ESD is the sudden and momentary electric current that flows between two objects at different electrical potentials.
ESD immunity is a category of electromagnetic compatibility (EMC). EMC is the branch of electrical sciences that studies the unintentional generation, propagation, and reception of electromagnetic energy with reference to its unwanted effects.
EMC describes the ability of a piece of equipment or a system to function satisfactorily in its electromagnetic environment without introducing intolerable electromagnetic disturbances to anything in that environment.
Causes of ESD
One of the causes of ESD events is static electricity, often generated through the separation of electric charges when two materials are brought into contact and then separated (for example, rubbing a plastic comb against dry hair or removing some types of plastic packaging). In these cases, the friction between the two materials creates a difference of electrical potential that can lead to an ESD stress.
Another cause of ESD is 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 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 with excess positive and negative charges.
An ESD stress can occur when the object comes into contact with a conductive path. For example, charged regions on the surfaces of styrofoam cups or plastic bags can induce potential on nearby ESD sensitive components via electrostatic induction, and an ESD stress may occur if the component is touched with a metallic tool.