ESD Matting Resistance

[Cerberus]

Hello,

I am setting up a new lab at home (ds1054z, dg1022, dp832) and I thought it fitting to purchase some ESD protection. I purchased 2.2m of the high quality matting from Oritech that Dave purchased. I decided to test the conductive layer on the back and I got nothing, it seems to be more than the 50 Mega ohms than my BM869 can measure. That doesn't sound particularly "conductive" to me. I was expecting something in the K-ohm range.

With an off-cut (I purchased slightly more than I needed) I really went to town with my probes, completely penetrating the matting and still nothing. I called up Oritech and they told me that I would need a surface resistance meter. Not really keen to shell out for that just to test that my ESD matt is actually doing what its mean to. Can anyone confirm that this is normal?

Thanks,
Serb

Edit: Grammar

[coppice]

Its normal. These things are static dissipative, rather than conductive. That doesn't necessarily require a significant resistance, and most of them appear like an open circuit with a meter than can register a gigaohm or more.

[KJDS]

Think of it as a lot of islands of conductors in a sea of insulator. When the voltage rises then, and only then will it start to conduct. A multimeter won't put out enough volts to start the conduction.

[Cerberus]

I was under the impression that the static dissipative layer was the top blue working surface and the bottom layer was a reasonably conductive layer that "leeched" a charge from the top layer.

I have a 400v 3300f capacitor. Im really tempted to charge it up and give the "conductive" layer a test

I swear there is a video where Dave showed the underside was conductive with a multimeter. However, I believe it was with his old ESD mat and not the new stuff that I have.

[deadlylover]

I tried it with a HP34401A, using just the probe tips I get somewhere from 30-80MOhms, but if I use the sides of the probe tip for more contact, it was around 400kOhms IIRC. I was probing a couple of centimetres apart.

The top layer was something like 200-400MOhms when using my R6581 bench meter.

I'm pretty sure I have the same conductive mat, got mine from Mektronics though as Oritech was out of stock when I purchased it.

It could just be the testing voltage/current of the BM869, do you have another meter on hand to try?

[tooki]

For what it's worth, my ESD mat (a Eurostat 32-200-3609) measures as open on the top surface, and as about 6 Kohm across 60cm of the back (interestingly, the resistance drops over time, so I'm assuming there's some capacitive effect going on). If I measure from one corner of the bottom to the metal contact of my wrist strap, I get about 2 Mohm.

Edit: Using a Fluke 87-V.

[Daz]

I just gave my mat a quick test with a multimeter: on the conductive (black) bottom layer, the resistance was about 150K Ohm over a 7" distance between the probes. Like tooki said, it took some time to get down to this reading.

My mat is only two layer, so the bottom layer is conductive. Do you have a 3 layer mat where the middle layer is conductive and the bottom layer is dissipative?

[Cerberus]

Interesting, I think I'll take an off cut into uni tomorrow and test it on one of the meters there. I would try the LCR bridge, but it would probably be difficult to get a decent reading.

The supplier advertises it as a dual layer mat. When cutting it apart I can only identify two layers. The black conductive layer seems to have a very particularised "glitter" like substance in it.

I have a BM257 (I really like the Brymen's) and I get the same result (not particularly surprising).

It's my understanding that it doesn't matter how far apart the probes are, just that they form a "square". I tried it at multiple distances, from a few mm to 1270mm apart (900mm in the x-direction and 900mm in the y-direction) and I get the same result. I also tried laying the probes sideways in an attempt to increase contact area. I pressed lightly, firmly and completely pierced the matting.

[EEVblog]

See here:

[Cerberus]

Hey Dave,
That's the video I was referring to earlier. Shouldn't I also be able to measure a resistance on the conductive layer of my ESD matting?

[deadlylover]

Hmmmm I think the Brymens have a 0.45V and 1.3V open circuit test voltage for the resistance ranges, perhaps it's too low to get a reading on the mat?

How about if you try putting the 869 into nanosiemens mode?

The HP 34401A is around 5-8V depending on the range, and my R6581 is at a whopping 23V.
Dave's Fluke 87 is specced at <7.3V or <4.5V at the 50Mohm/60nS range.

[Cerberus]

Hi deadlylover, I just tested the 869's voltage output for the ohm's and nanosiemens mode with the 257. I got ~0.5 volts and ~1.3v open circuit (used the crest function on the 257 to capture that).

On the 869, I measured between 0.8 and 1ns for the black "conductive" layer. For the blue dissipative layer I measured ~0.5ns.

That would put the conductive layer at >1 Mega ohm, which I don't think is particularly conductive. Is this something to be expected?

[deadlylover]

1 Mega Ohm is certainly more than conductive enough for ESD purposes. There's nothing wrong with the matting at all, I'm just pondering why you can't at least measure the conductive side on Ohms range. 

[KedasProbe]

Hi deadlylover, I just tested the 869's voltage output for the ohm's and nanosiemens mode with the 257. I got ~0.5 volts and ~1.3v open circuit (used the crest function on the 257 to capture that).

On the 869, I measured between 0.8 and 1ns for the black "conductive" layer. For the blue dissipative layer I measured ~0.5ns.

That would put the conductive layer at >1 Mega ohm, which I don't think is particularly conductive. Is this something to be expected?

Just a correction that is Gohm not Mohm, 1nS is ok for the dissipative layer.
But maybe you have a 3 layer mat, then the high conductive layer is in between, makes the mat stronger.

[Cerberus]

Hi,
Apologies for my late reply, Ive been busy with uni work and work work.
Thanks for that KedasProbe, my mistake, I meant Gohm. I dissected part of the mat under a magnifying lens at uni and I couldn't see three layers. I tore up an off-cut from the mat and tested it right at the junction where the conductive layer meets the dissipative later and I still got the same result. I am fairly certain that it is a two layer mat (as advertised).
I'm at a bit of a loss with regards to this matting. I'm sure that there are a tonne of people in straya have this mat. Anybody getting a similar result?

[Daz]

Hi Cerberus, can Oritech email you the specification of the matting? At least then you'll know what the resistance of the conductive layer should be.

I've just found the spec for my dual layer mat and it says the bottom resistance (Rtt) lies between 1K Ohm and 1M Ohm, using test method SJ/T10694-2004. I don't know anything about this test method, but I did measure 150K Ohm with my multimeter.
The spec then goes on to say that the ESD STM-4.1 guideline for Rtt is >1M Ohm... which is strange because they are stating that this matting falls below the guideline value!

Anyway, if you can get the spec sheet for your mat it might help you.