Can an ESD mat be tested without special tools?

I suspect some meters which cam measure in the tens of megohms can probably produce a reading on some carbon impregnated rubber mats. Then again there are other with a lot higher resistance rubber - I've never tried but perhaps an insulation resistance tester would be able to test those?

Otherwise maybe a DC supply of several volts with the multimeter in series attempting to measure a low current range flowing through probes touched to sections of the mat might also work ...

- Gough

I've tried it with the two kinds of mat I have. This is with 10V from a bench PSU and my 5.5 digit Fluke meter (I also put a 100 ohm resistor in series, in case I touched the probes together, though I  realised after that I could have just used the current limit on the PSU).

Cheap, black, rubbery mat.

a reading over a distance of 10mm of around 8uA

Old, blue, 'Farnell' branded mat

maybe something like 3nA (this is right down near the limits of what this particular meter will read)

Neither is really a resistance. There isn't too much variation with distance.

On a cheap handheld meter, the black one reads about half a megaohm. The probes are more pointed and dig into the surface a bit which is probably why it's less than the 10V/8u reading would suggest (1.25M).

The professional blue one is over-range.

The 3nA figure for the Farnell mat sort of suggests a rough equivalent resistance of 3.33  G ohms but it could be quite a bit different to that (the meter reads 2nA with the probes in mid air and the reading goes up to 5nA on the mat, so I'm not all that confident in it).

Edited because somehow I stupidly wrote Tera rather than Giga.

Hi James,

I just tested a couple of mats here, with a multimeter set to ohms, and the probes about 1 inch apart (near center of mat).

The first mat was plastic-y, not rubbery. It measures around 12k ohm, although the resistance varies depending on the pressure I use. It's 12k with normal probe troubleshooting force.

I don't actually use this mat for soldering or as a work-surface - I chopped it up and used it to line some drawers.

The second mat is some 2-layer material, softer, and has a light-brown side and a black side (the light-brown side is the top surface). The black side has a resistance of about 10 Mohm and again that varies with probe force (more than order of magnitude reduction if pressed more firmly). However the light-brown side I cannot measure this way (I could apply an insulation tester to it, but have not done that yet), so it's at least 50M ohm, the limit of the multimeter, no matter how hard I press.

Nether mat was expensive, the first one was maybe £25/$30 USD, the second is about $50, and both were larger than my desk (maybe 1500mm long, I have not measured).

Very interesting readings - thanks for sharing. If I had a mat, I'd go and measure it too ...

- Gough

It might be interesting to measure the performance of various anti-static bags. The readings I get are all over the map.

ANSI / ESD S4.1-2006

Test Procedure According to ANSI / ESD S20.20-2014, an acceptable work surface will have a point to point and a point to groundable point resistance of less than 1.0 x 10^9 ohms. ANSI / ESD S 4.1-2006 provides test procedures for evaluating the electrical resistance of work surface materials. ANSI / ESD S20.20-2014 defines the control limits for work surfaces that are to be used in an ESD control program where ESD sensitive devices are handled.

Found this online.

https://www.elimstat.com/wp-content/uploads/2019/02/5300-Series-S4.1-Test-Data.pdf

http://documents.desco.com/pdf/TDtypeB2.pdf

Scott

Hi Scott,

Interesting information! I just tried measuring the top surface of my mat with an insulation tester, and now see that it is conductive slightly. I see about 3G ohm with typical probe pressure as if using multimeter test leads. It's in very good condition (unscratched etc, and just a couple of years old), I guess the standard measures it in a different way.

Just out of interest I attempted a lab coat as well, given that it is supposed to be for ESD-safe environment. I think I can just about see some difference in the weaving, but I could be imagining it - I think I see faint rows of single strand of maybe conductiveness, about 5mm apart (horizontal strands in the photo below, about six of them across the photo). But I cannot measure the resistance no matter how hard I try with the positioning of the multimeter leads - also tried the insulation tester. The strands are so fine, I can't get contact with them.. I suppose I could soak two sections of the lab coat and place the probes there! Regarding strands, I don't think the entire surface needs to be conductive anyway. As I understand lots of static discharging can be (say) having a conductive brush very close to a surface. At least it works in my limited experiments.. if I wipe some plastic against some cloth to put on a charge, I can pick up tissue-paper fragments. But if I move a conductive brush close to the surface of the plastic (i.e. close but not touching the surface, and the brush is grounded via me), then the plastic is no longer charged and it cannot pick up bits of tissue paper.

I wonder if the contact point was not a probe but more like a 10x10cm sheet of copper or something similar, whether the parallel paths would reduce the resistance to the levels expected.

Then again, I suppose generating static is a way to test it ... perhaps we need a cat involved ...

- Gough

Gough Lui and shabaz , you both mentioned insulation resistance testers. I haven't used one of those before. Are they just high voltage multimeters?

I'm trying to understand how they work. Seems like happly 1,000 volts to a DUT to measure its resistance would be a relatively dangerous measurement.

Insulation resistance testers are designed to measure leakage currents across insulation. They apply a current limited high voltage DC to measure high resistances (e.g. the Keysight U1461A I RoadTested can measure up to 260Gohm). They can also continually apply this voltage for a set amount of time to do dielectric absorbance tests, etc.

The authority on this, no doubt, is three-phase as he's been reviewing quite a few units in his line of work.

- Gough