ESD work mat selection guidelines help, please - Page 1
Forum section: electronics / beginners

author: Michael Weston
author_rank: Contributor
timestamp: August 11, 2012, 10:26:17 pm
content: I thoroughly searched the Web for guidelines about selecting an ESD work mat, and there appears to be no authoritative source without a vested interest in selling mats or specification documents. Further, specifications among different brands and models varies widely in both parameter values and what is specified. So, I have some ESD mat questions whose answers I hope will eliminate any confusion and serve as an accurate guide for myself and others.While these questions are mostly directed to Mr. Dave Jones, I also invite the input of others who do not sell ESD related items.Thanks in advance for any help with these questions.For the purpose of this post, the following definitions apply:RTTisResistanceTop toTop, also known as resistance surface to surface.RTGisResistanceTop toGround, also known as resistance surface to ground.Part 1General ESD work mat details:Which is better for the entirety of the assembled mat "sandwich", including the dissipative layer(s) and the conductive layer combined: high electrical resistance or low electrical resistance?Which is better for the dissipative layer: high electrical resistance or low electrical resistance?Which is better for the conductive layer: high electrical resistance or low electrical resistance?Part 2Regarding the entirety of the assembled mat "sandwich", including the dissipative layer(s) and the conductive layer combined:What should be the minimum RTT?What should be the maximum RTT?What should be the minimum RTG?What should be the maximum RTG?Part 3Regarding the mat's dissipative layer(s):What should be the minimum RTT?What should be the maximum RTT?What should be the minimum RTG?What should be the maximum RTG?Part 4Regarding the mat's conductive layer:What should be the minimum RTT?What should be the maximum RTT?What should be the minimum RTG?What should be the maximum RTG?Part 5Charge Decay (5kV to 50V) as secondsAre any of the questions above unimportant?If so, which ones?Specifically for Mr. Dave Jones:I have some questions about the ESD work mat you reference in "EEVblog #168 - How To Set Up An Electronics Lab" at 25:07:Do you depend on this mat for critical work whereveryexpensive items could be damaged?Who makes this mat?What is the model number of this mat?Is this mat still the one we see in your recent videos?

author: robrenz
author_rank: Super Contributor
timestamp: August 12, 2012, 01:06:38 am
content: This does not answer any of your questions but I think its important. Make sure you get a high temp rubber based mat not a vinyl mat.

author: Michael Weston
author_rank: Contributor
timestamp: August 12, 2012, 02:37:05 am
content: Quote from: robrenz on August 12, 2012, 01:06:38 amThank you for that good advice.Even though I already know a rubber mat is better for high temperatures, I'm glad you brought that detail up so others can lean.

author: gregariz
author_rank: Frequent Contributor
timestamp: August 12, 2012, 02:54:01 am
content: Well you've done more research on it than me. I generally leave it to a reputable manufacturer to make sure the resistances are appropriate. I'm not really sure how important ESD is, its been a long time since I've fried a component. It seems everyone's skin is a little different. I have a workmate who is regularly frying stuff. However, I would recommend a thinner mat (1.5 or 2mm), something like 2 layer rubber mats, which is what I use. The reason is that with the thicker (3 and 4mm) 2 and 3 layer spongy mat I find that surface mount components bounce around on it. Otherwise if you are on the hunt for benches you can buy ESD laminate already on them so you don't need mats anymore.

author: Michael Weston
author_rank: Contributor
timestamp: August 12, 2012, 03:46:19 am
content: Quote from: gregariz on August 12, 2012, 02:54:01 amI think it depends at least in part how critical the device is that is being worked on. I don't think ESD protection would be particularly important for a circuit board that blinks lights for a toy, and at the same time I think ESD protection is of paramount importance if one is working on medical life support devices. With life support, even latent failures could cost a person their life.

author: IanB
author_rank: Super Contributor
timestamp: August 12, 2012, 03:47:39 am
content: I think you have mostly picked the wrong questions. From an electrical point of view, all mats from reputable manufacturers/suppliers, when used correctly, will protect against ESD damage as intended.What will make a huge difference are the mechanical properties. Temperature resistance as already pointed out, but also scratch/cut resistance, abrasion resistance, chemical resistance (liquid flux, circuit board cleaner, other solvents), softness/hardness of the work surface, grip/slide resistance, etc.It is the non-electrical properties where you get to make your choices.

author: T4P
author_rank: Super Contributor
timestamp: August 12, 2012, 04:21:35 am
content: Just don't get the cheap ones,it should be 2 layer rubber with the dissipative layer being 10M-1Gohm and the conductive layer 100k-10MBut yeah, i bought 2 $39 600(L)x900mm(W) from Element14 branded "Multicomp" and they all fit most categories,but the most depressing thing is that it's hard to clean and there are imperfections on the mat, not a problem though

author: Michael Weston
author_rank: Contributor
timestamp: August 12, 2012, 04:26:57 am
content: Quote from: IanB on August 12, 2012, 03:47:39 am"Mostly" means I got 1 or more questions correct; so, please point out which were the correct question(s).Quote from: IanB on August 12, 2012, 03:47:39 amHave you never bought a product from a "reputable" manufacturer, later to discover that the item you bought was garbage? I know there are people who have. For example, at one time Hewlett-Packard Company made excellent products that were built like a brick. Since Compaq bough HP, their product quality degraded considerably. I used to be a big fan of HP, and now I won't buy anything from them; probably ever again.What about high quality products from manufacturers who have yet to be recognized as "reputable"? How can you recognize a bargain from a yet to be recognized company if you do not understand what you should be seeking (like RTT and RTG specifications)?

author: Michael Weston
author_rank: Contributor
timestamp: August 12, 2012, 04:32:19 am
content: Quote from: T4P on August 12, 2012, 04:21:35 amWhat do you define as cheap?Quote from: T4P on August 12, 2012, 04:21:35 amThank you for being very specific. Can you suggest some ESD mats that fit these criteria (manufacturer and model number please)?

author: T4P
author_rank: Super Contributor
timestamp: August 12, 2012, 05:03:44 am
content: The ones that are 1 layer ..This should give you a ideahttp://sg.element14.com/jsp/search/productdetail.jsp?SKU=1687904

author: JohnS_AZ
author_rank: Frequent Contributor
timestamp: August 12, 2012, 05:31:16 am
content: Surface resistivity is not all THAT important. What it will tell you is the condition of the mat. Most importantly, if someone has cleaned it with inappropriate cleansers, or it has been contaminated by dirt, insulative oil films or other materials that would harm its effectiveness. Surface resistivity is measured in "Ohms per Square" and special testers and/or fixtures are needed to conduct this test (ie. Concentric Ring Electrode )Resistance top to top tests the performance of the material by measuring the resistance between several widely spaced points on the mat. This shows if the mat has equal conductance across it's surface. RTT needs to be greater than 10^6 ohms, but lower than 10^12 ohms.Resistance top to ground is the most important test. This measurement is taken from several points on the mats surface to the snap. This tells you if the mat is actually working. RTG should be greater than 10^6 ohms, but lower than 10^9 ohms.Important note .. NONE of these tests can be done accurately with a DMM. Standards call for an instrument that can apply an open test circuit voltage of at least 100VDC (a megger) and five pound conductive electrodes to make test contact with the surface material.(this is all based on EOS/ESD Standard S4.1, and ASTM-F150)(A good basic article about "Ohms per Square" can be read here:http://www.esdjournal.com/techpapr/ohmmtr/ohm.htm)

author: SeanB
author_rank: Super Contributor
timestamp: August 12, 2012, 06:05:03 am
content: All I did was to clean an offcut of conveyor belting and use it. 2M per square ( measured with insulation tester at 500V over a 20mm square) and around the same top to bottom. Free as well, i ordered a belt for work, and when I went to fetch it I asked and went through the scrap bin to get a lot of offcut strips to use as door protectors ( staff and trolleys..........) and this was a piece from that pile. At 5mm thick it could be overthick, but is perfect for me, solder proof, hard to cut by accident and resilient.

author: JuKu
author_rank: Frequent Contributor
timestamp: August 12, 2012, 06:55:04 am
content: Also, single colour and NOT gray. You don't want the small parts play camouflage on you.

author: T4P
author_rank: Super Contributor
timestamp: August 12, 2012, 07:48:20 am
content: Quote from: JuKu on August 12, 2012, 06:55:04 amCamo? They aren't playing camo on me!Top to Bottom should be some other colour on the top and black on the bottom

author: Michael Weston
author_rank: Contributor
timestamp: August 12, 2012, 07:59:08 am
content: Quote from: JohnS_AZ on August 12, 2012, 05:31:16 amThat was a totally awesome reply!Thank you very, very much for everything you wrote.I suspected inappropriate cleansers and contaminants might degrade the ESD effectiveness of the mat. Thank you very much for confirming my suspicion.Thank you for the very interesting link clarifying the meaning of "Ohms per Square".Quote from: JohnS_AZ on August 12, 2012, 05:31:16 amHow can one test if their new mat is proper, or if their existing mat is performing correctly, without spending a big wad of cash?

author: Michael Weston
author_rank: Contributor
timestamp: August 12, 2012, 08:05:59 am
content: Quote from: T4P on August 12, 2012, 05:03:44 amI read the web page from your link, and it describes the mat as having 2 layers. The PDF specifications linked from the product description page confirms the mat as having 2 layers. Did I miss something?

author: T4P
author_rank: Super Contributor
timestamp: August 12, 2012, 08:07:50 am
content: Split my post up ... the cheap ones refer to the 1 layer mats

author: Michael Weston
author_rank: Contributor
timestamp: August 12, 2012, 08:10:49 am
content: Quote from: JuKu on August 12, 2012, 06:55:04 amI had essentially the same thought. I can easily imagine hunting for a SMD resistor on a grey or black mat, then discovering it is immediately in front of me.

author: Michael Weston
author_rank: Contributor
timestamp: August 12, 2012, 08:23:18 am
content: What should be the specifications for Charge Decay time (5kV to 50V)?

author: JohnS_AZ
author_rank: Frequent Contributor
timestamp: August 12, 2012, 04:29:16 pm
content: Test instruments depends on your situation.If you're talking about mats on a whole bunch of benches in a production environment, you really should have good gear. On the lower end of this range is the 3M analog megger:http://www.all-spec.com/products/TM701NIST.html?gclid=COWLjdO74rECFYIaQgodY08AkwOn this high end is the Prostat :http://prostatcorp.com/Resistance-System-SetThis is the instrument I have. The set cost around $2,000US a number of years ago.If you're in a professional/commercial setting and only have one bench to worry about, you can get away with using something like this:http://www.all-spec.com/products/Test_and_Measurement%7CESD_Test_and_Measurement%7CESD-01/SCC-625.htmlIf you're a hobbiest with little or no budget, it gets tougher. You can TRY using the high-ohms setting on your DMM (or let it auto-range). If it reads anything (less than 10^12 ohms) odds are good your mat is working. If you can come up with a few 1% 1Meg resistors, you could actually test your DMM and see how accurate it is in those ranges.I hesitate to include this since I've never seen one (or evaluated it), but there are some VERY cheap meggers on eBay from HongKong. It could easily be a box of shit, but I really don't know:http://www.ebay.com/itm/VC60B-Digital-Insulation-Tester-Megger-MegOhm-Meter-/251078809099?pt=LH_DefaultDomain_0&hash=item3a7576960b#ht_7652wt_1190Also, about decay time ... a decent rule of thumb is that a charge should take MORE than 1 second to dissipate, and less than 10 seconds.

author: Michael Weston
author_rank: Contributor
timestamp: August 13, 2012, 03:43:04 am
content: Quote from: JohnS_AZ on August 12, 2012, 04:29:16 pmThank youvery, very much for another excellent post.I discovered I can get a continuous ESD monitor for about the same cost as a Megger (insulation tester). If you were working on a critical medical device, and you could get only one a continuous ESD monitor,ora megger, and not both, which would you choose and why?

author: Joshua
author_rank: Regular Contributor
timestamp: August 13, 2012, 04:24:04 am
content: When you end up buying one, look at allspec.com They seem to have the best prices on rubber mats I've seen. I've got one and have been happy with it. No affiliation, just a happy customer.

author: Michael Weston
author_rank: Contributor
timestamp: August 13, 2012, 05:31:02 am
content: Quote from: Joshua on August 13, 2012, 04:24:04 amThank you for the tip.I noticed they also have some ESD contant monitors. I need to get some soldering iron tips from All-Spec, so buying the mat and constant monitor from them would be convenient.Which mat did you buy?I read that shipping ESD mats is quite expensive. So, I am curious about the shipping cost. If you are in the USA, how much did the shipping cost and what state were the mats shipped to?

author: SteveyG
author_rank: Unknown
timestamp: August 13, 2012, 10:20:08 am
content: I use these on my benches at home:http://uk.farnell.com/vermason/228116/bench-mat-blue-1-2x0-6m-4x10mm/dp/1833415Seem to be pretty tough, tests out OK using the test instrument I borrowed from work. I also have one of those active monitors which attach to the mat for real time monitoring.

author: tramjoe
author_rank: Regular Contributor
timestamp: August 13, 2012, 11:35:03 am
content: Quote from: Joshua on August 13, 2012, 04:24:04 amI just took a look at them, wow, they are darn expensive IMHO, how is that cheap ? First price is like $70 or more, even for multi-layer vinyl mats ? I mean, for high end rubber mats, this is about the market price, nothing special there (still think this is expensive, but these things seen to be overpriced everywhere), but you can find vinyl mats around for like half that price.

author: T4P
author_rank: Super Contributor
timestamp: August 13, 2012, 01:38:01 pm
content: Vinyl is rubbish ... Accept only rubber

author: robrenz
author_rank: Super Contributor
timestamp: August 13, 2012, 01:52:06 pm
content: These are the cheapest I found that were apparently good quality. I have had mine for over a year and it works great. Resistance values were good when checked with my 8846A and I have not killed anything working on it yet.http://www.ebay.com/itm/2-LAYER-RUBBER-ESD-MAT-24-X-72-W-GROUND-CABLE-/280799452007?_trksid=p4340.m444&_trkparms=algo%3DUPI.GIROS%252BPI.WATCH%252BCRX%26its%3DI%252BC%252BS%26itu%3DUCI%252BUCC%252BSI%252BUA%252BLM%252BLA%26otn%3D15%26pmod%3D280691842577%26po%3D%26ps%3D63%26clkid%3D1298097222268811790

author: nanofrog
author_rank: Super Contributor
timestamp: August 13, 2012, 06:35:19 pm
content: Quote from: robrenz on August 13, 2012, 01:52:06 pmI looked at buying from that seller at one point, but the shipping cost from Canada killed the value for me unfortunately. Sad, as he/she was quite a nice and prompt person to deal with, based on email communications.

author: tramjoe
author_rank: Regular Contributor
timestamp: August 13, 2012, 08:13:23 pm
content: Quote from: T4P on August 13, 2012, 01:38:01 pmI second this. Vinyl melts even with small solder splashes, and if you lose a hair on it, it will scar :-)

author: eevblogfan
author_rank: Frequent Contributor
timestamp: August 14, 2012, 07:13:30 pm
content: helloI am sorry is that's the wrong place to post that .I've seen that's ebay action :http://www.ebay.ca/itm/ws/eBayISAPI.dll?ViewItem&item=270925110123&ssPageName=ADME:X:RTQ:CA:1123is that the right metirial ? ( ie , the same as dave ? )it's 600F resist (for 10 sec) so I guess it will do . but is it "cut proof" ?thank you in advance !

author: T4P
author_rank: Super Contributor
timestamp: August 14, 2012, 07:28:30 pm
content: From the picture? I'll say no. It's got these ridges on the surface that's totally unlike

author: eevblogfan
author_rank: Frequent Contributor
timestamp: August 14, 2012, 07:39:13 pm
content: heythank you ,I'll ask him for pics ,but what exactly the ridges tells you about the mat ?

author: nanofrog
author_rank: Super Contributor
timestamp: August 14, 2012, 10:08:02 pm
content: robrenzhas a mat from that eBay seller (posted on the previous page), and said it's worked well for the year+ he's had it.So if it's the right price vs. other sources for you, I'd say go for it.

author: eevblogfan
author_rank: Frequent Contributor
timestamp: August 14, 2012, 11:25:59 pm
content: hey thank yousorry I red the whole 3 pages now ,well , the shipping price is a BUMER , a real one .but I think I will put it on my watch list ,another Question : is it like daves (Ie cimical resist and "cut proof" ) ?

author: JohnS_AZ
author_rank: Frequent Contributor
timestamp: August 15, 2012, 03:17:21 am
content: Quote from: Michael Weston on August 13, 2012, 03:43:04 amSorry for the delay. Went to the oral surgeon and have been knocked out a couple days.If you can only get a megger OR a constant monitor, I'd buy the constant monitor. A constant monitor actually functions as a crude form of megger. It doesn't make as accurate a measurement, but it does ensure there is an electrical path to ground, and it does it 24/7.

author: Michael Weston
author_rank: Contributor
timestamp: August 15, 2012, 05:12:59 am
content: Quote from: JohnS_AZ on August 15, 2012, 03:17:21 amThank youagain for yet another excellent post!I suspected the constant monitor might function like a megger to some degree. Thank you very much for that confirmation!Quote from: JohnS_AZ on August 15, 2012, 03:17:21 amIt is totally OK (the delay).My sympathies to you for your oral surgery. When I went to the oral surgeon, I was out for days too. I hope you feel much better very soon.

author: Michael Weston
author_rank: Contributor
timestamp: August 15, 2012, 05:31:41 am
content: Quote from: SteveyG on August 13, 2012, 10:20:08 amThanks for the tip.I checked the Farnell web page in your link, and I was a bit surprised the data sheet link there was not for your mat.I also noticed that specification sheet did not state the Charge Decay time. So, I hunted down the correct specification sheet for your mat, and it also did not state the Charge Decay time. That bothers me. I'm betting if they don't put the charge decay data in the specification sheet, they don't know the duration, and if they don't know the charge decay duration, they did not test the mat fully and correctly. The charge decay data omission somewhat says to me they might not be the best choice. I hope for your sake, the omission of the charge decay data in the specification sheet was just a mistake, and the mat truly is proper anyway.I'm happy the mat is working out well for you, and I hope your circuits do not have or get any latent failures.What sort of devices do you work on using this mat?