Questions And Answers

Materials are either conductors or non-conductors.  Non-conductive materials are also called insulators and have a resistance of over 1 x 10¹¹ ohms.  Dissipative material refers to a range of conductive material; greater than 1 x 10⁴ ohms and less than 10¹¹ ohms which has the ESD control benefit of more slowly removing electrostatic charges to ground.  For ESD control purposes conductive refers to material less than 10⁴ ohms except for an ESD Floor which has a special definition.  Per ESD STM7.1-2001 Definitions: “Conductive Flooring Material: A floor material that has a resistance to ground of less then 1.0 x 10⁶ ohms.”

The minimum recommended technical requirement of ANSI/ESD S20.20 for ESD worksurfaces and floors is less than 1 x 10⁹ ohms (see Table 1).  The reason for this is that if a worksurface material resistance is too high (>1.0 X 10⁹ ohms RTT and/or RTG) it will not provide a surface that is sufficiently “conductive” to provide an effective surface to “ground” conductive or dissipative items or materials placed on the surface.

However, typically, we recommend dissipative ESD Mats for worksurfaces, specifically 10⁶ to 10⁸ ohms.  This is in accordance with ESD Association ESD S4.1 and ESD-ADV53.1 Electrical Requirements, "Worksurfaces - Resistance: Between 1 x 10⁶ ohms and 1 x 10⁹ ohms". If the ESD worksurface is too conductive (<1.0 X 10⁶ ohms RTT and/or RTG), it can discharge charged ESDS devices too quickly and possibly cause device damage via the Charged Device Model (CDM).

Typically, we recommend conductive mats for floors; most of the ESD Systems.com Statfree® conductive mats are 10³ to 10⁵ ohms.  Since dirt and other contaminant are typically insulators, the flooring will measure less than 10⁹ ohms throughout the maintenance cycle.

The ESD Association has empirical data demonstrating that if the path-to-ground is less than 3.5 x 10⁷ ohms, the charge on a person will be less than 100 volts.

For Personnel Ground, the minimum recommended technical requirement range of ANSI/ESD S20.20 Table 1 for Flooring – Footwear System is less than < 35 X 10⁶ ohms tested per ESD STM 97.1 Floor Materials and Footwear-Resistance Measurement in Combination with a Person.

This is the resistance in series of the person + ESD Footwear + ESD Floor.  So if the Floor by itself is 3.49 x 10⁷ ohms, it is mathematically impossible to pass this test.  Therefore, we recommend ESD floor mats 10³ to 10⁵ ohms.