Electro Resistivity Spectrum

The Resistivity Spectrum

Materials used in ESD control fall along a spectrum measured in ohms per square: conductive, dissipative, and insulative. Where a material sits on that spectrum determines what role it can safely play in a protected area.

Conductive Materials

Below roughly 10u2074 u03a9/sq. These move charge very quickly and are typically used for shielding u2014 think metal or metallized packaging u2014 where fast, complete charge equalization is the goal.

Dissipative Materials

Roughly 10u2075u201310u00b9u00b9 u03a9/sq. The most common choice for worksurfaces and packaging: charge drains away in a controlled, slower manner rather than all at once, which is safer for handling live components.

Insulative Materials

Above roughly 10u00b9u00b9 u03a9/sq. These resist charge flow almost entirely, which means they can hold a static charge indefinitely u2014 exactly why they shouldn't be used near a protected area.

Choosing the Right Material

Picking the wrong point on the spectrum for a given application u2014 an insulative tote near bare boards, for instance u2014 is one of the more common and avoidable sources of ESD failures on a production line.

Measuring Resistivity

Surface resistance meters are used to verify that worksurfaces, mats, garments, and packaging actually fall within their intended range u2014 specification alone doesn't guarantee performance after wear.