Electrostatic discharge (usually known by the acronym ESD) is an electric phenomenon that causes a current to flow suddenly and momentarily between two objects of different electrical potential. Examples of this phenomenon are many, but maybe the most visual example is the occurrence of lightning.
According to our good friend Wikipedia:
Lightning is a sudden electrostatic discharge that occurs typically during a thunderstorm. This discharge occurs between electrically charged regions of a cloud (called intra-cloudlightning or IC), between two clouds (CC lightning), or between a cloud and the ground (CG lightning).
As damaging as you can imagine lightning can be, damages due to electrostatic discharge also frequently occurs in very familiar devices — electronic gadgets and computers. Usually these devices have sensitive electrical circuits so that when a sudden gush of electricity flow into their system one or more of the circuit’s components may be damaged rendering the whole circuit and the device inoperable. handled and transported on metal supports.
Like the example of how lightning can occur above, ESD (Electrostatic Discharge) in an electronic device can occur in the following situation:
- Direct electrostatic discharge to the device.
- Electrostatic discharge of the device.
- Discharges induced by the field.
In electronic test laboratories problems due to ESD is very real so lab managers and employees treat the subject very delicately. Not only can it damage very expensive test equipments, ESD can also damage the device being tested. In the world of electronic compliance testing, even a minute damage is very problematic since this can change the test results rendering the whole test invalid without you even knowing it.
Of course, if the value is unusually diverging from the value that the tester expects, the tester may suspect damage to either the test equipment or the DUT (device under test) and re-calibrate the test apparatus. But when the value is not so far from the one that the tester expected, he or she may decide that the result is valid although this might not be the case. This is true for when the DUT is the one that has been damaged. It would be difficult to debug the damage especially if the tester is not involve in the designing and development of the DUT.
As with many troubles and damages, the most effective way to curve future damages through ESD is by active and vigilant prevention. The following are the most common devices used to prevent damage through ESD:
- Anti-static wrist strap, also called ESD strap, is made of an insulated material with a wire connected to specifically drain away the electrical charges from the human body (the tester) before and when touching the test equipment and DUTs. You wrap the strap part to your wrist and clip the other end of the strap to the ground. This prevent accumulation of static electricity from the body by always flushing it down to the “ground”.
- Antistatic bags: These bags should be used when storing or sending electronic equipment, because they keep the charges away from the equipment. The anti-static bags use the Faraday Cage effect to keep electrical charges to penetrate the inner part of the bag, which protects the electronic device that is stored inside it.
- Antistatic mats or blankets consist of an insulated material and two cables with wire clips at each end. The mat should be spread on a flat surface and place one of the clips on the nearest sensitive equipment ground. This transfers the load of electronic equipment placed on the carpet to the ground. The effect is much like the anti-static wrist strap, but this instead of targeting static electricity from the body, these mats target electrical loads from the equipment themselves.
- Anti-static footwear or the ESD footwear diverts the electrostatic discharge accumulated in the body to the outside. Again the idea is the same as anti-static wrist strap, but since the slippers are always worn in the work lab, it helps in prevention. Sometimes testers forget to put on the ESD strap before touching the devices, so its nice to have the slippers on just in case.
To sum, ESD is real and present danger inside all electrical test laboratories. The damage that ESD can do to test equipment post a very serious problem in test labs since even slight damage affects the validity of test results. Damage due to ESD is difficult to debug especially if the one that is damaged is the DUT (device under test). Re-calibration using standardized device cannot be used to check whether the DUT is electrically damaged.
What’s more, damage to precision test equipment is a very punitive in that you cannot do any testing while the equipment is damaged and fixing the damaged (or buying new) equipment is very expensive investment. Therefore, it is imperative to prevent equipment damage through ESD by any means possible. The use of anti-static devices can prevent ESD damage considerably, so electronic test laboratories require their testers to use them at all times during testing.
PS. If you are wondering what EPA stands for in the image above, it is ESD Protected Area. 😎