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ARTICLE: You and Electrostatic Discharge (ESD)
What is ESD? ESD, short for electrostatic discharge, is the rapid discharge of static electricity from one conductor to another of a different potential. An electrostatic discharge can damage integrated circuits found in computer and communications equipment (definition taken from the webopedia computer dictionary). In fact, ESD can damage without the culprit knowing it.
Sometimes the term electrical overstress (or EOS) is synonymously used with ESD. EOS is an after-effect of ESD. It manifests as electrical hotspots visible only with the aid of a microscope or even a burnt area of a die, in a worse case scenario.
How then, is ESD and its awareness affect you? How is it related to electronics and the computer in particular? Read on as this article can brief you with knowledge on ESD, its causes, and how to prevent or avoid this natural occurring phenomenon.
Often times, if not always, this sticker, label or a variant of it is attached on electronics or computer parts and electronic accessories we buy. It is with a good reason why chips, electronics and computer parts sold, especially those with chips exposed, are tagged with these labels.
Most of the people around us are not aware of electrostatic discharge. As previously stated, this is a naturally occurring phenomenon very much like the revolution of the earth around the sun. ESD occurs on the atomic level, so allow me to delve into the realm of atoms very briefly.
An atom is composed of a nucleus of positively charged protons and uncharged neutrons. Freely revolving around them are almost weightless negatively charged electrons (refer to the diagram on the right). The protons and neutrons in an atom do not change, but the electrons can move from one atom to another. It is because of this reason that life exists and so does ESD.
ESD is primarily caused by the build-up of static electricity or static charge. Static electricity is created when electrons move back and forth between atoms. And when two objects that have different electrical potential or charge approach each other closely enough, this charge may pass from one object to the other in a fast electrostatic discharge. While this only lasts a microsecond or less, the peak discharge current can be several amperes and the peak power can be in the kilowatt range!
One cause of static electicity build-up leading to ESD is the triboelectric effect, in which certain materials become electrically charged after coming into contact or rubbing with a different material and then were separated. A very good example of this is combing or brushing your hair. And placing that comb or brush near torn pieces of tissue paper. The tissue paper gets attracted towards the charged comb. Sparks don't fly but electrostatic discharge occurred. Another would be walking on a carpet, then opening the car door. Be warned, carrying out an experiment with the last example could hurt.
ESD could also be induced. This occurs when an electrostatically charged body is simply placed near a conductive, but electrically neutral body. The mere presence of the nearby charged body causes electrical potential to redistribute themselves on the surface of the neutral body. Even though the object is still electrically neutral, regions of excess positive and negative charge develop, and a potentially damaging discharge may occur when one of these charged regions is suddenly grounded or when a nearby oppositely charged body is placed near it. Charged regions on the surfaces of plastic bags can cause ESD damage to nearby sensitive components via electrostatic induction.
Failures caused by ESD can happen in a number of different ways. The failure can exhibit one or more of the following signs: a short or burnout, resistor/metal fusing together a junction leakage, and a resistor-metal interface rupture. The failure via ESD could manifest immediately rendering a device worthless. Worse than this, a component may be partially damaged and weakened. In semiconductor linggo the failed device is referred to as "walking wounded". It may even remain within specification, but fail later when in use by a customer. It has been estimated that more than 80% of damaged devices may be discovered this way.
ESD can cause unseen damage to electronic devices. The chip or electronic part will still appear in mint condition but the insides already exhibit the damage. Check out a few screenshots of compromised devices upon closer inspection of a microscope.
Another shot of ESD..
The human body was originally the most common and damaging source of electrostatic discharge, thus the most common measurement of ESD sensitivity is by Human Body Model (HBM) electrostatic discharge. It is then proper that a person handling sensitive electronic equipment be aware of ESD and its detrimental effects. Since it is a naturally occurring phenomenon, it cannot be stopped but could be avoided or protective measures could be put in place to minimize its effects.
One of the most common practices in moving toward that goal is the use of a grounding material. The role of a grounding material is to release or discharge the potential before it builds to a harmful level. Another purpose would be to accept the discharge rather than it being released to an ESD sensitive device. Without grounding straps or grounding mats, it is recommended to often touch an unpainted part of a grounded metal surface before handling electrostatic sensitive devices.
ESD compliant clothing such as conductive shoes and smocks are worn by personnel in semiconductor and electronic manufacuring plants. Bunny suits are even required for stricter compliance in some assembly plants. Lining work areas with static dissipative material also prevents ESD.
So when the next opportunity to handle static sensitive devices present itself, remember what harm static electricity can do. Precautionary measures taken to prevent a destructive transfer of static will pay off in the end. We hope awareness of ESD will save you from future headaches.