Two Causes of ESD
Static
electricity is One of the causes of ESD events. Static electricity is
often generated through tribocharging, the separation of electric charges that
occurs when two materials are brought into contact and then separated. Examples
of tribocharging include walking on a rug, rubbing a plastic comb against dry
hair, rubbing a balloon against a sweater, ascending from a fabric car seat, or
removing some types of plastic packaging. In all these cases, the friction
between two materials results in tribocharging, thus creating a difference of
electrical potential that can lead to an ESD event.
Another cause of ESD damage is through electrostatic
induction. This
occurs when an electrically charged object is placed near a conductive object
isolated from ground. The presence of the charged object creates an
electrostatic field that causes electrical charges on the surface of the other
object to redistribute. Even though the net electrostatic charge of the object
has not changed, it now has regions of excess positive and negative charges. An
ESD event may occur when the object comes into contact with a conductive path.
For example, charged regions on the surfaces of Styrofoam cups or bags can
induce potential on nearby ESD sensitive components via electrostatic induction
and an ESD event may occur if the component is touched with a metallic tool.