In controlling ESD, materials with different resistive properties are used. These same materials can be used in automatic assembly equipment to obtain the desired results. The nomenclature used to specify the resistive attribute of the material is usually surface or volume resistivity. A brief explanation of surface resistivity is a value obtained by measuring resistance between two electrodes placed on the same surface. The geometry of the electrodes and the resistance values are combined through calculations to obtain ohms per square.
Meters are available and calibrated to display ohm per square.
Volume Resistivity Volume resistivity is the resistance of a material through its thickness. The units of measure is ohms centimeter or ohms inch. Conductive Materials Conductive materials are materials with surface or volume resistivity less than 106 ohms per square or ohms centimeter, respectively. Either a substance is added to the material during the manufacturing process or it is topically applied. Antistatic materials do not necessarily correlate to surface or volume resistance.