Anti-static mat testing

[RJFreeman]

I was asked about testing Static dissipative workbenches, and figuring testing wouldn't be the hardest task on earth, I purchased a surface conductivity tester off eBay for about $35.
when it arrived I wanted to check it worked, so I tested the Anti-static mat I got from Jaycar last year.

To be brief, the mat failed (I will add pictures below), my tester classified it as Insulative, results did vary depending on where I placed the tester on the mat, and whether I pushed down on the tester or not (although my understanding of the test procedure suggests the tester should just sit on the surface

So I dug out an old Patlon ESD mat (this is the Dark blue one in the pictures) I have had for years, and the tester consistently gives this a reading of 10^9 (which it says is OK) no matter where I put it on the mat, and without pushing it down.

I also tested:
A bag from Digikey (the one with capacitors in it) which gave me either 10^10 and 10^11, but did this consistently.
A static shielding bag which gave me at 10^10, no matter where I tested it.
and a cardboard box which gave me 10^9, and again moving the tester around did not change this reading.

So disturbingly, while the surface resitivity tester is new, and therefore could be suspect, the Jaycar Anti-static mat appears to be the odd one out. I even gave the Jaycar mat a wipe down with a damp cloth, and dried it in the sun, but still get similar results.
Might be time to dig out the megger, to act as an adjudicator....

[julianhigginson]

I reckon you've done more testing than Jaycar...
And I'm not surprised at the results.

[RJFreeman]

I reckon you've done more testing than Jaycar...
And I'm not surprised at the results.

Ironically the Tester cost less than the Mat, so they can hardly claim it cost too much to test them.....

Although I suspect everyone just buys them just expecting them to work as described (as did I to be honest)

[Gregg]

About 25 years ago I was working for a large telecom company that had anti-static mats on the floors even though the raised floor was very well grounded and used anti-static tiles.  The facilities person and I found some new testers for the mats and were playing around with them to see if we could use them for megohm meters on other devices.  If I remember, they were battery powered and output max of about 24 volts.  To make contact with the mats they came with two weights about 5KG each and about 80mm in diameter with what looked like a smooth tin plated surface on the bottom each with a wire to the handheld meter.  The instructions were to wash dirt off the mat where the contacts were to be placed (I forget the distance recommended) and the meter was analog with only good / bad indications.  They were not terribly useful for anything else so they were put back under the raised floor with the rest of the junk that was not supposed to be stored there. 
After seeing commercial anti-static test equipment, I thought that some aluminum foil and a standard megohm meter would probably give as good or better indication of the real properties of anti-static mats.

[bitseeker]

Interesting. Does this mean I need to buy a surface resistance/conductivity tester or are there alternative testing methods that are qualitatively effective even if not as quantitative?

[RJFreeman]

I am still trying to work out what the test standards require (not the least because you need to have paid up membership of the ESD Association to access the standards, or pay up $145 USD per document, and well, I am not that flush with cash) the main standard referred to reference S4.1 which is $135 to download.

ANSI/ESD S20.20-2014 requires 1X10^9 ? or better from a work station surface to ground so cardboard, and the Patlon mat are fine according to the tester.

I did manage to get hold of a copy of ESD TR53-01-06 (Compliance Verification of ESD Protective Equipment and Materials) however, which describes tests using the following:

An integrated checker or meter, whether it is a single meter or a collection of instruments that are capable of measuring at least 1.0 x 10^10 ? with a test voltage of 10 and 100 volts (± 10%) DC open circuit.

Test electrodes are Cylindrical 2.27 ± 0.06 kg (5 lb ± 2 oz) with a diameter of 63.5 ± 0.25 mm (2.5 ± 0.1 inches) having a contact of electrically conductive material with a Shore-A (IRHD) durometer hardness between 50 and 70.
The resistance between two electrodes should be less than 1.0 x 10^3 ? when measured at 10 volts on a metal surface.

my (low cost) tester does not follow TR53 (the lack of 5lb electrodes gives that away), although other (more expensive) testers are similar to mine.
I can't find any standard that describes this test, but the manuals for the other testers often say something along the lines of:
"The Surface Resistivity Tester has not been designed to meet ANSI EOS/ESD-S4.1 test equipment requirements.
This test instrument is intended for use only as an auxiliary tool for monitoring surface resistivity performance."

So I guess Technically I can't say the Jaycar mat fails TR53, although the results are strongly indicative.....

[bitseeker]

Is it possible to roughly gauge if a mat is OK using, for example, an electrometer with probes placed X mm apart on the surface?

I suppose a poor-man's version of a test could be something like the following:

1. Rub your socks on carpet for X seconds and touch a grounded metal surface to confirm successful static charge buildup.
2. Rub your socks on carpet for X seconds again and place hand on static dissipative mat for Y seconds, then touch grounded metal surface to check for significant residual charge. Nothing = mat may be functional. Zap = mat not functional or repeat with greater Y.
3. Rub your socks for X seconds on carpet again, place hand on static dissipative mat for Y seconds, then touch static-sensitive electronic component. Component working = mat may be functional. Component dead = mat not functional or repeat with greater Y (and new component).

[tpowell1830]

Back in the '90s I worked for a pacemaker company and all assembly areas, including all the test areas had to have anti-static mats. We purchased the anti-static mats which were about 6mm thick and about 60cm X 40cm. We were governed by the FDA and a few other US government bureaus and were required to setup regular maintenance to check that the mats were performing as per mfg specifications. 3m provided guidelines for setting up these mats, and we mostly followed their guidelines.

The mat material that we purchased came in rolls made by the 3M company, so we cut them to the sizes described above, and we purchased the button down connections and installed them on 3 corners of the mats and connected a wire with an inline 1Mohm resistor to one corner of the mat to ground. The buttons had sharp sheet metal prongs that we would force through the mat and bend over the prongs. All of the wrist straps that were purchased had a 1 Mohm resistor in the lead as well. When workers came to this work area, they were required to snap on to one of the buttons with their wrist strap. The tester was purchased and was similar to the ones described above, a very heavy metal contact device and a go/nogo meter connected to it. One lead of the meter was connected to ground and the other was connected to the heavy contact device. I don't remember the make or model of the test device.

The technicians would check all of the mats in their area once a month. We rarely had failures for these mats, but often they would get very dirty and get replaced with new ones.

If not helpful, I hope you found this interesting.

[ajm1540]

I am shopping for an affordable quality working anti-static mat for a new bench I am setting up.  I ran across a post from 2010 (linked below) where someone (slowly) discharged a capacitor through the mat do determine the mat resistance.  I am finding the lower-cost mats make no mention of ANSI/ESD S20.20.  I also saw a Sierra brand mat listed as meeting ANSI/ESD S541-2003 which is a standard for anti-static packaging (bags).

https://www.mail-archive.com/elecraft%40mailman.qth.net/msg94407.html