June 7, 2020 component testing

Measuring stuff with the Vermason Surface Resistivity Tester

A comparison of the sheet resistance of different materials

Measuring stuff with the Vermason Surface Resistivity Tester

I am measuring the surface (or sheet) resistivity of various materials that are commonly used to handle electronics. The instrument's accuracy is 10%. The last time it was calibrated was in 1999. More than 20 years ago. This is by no means an exact measurement. Rather a comparison of materials.

Methodological problems

I made all measurements with the concentric probe shown in the photo above. According to the manual, when the concentric probe is used the results should be multiplied by a factor of 10. To verify this I measured two different materials using the following methods:
1. Concentric Probe
2. Two probes 10cm apart
3. Two probes 20cm apart
4. Two probes sandwich configuration (see photo)
5. Square probe (on the device) weighted with a probe (2.5kg)
No mater what I tried the results were the same. I am a bit confused with the correction factor...

ESD foam sandwiched between the probes

Finally the results

So I present the results without correcting for the concentric probe. The numbers are normalized to GΩ□ (gigaohms squared) for easier comparison.

Good >0.001GΩ□ <10GΩ□

  • My ESD Matt < 1 GΩ□
  • ESD Foam <0.035GΩ□
  • Cheap Chinese ESD Matt <10GΩ□
  • Digikey metallized bag inside <1GΩ□ outside <10GΩ□
  • Digikey blue dissipative bag <10GΩ□
  • Cutting mat ebay < 10GΩ□
  • Printer Paper < 1GΩ□
  • Wood (pine unvarnished) < 1GΩ□

Marginally good >10GΩ□ <100GΩ□

Marginally bad >100GΩ□ <1000GΩ□

The resistivity of some materials like parer depends also on humidity. The environmental conditions at the time of measurements were 21°C, 50%RH, elevation 625 m.