ESD / EOS Brushes

An ESD/EOS brush can be an active or a passive static eliminator.

Active Conduction

The active ESD/EOS brush works because, in the process of mechanically brushing the potentially charged surface, the conductive brush fibers and a conductive or static dissipative core allow the static charge to flow to ground through conduction. Conduction is the transfer of a charge through direct contact.

Passive-Induction

An ESD/EOS brush can also be constructed as a passive static eliminator with an air gap between the fiber ends and the charged surface. Induction is the process by which a chargeís field establishes a charge in a nearby conductive object without physical contact. A charged surface has an electric field emanating from it. In most situations, the electric field will be uniform and perpendicular to the surface. However, if a sharp point is brought into the vicinity of the field, the field lines will concentrate at the point. In situations where the point is sufficiently sharp, the value of the electric field gradient at the point tip will be greater than the breakdown strength of air [3,000 volts per millimeter]. This, the corona effect, causes the air molecules in the vicinity of the point tip to ionize. Since the ions are also subjected to the electric field, ions of one polarity [opposite the charge polarity of the surface] will travel along the electric field lines to the surface. This will reduce the static charge on the surface. The opposite polarity ions will travel through the passive device to ground. This process will continue until the field has been reduced to the point where ionization stops [around 2,000 volts].

Location of the passive device is critical in affecting the degree of electrostatic dissipation on the substrate. The devices should be located where there will be free air space directly opposite the ends of the conductive fiber and the charged surface. By allowing free air space, voltage suppression will be avoided. Passive devices should also be placed beyond the last point of frictional contact to prevent further charges being generated.