations such as VIAVI involves in schematic capture, PCB layout, system verification, component sourcing, and equipment specification and calibration.   He has previously been a dedicated EMC and ESD engineer for consumer product manufacturers including Nokia and Vtech Engineering, where he had responsibility for EMC and ESD design guidelines, industrial standards testing, and training.