Author Topic: Testing / maintaining surplus desktop ESD mats for general DIY?  (Read 1060 times)

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Offline evb149

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Hi,

I wanted to expand my ESD safe(r) work areas and I ended up buying some surplus ESD mat material along some some accessories and a couple of even lower grade cheap imported hobbyist type ESD mini mats.

For anything critical I use something new and properly guaranteed and set up but for general handling of less critical things I pinched pennies and went for surplus / imported generic hobby stuff for a couple of areas for now.

Anyway I'm wondering what are the criteria that people use to test out random ESD work area mats in DIY types of scenarios and what can be done to see if mat material is still useful.

Obviously if it was supposed to have a certain level of surface resistance per square due to a coating and/or a certain level of bulk resistivity then it could just be measured in a few spots to see if it is properly conductive.  But I don't know what the original design (bulk conductive or surface conductive and at what resistivity) of these items is so it's hard to say "go or no go" based on an unknown performance standard.
Anyway I haven't dragged out the bench meter to the location to test higher ranges of resistance but it is at least over the couple million ohm range over a small distance between my pocket DVM's probes so whatever it is it isn't highly surface conductive though if could be in the multi-M-ohm range or higher.

Also I'm not sure what cleaning / maintenance "do"s and "don't"s apply to these so I'm wondering what is common.
Will pretty much anything survive a wipe down with a wet and maybe dish liquid soap containing solution?  IPA wipe down?

Is it often relevant to apply some additional ESD surface coating to any of these mats to keep their surface conductivity high as they become worn or abraded / cleaned etc. especially if the original conductivity providing design is a surface coating and not a bulk one?

The material I have larger pieces of is solid blue and about 4mm thick and has a closed cell foam layer for its bulk and a laminated on maybe 0.25mm thick layer that looks like some kind of similarly blue shaded PVC / vinyl though I'm sure it is probably something else.

I could probably get / make some proper "are you not grounded properly" and "ESD detected" alarms but for now I don't have those for my DIY area.

Thanks for any tips!
 

Offline mmagin

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Re: Testing / maintaining surplus desktop ESD mats for general DIY?
« Reply #1 on: April 27, 2017, 12:38:41 am »
I usually wipe my ESD mat down with the ACL Staticide spray.  I also clean the floor up in the area with it.  It appears to be basically non-toxic according to the SDS and I've found it's very effective (sprayed down a 'fleece' blanket and the static is all gone.)

The crude way of measuring surface resistivity in ohms per square would be to use a couple square foil electrodes weighted down with two flat (or slightly convex) heavy objects (spaced apart the same distance as one side of the square).  Place this unknown resistance in series with say a 50 volt DC supply and a common 10 Megohm input impedance DMM.  Record the indicated voltage, calculate the unknown resistance based on the understanding that you have formed a voltage divider of the unknown resistance and the 10M of the meter.  You should be able to reasonably discern resistances up in the several Gigaohm range without resorting to dangerously high voltages this way.

The good quality mats have a dissipative surface (I think generally 1Gohm+) (usually a light colored rubber) on the top and a conductive surface (<100K ohm) (usually a black rubber) under it.  Thus you get good conductivity to the grounding point, but less chance of disturbing measurements when in contact with the surface.
 
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Offline evb149

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Re: Testing / maintaining surplus desktop ESD mats for general DIY?
« Reply #2 on: April 27, 2017, 12:59:27 am »
Thank you very much, that is useful information.

I have never really been in the position of having to non-casually test / maintain professional level ESD equipment and wasn't familiar with the particulars of its construction and resistance design.  The staticide spray is also a good idea, I'll get some for this area when I can.

Not seeing a reading on the quick ohms mode test with my meter and ordinary leads had me wondering what resistance to be looking for.  I'll try the sheet resistance measurement method which you suggeted.

There are probably some little FET input op-amp based ground testing / alarm circuits out there, maybe I'll make one when I have a bit of free time.
 


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