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The Shocking Truth About Static Discharge Dangers

Tim Patel co-authored this blog.

As any first-year engineering student can tell you, electrostatic discharge (ESD) is an electrical transient that poses a serious threat to electronic circuits. The most common cause is friction between two dissimilar materials that causes electrical charges to build up on their surfaces. Because of the rapidly growing use of handheld and wearable consumer electronics, one of the surfaces involved is often the human body. In fact, people represent the largest ESD threat of all. A person will definitely notice pain from a sudden 6kV static discharge, but these discharges can be as high as 15kV. Although lower-voltage discharges sometimes go unnoticed, they can cause catastrophic damage to unprotected components and circuits.

Figure 1

The circuits highlighted in green may experience electrical overstress (over-current, ESD, or surge) and may require protection components to ensure reliable performance and/or to meet regulatory standards.

The circuits highlighted in green may experience electrical overstress (over-current, ESD, or surge) and may require protection components to ensure reliable performance and/or to meet regulatory standards.

ESD is characterized by fast rise times, high peak voltages, and currents up to 30A (per IEC 61000- 4-2, level 4), which can melt silicon and conductor traces. See Figure 1. However, the damage caused by ESD effects is not always so apparent. ESD can actually cause three types of damage:

  • Soft failures: Electrical currents due to ESD can change the state of internal logic, causing a system to latch up or behave unpredictably. They can cause corruption of data streams. Although this effect is temporary, it may slow down communications or require a system reboot in the case of lockup.
  • Latent defects: ESD can damage a component or circuit and degrade its function, even if the system continues to operate. However, this type of defect often progresses to a premature failure.
  • Catastrophic failures: ESD can damage a component to the point where it does not function as intended, or doesn’t work at all.

As IC dimensions continue to shrink, the opportunities for electronic circuit damage increase. Most ICs operate at low voltages and have structures and conductive paths that are unable to withstand the high currents and voltages associated with ESD transients. As higher-frequency communication devices are developed to transmit more information in less time, it becomes increasingly challenging to identify solutions that won’t compromise stringent signal integrity requirements at the higher data rates. The ESD suppressors used must have low internal capacitance so that data communication signals are not distorted.

IC designers add a limited amount of ESD suppression to their chips to help prevent damage during manufacturing and assembly processes. However, the level of protection that is added may not be sufficient to protect ICs and other semiconductor devices from ESD during actual use. Many electronic products, especially portable ones, are used in uncontrolled environments and can experience a charge buildup as users carry them. This energy can then be discharged to another device as the two are connected, usually when a user touches I/O pins on a cable connector.

End-product designers need to consider adding ESD suppressors to their circuits. They also need to consider potential coupling paths that would allow ESD to enter their equipment and circuits. These weak points identify areas that should be considered for ESD suppressor installation. Ultimately, designers need to select ESD suppressors with characteristics appropriate for their type of product, the component sensitivity, and the environment where it will be used.

Narrowing their choices down to the right ESD suppression strategy requires finding a balance between equipment protection needs and operating requirements, while taking the anticipated threat level into account. It’s also essential to consider potential suppression devices’ electrical characteristics, form factors, and package styles. Want to learn more about how to protect consumer electronics from ESD damage? View and download the Focus on Fundamentals Course materials: Staying Connected 24/7: Safeguard Consumer Electronics with Proper Circuit Protection.

9 comments on “The Shocking Truth About Static Discharge Dangers

  1. Davidled
    January 8, 2015

    All possible failure case could be simply protected in the protection circuit.  I never see any huge catastrophic failures in the development staging circuit. Engineer might minimize the use of extra protection component as much as possible. A proper protection circuit does not always require the protection component. Two topics might be separated in some cases.  

  2. Hughston
    January 10, 2015

    My original comments were as long as the article but I'll tone it down.

    The first thing I would do to prevent ESD failures is to give the product a lot of insulation resistance. If the ESD can't strike, it is less likely to cause a failure.

    Design the product well from an EMI standpoint. An ESD strike near the product can cause damage or upset. This type of immunity is sometimes tested by striking a vertical or horizontal plate near the product.

    A USB or power input needs a more robust protection because they have power transients and ESD.

    If there are outside connections like power, phone lines or USB that are connected during use, you can get more current in the ESD strike. An unconnected handheld device does not get a high current strike, but connect it to a charger and it gets more current.

    Something like a wall wart has high insulation resistance during the first ESD strikes but the insulation gets punched through over time by the strikes. Wall warts and other parts can wear out over time with ESD and you need to start over with a fresh product if you observe the ESD immunity going down.

    If ESD gets into your design it can jump around. You might see the burn tracks or just turn off the room lights and see where it goes.

    There is a lightning rod effect with ESD. Lightning likes pointy metal and so does ESD. The pointy metal can be a component lead, switch, trace or connector lead.

  3. fasmicro
    January 10, 2015

    >> Engineer might minimize the use of extra protection component as much as possible.

    That is coming from experience I guess. You do not need a lot of protection to make protection circuit. And the simpler the protection, the better.

  4. Vishal Prajapati
    January 13, 2015

    I have worked on one of the design of water dispensor which was solar and battery powered. It had the GSM modem which would be connected to MCU via serial communication. In between there was a MACX232 IC which was the main component to get failed in most of the outages.

     

    Due to no reason the MAX232 will stop responding. We later figured out that the chinise make was cheaper but unreliable which caused most of the failure due to ESD. Later on we replaced it with TI original ICs and problem got solved. Then after very few cases of ESD failure.

  5. TimLittelfuse
    January 13, 2015

    My opinion, with proper design methodology, you can reduce, but not eliminate ESD risk.  Environment is biggest component in the ESD link, and we have great difficulty controlling it.

     

  6. TimLittelfuse
    January 13, 2015

    Great, real life observations, 

  7. Vishal Prajapati
    January 16, 2015

    Hughston, I have seen the failure of the electronics components using ESD by at max malfunctioning of them or slight heating when run normally.

     

    But have never seen such an extreme case when the tracks are burnt. It is nice to know that you have pointed out the true situation which can be a result of ESD.

     

    And ya, I had never thought, how thoughtfull design is the USB connetor which has I/O pins shorter than the actual connector length, so the user will not accidently touch them.

  8. Hughston
    February 5, 2015

    Let me clarify my earlier comment.  I have not seen traces burned off the board by ESD strikes.  But, you will often see burn marks on the solder mask where the ESD jumped between traces or components on the board.  If you can turn off the lights in the test room you can often watch the ESD spark to see the path it takes in your design.

  9. webbpatj
    November 3, 2015

    Just because the electronics didn't fail right away, it doesn't mean that the MTBF (Mean Time Between Failure) of the circuit hasn't been decreased drastically.

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