The Triboelectric Effect
What we normally call static is more properly known as contact electrification caused by the triboelectric effect. Ungrounded materials can become electrically charged when they contact another material and then become separated. While in contact, or “adhered,” electrochemical charges move between the two objects, and when separated, there can be an imbalance of electrons between them, with one object having more and the other having less. Once the surface of an object is charged, coming into contact with a non-charged object can cause a sudden discharge of the static. Essentially, it’s a tiny lightning bolt. If you’ve ever noticed that you can get shocked when climbing out of your car after a drive, it’s because the car’s metal shell has built up a charge from rubbing with the passing air. (Air can act as an electrically charged material, too.) No doubt, you’ve noticed that static tends to be more prevalent in the winter when air is dry. This is because moisture in the air helps electrons to dissipate more quickly so less static charge can build up.
There are three kinds of component failures caused by ESD: catastrophic, latent, and upset. As you might expect, catastrophic failure means your device is toast. The damage done to the component is extensive enough that the device is rendered permanently inoperable. Latent damage is considerable but, like that nail to the head, may not result in system failure for a long time to come. Upset damage will typically cause intermittent problems, making troubleshooting difficult.
According to an ESD training presentation I obtained from Tektronix, only 10% of ESD-caused failures are catastrophic. The vast majority are latent and upset failures, leaving the device operational but unpredictable.