Electrostatic Discharge (ESD) is the rapid discharge of static electricity from one conductor to another of different potential. Triboelectric charge generation is a common cause of ESD. This occurs when two non-conductive objects come into contact and are separated. Electrons are transferred from one surface to the other making one surface positive and one negative. Walking across carpet is a common example of this. The amount of static buildup depends on the materials involved (see the Triboelectric Series Table).

During a normal workday the human body can store between 1000V- 2500V and is capable of storing over 20,000V. Workers in many cases are unaware of this because human touch is only sensitive on ESD levels that exceed 3000V while electronics can be sensitive to as little as 30V. Once generated, these static charges can remain on the surface for hours, even days. Because so many sources of static electricity can be found in the workplace, removing it completely is doubtful, but many steps can be taken to control the threat.

Here are two images showing ESD damage to a C2 MOS capacitor. What appears to be a slight pinhole on the top image shows to be substantial damage to the trace when examined at 4300X. For more information on preventing ESD, contact a local electronics distributor or ESD equipment manufacturer.

Generally damage is classified as either a catastrophic failure or a latent defect.
Catastrophic Failure Once an electronic device is exposed to an ESD event, the devices circuitry (like in the photos above) may be permanently damaged causing the device to fail. Usually this can be detected using a basic performance test.
Latent Defect A device that is exposed to an ESD event may be partially degraded, yet continue to perform its intended function. ESD latent damage may be detectable by its electrical signature but its lifetime behavior is not predictable. One example can be seen below. Latent damage can result in permanent failure under some stress conditions making the device unreliable. Device outputs with latent damage can fail if current is passed through, but is less likely to happen under nominal electrical fields. This depends on the location of the damage. Damaged junctions are more likely to fail than input resisters.

Much more could be discussed about the subject of ESD. Future articles will include the Human Body Model (HBM) and the Charged Device Model (CDM). Proper ESD workstations and to a greater extent, clean rooms will also be covered.