When customers look at the technical datasheet (TDS) for LINQSTAT Volume Conductive Film, they often are confused by the Electrical Properties. The 3M Velostat material lists only Volume Resistivity as less than 500 ohm-cm, yet the LINQSTAT material lists Volume Resistivity, Volume Conductivity and Surface Resistivity. The fact of the matter is that they are all related, and if you know the Volume Resistivity of the material and the thickness of the sheeting, then you can calculate the other values.
Surface Resistance multiplied times the thickness of the material in centimeters, equals the volume resistivity.
Volume Resistivity vs. Volume Conductivity
Volume Resistivity is also called bulk resistivity because it is the inherent resistance of a semiconductive material independent of shape or thickness. Very simply, resistivity is the inverse of conductivity. Volume Resistivity is measured in Ohms-cm, or spoken as “ohms-centimeter” and Volume Conductivity is measured in S/cm, or spoken as “Siemen per centimeter”. Therefore, a Volume Resistivity of 500 ohm-cm is equal to a Volume Conductivity of 1/500 or 0.002 S/cm.
Volume Resistivity vs. Surface (or Sheet) Resistivity
Surface Resistivity (also called Sheet Resistivity) is expressed as Ohms/sq, spoken as “ohms-per-square”. It is a useful measurement when measuring a layer or thin film of a semiconductive material such as LINQSTAT as the surface resistance of a given material will change depending on the thickness of the layer. Surface Resistance (ohms-per-square) multiplied times the thickness of the material in centimeters, equals the volume resistivity (ohms-cm). Likewise, the Volume Resistivity divided by the thickness in centimeters equals the surface resistivity.
Therefore, looking at the LINQSTAT VCF materials, the surface resistivity of each material can be determined based on the thickness of the film and the volume resistivity (<500 ohm-cm)
- VCF-2xxxxS-Series: 500 ohm-cm / 2mil (0.00508cm) = 98,425 ohms/square
- VCF-4xxxxS-Series: 500 ohm-cm / 4mil (0.01016cm) = 49,213 ohms/square
- VCF-8xxxxS-Series: 500 ohm-cm / 8mil (0.02032cm) = 24,606 ohms/square
Why does CAPLINQ give “less than” values (ie. <500 Ohm-cm) instead of Typical Values?
LINQSTAT Volume Conductive Film is a carbon-loaded polyethylene. As such, there are necessarily some differences in the conductivity over the entire surface. The data that CAPLINQ provides is meant to be a minimum, repeatable value that can be used in the design of the final product.
For more information on LINQSTAT VCF-Series, please contact us or visit the CAPLINQ website today to find out more, or for more information.