A Computer Builder’s Guide to ESD - How bad is ESD really?
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How is static generated?
Static is most often caused by the contact and separation of two materials. Note that I did not say rubbing. That can cause static, but it is not necessary; the contact and separation is what matters. This is known as triboelectric charging. When the materials separate, electrons may be transferred from one surface to the other, resulting in a potential between the two objects. Because one of the objects has a buildup of electrons, it carries a net negative charge. Conversely, the other object carries a net positive charge due to an equal lack of electrons. Both objects are charged.
Other ways to build up a static charge on an object are through induction, ion bombardment, and contact with another charged object.
The amount of charge generated is dependant upon many factors: relative humidity, area of contact, and speed of separation to mention a few. The lower the humidity, the more charge is likely to be generated, which is why it is so easy to "zap" yourself on a doorknob in winter, when the air indoors is dried by the heating system.
So, how bad is ESD, really?As I said earlier, an ESD event on an electronic component can damage it or cause catastrophic failure. Some hard drive components are sensitive to potentials as low as 10 volts, and Metal Oxide Semiconductors (MOS variations including Complementary MOS or CMOS) are likely to be damaged by potentials as low as 25 volts. Walking across the carpet in a low-humidity room can generate 35,000 volts easily, and a human typically can’t detect a discharge of under 3,000 volts.
MOS technology uses the ability of an electrostatic field to cause things to happen on the other side of an insulator (in this case, the metal oxide), making for a smaller transistor and significantly less power consumption compared to the larger classic transistor technologies. But because of the small size, the layer of metal oxide glass is very susceptible to damage from higher than normal voltage levels, causing it to crack and allow current to flow through.
Obviously, catastrophic damage is easy to spot. The component doesn’t work. Degradation of a component is tougher to detect. If one has access to a high-powered microscope, then the damage can be seen: bridged conductors, vaporized sections, rough edges, etc. Otherwise it can be difficult to identify. Your component may work perfectly… until it begins to get hot; or it will develop intermittent failures or not work in a certain mode. The useful life of the part will be significantly reduced, to be sure.
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