How important are ESD mats?

[Trinity]

I have a basic question about ESD mats - specifically, how important are they?

Assuming you're working with a proper wrist strap on a standard workbench surface (i.e. finished wood), how important is it to use an ESD mat?  I would think that because you're grounded through the strap, you're going to be dissipating charge on the working surface as you regularly come in contact with it.

Are the benefits of a grounded mat significant, or does it just add a small amount of convenience and protection?

[Rick Law]

I have a basic question about ESD mats - specifically, how important are they?

Assuming you're working with a proper wrist strap on a standard workbench surface (i.e. finished wood), how important is it to use an ESD mat?  I would think that because you're grounded through the strap, you're going to be dissipating charge on the working surface as you regularly come in contact with it.

Are the benefits of a grounded mat significant, or does it just add a small amount of convenience and protection?

You have no flag indicator, so you did not select where you are from (like me).

I am no EE expert, but I have some experience to share.  It is where you are that is as important as what you are doing.

Where I was as a kid, I did not see static electricity discharge - until I was almost 20 years old  after a long distance move to a different part of the world.

In some parts of the world, the humidity is at a level that static discharge is hardly an issue for the last few million years.  Some parts of the world, you walk, you get shocked every time you touch metal...

(Just throwing monkey wrench around..)

But seriously, whatever answer you get likely is not an answer applicable world-wide.  You probably should say something about average level/frequency of ESD you encountered so other experienced EE guy can give you an applicable answer.

Rick

[nctnico]

IMHO it is always important to use an anti-static mat. Even if it is just a large anti-static shielding bag.
I have seen failures which could be correlated with not using any anti-ESD measures during assembling computers. A vailuable lesson! When I test/handle products for customers I always use an ESD mat to put the products on and wrist strap to discharge myself.

[Trinity]

IMHO it is always important to use an anti-static mat. Even if it is just a large anti-static shielding bag.
I have seen failures which could be correlated with not using any anti-ESD measures during assembling computers. A vailuable lesson! When I test/handle products for customers I always use an ESD mat to put the products on and wrist strap to discharge myself.

Compared to not using anything at all, I agree with you 100%.  However, the question here is how much benefit there is to a mat when you're already using a wrist strap.

[Trinity]

In some parts of the world, the humidity is at a level that static discharge is hardly an issue for the last few million years.  Some parts of the world, you walk, you get shocked every time you touch metal...

Generally speaking, you're absolutely correct.  And that would have a direct effect when not using any ESD measures at all.  However, if you're already using a strap, you're going to be dissipating any charge that accumulates in your body.

I know that ESD smocks are used to protect against charge build-up for people wearing clothing made from synthetic fibers.  I'm just curious what benefit there is to using a mat if you already have a grounding strap on.

[DanielS]

The main benefit to having a mat and grounding yourself to it is that you no longer need to worry about you and your work items being at the same electrostatic voltage since the connection between you and the mat all your stuff is on guarantees it.

You can make-do without a mat or wrist strap altogether but then you have to be mindful of how you grab stuff, the surfaces you leave stuff on, how dry the air is, etc. to avoid touching stuff at a time where there may be a significant electrostatic charge difference.

With the strap and mat, you can forget about all of that and focus on your job instead of worrying about ESD every time you are about to touch something.

The strap and mat makes ESD protection almost idiot-proof.

[Trinity]

You can make-do without a mat or wrist strap altogether but then you have to be mindful of how you grab stuff, the surfaces you leave stuff on, how dry the air is, etc. to avoid touching stuff at a time where there may be a significant electrostatic charge difference.

With the strap and mat, you can forget about all of that and focus on your job instead of worrying about ESD every time you are about to touch something.

The strap and mat makes ESD protection almost idiot-proof.

Yes, but like the other posts here, you're comparing having both with having neither.  The question is how does having a mat compare with not having a mat when you're using a wrist strap under both conditions.

[coppice]

I have a basic question about ESD mats - specifically, how important are they?

Assuming you're working with a proper wrist strap on a standard workbench surface (i.e. finished wood), how important is it to use an ESD mat?  I would think that because you're grounded through the strap, you're going to be dissipating charge on the working surface as you regularly come in contact with it.

Are the benefits of a grounded mat significant, or does it just add a small amount of convenience and protection?

Do you keep sweeping your static dissipating hands over every corner of your worktop, to ensure it is all discharged? If not, and if the worktop lacks any ability to spread the charge around, there will be charge hot spots where placing equipment could zap it. Actually grounding a static dissipating mat might not be critical if you keep touching the mat with something grounded, like your hand. However, you do need a worktop which will spread the charge around, so it can be drained by that hand.

An ioner over the bench can greatly reduce the need for a mat, as these neutralise charge build up in a distributed manner that will eliminate charge hot spots on the worktop. Moving to the humid tropics, and putting the bench in a sauna can work too.

[VK5RC]

I don't use a wrist strap but with the clothes I typically wear I don't get any shocks,  I do use a esd mat and soldering iron.
Touch wood no problem so far but if in a controlled (commercial production) environment you should.

[luky315]

Full ESD protection is important to distinguish between amateurs and professionals :-)

[larry42]

As others have mentioned, it depends on your environment. Just like how seat-belts are not needed until you crash...

ESD mats are cheap, especially the vinyl ones and should provide a useful level of protection when combined with a wrist strap.

(NB buying multiple square meters of high quality rubber ESD mats does get expensive (!))

[george graves]

I'll also say it depend on your climate...

You'll know if static is a problem.  If you're like me, and the west coast of the US (Santa Barbara, Seattle, or near a beach) - static electricity doesn't exist.

If I'm installing a $1200 i7 chip into a motherboard, yea, I ground myself.  Otherwise, I've never lost a chip to static.  - maybe dave should do a video on how robust chips are. 

[JuKu]

Strap protects everything you touch, but does nothing for stuff touching the table.

[schopi68]

George, you think that you've never lost a chip to static. But this can only be said if you are sure that none of your chips failed in the years after installation. Most static damage does not result into immediate failure of components.

If you could eliminate static charging by just raising the humidity of the environment, this would be one of the easiest solutions in large production environments. Yes, humidity loweres the static charge, but it does not eliminate it.
In this document there are some values listed. www.minicircuits.com/app/AN40-005.pdf

Most chips with input protection are designed to withstand 2kV in accordance to the human body model. But in most cases this protection requires the chip to be already installed to work.

[Trinity]

Do you keep sweeping your static dissipating hands over every corner of your worktop, to ensure it is all discharged? If not, and if the worktop lacks any ability to spread the charge around, there will be charge hot spots where placing equipment could zap it. Actually grounding a static dissipating mat might not be critical if you keep touching the mat with something grounded, like your hand. However, you do need a worktop which will spread the charge around, so it can be drained by that hand.

An ioner over the bench can greatly reduce the need for a mat, as these neutralise charge build up in a distributed manner that will eliminate charge hot spots on the worktop. Moving to the humid tropics, and putting the bench in a sauna can work too.

Fair enough, and good points all around.  I'm curious how quickly hot spots would develop if you start off by sweeping the working surface with your grounded hand.

[Rufus]

Strap protects everything you touch, but does nothing for stuff touching the table.

A strap does not protect what you touch. Touching something that is charged with respect to ground still zaps you and it.

That is why a mat or conductive work surface is more useful than a strap, it is easy you touch the surface and ground yourself before touching anything on it.

Years ago a mechanic wanted to hand an EPROM from an ECU to me, held between thumb and forefinger. I instinctively tried to touch his hand before grasping the EPROM. I got a strange reaction, he thought I was drunk or something and missed the EPROM.

ESD isn't complicated, everything is a capacitor which can be charged, when you form new circuits which might discharge the capacitors make sure it isn't though a point which can be damaged by the resulting voltage and current.

[nanofrog]

Between a mat and a wrist strap, a mat is more critical (wrist strap is an accompaniment to a mat). That said, you really want both.

Plenty of articles out there if you search. 3M and Desco have some good ones IMHO. Granted, they both manufacture ESD related products, so you can take a look at ESD PROTECTION PROGRAM by Linear Technologies as a more non-partial source (chip maker, not ESD products/supplies).

[sotos]

No problem here in Greece Athens.

I repair, maybe 20 years pcb.s , I had or have no problem with esd.

5 years I worked for the greek navy repairing electronic cards for frigates –helicopters.

No problem with esd.    Also other repair facilities don’t have problems with ESD, maybe it’s the climate here.

No mats, no wrist straps.

They keep flying and sailing.

[Trinity]

A strap does not protect what you touch. Touching something that is charged with respect to ground still zaps you and it.

This doesn't seem right.  The strap has a high ohm resistor integrated in it which is designed to control the current flow of discharge.  If you touch something charged with respect to ground, that charge dissipates through the resistor in the wrist strap, which keeps the current to a non-damaging level.

[AG6QR]

A strap does not protect what you touch. Touching something that is charged with respect to ground still zaps you and it.

This doesn't seem right.  The strap has a high ohm resistor integrated in it which is designed to control the current flow of discharge.  If you touch something charged with respect to ground, that charge dissipates through the resistor in the wrist strap, which keeps the current to a non-damaging level.

No, your body has capacitance, as does the chip or board you're handling.  The resistor is only on your wrist strap, so the resistor only limits the current flow through that path.

If you pick up a chip that has a charge on it of a few thousand volts relative to you, as soon as you touch the chip, your voltage and the chip's voltage equalize, and the resistor in the strap doesn't limit the current that flows during this equalization zap.  Now it's true, if the voltage at which you and the chip equalize is significantly different from ground potential, the strap resistor will slowly bring your voltage back to ground.  But that's after the damage was already done.

If you've got an antistatic mat as well as the wrist strap, then the chip laying on the mat is at the same potential as you are, so you'll never pick up a chip at significantly different potential from your own.  If you only have the strap without the mat, then your body will stay at ground potential, but the things on your bench may not.

[Trinity]

No, your body has capacitance, as does the chip or board you're handling.  The resistor is only on your wrist strap, so the resistor only limits the current flow through that path.

If you pick up a chip that has a charge on it of a few thousand volts relative to you, as soon as you touch the chip, your voltage and the chip's voltage equalize, and the resistor in the strap doesn't limit the current that flows during this equalization zap.  Now it's true, if the voltage at which you and the chip equalize is significantly different from ground potential, the strap resistor will slowly bring your voltage back to ground.  But that's after the damage was already done.

If you've got an antistatic mat as well as the wrist strap, then the chip laying on the mat is at the same potential as you are, so you'll never pick up a chip at significantly different potential from your own.  If you only have the strap without the mat, then your body will stay at ground potential, but the things on your bench may not.

That is exactly the information I was looking for, thank you!

Out of curiosity, the human body model for capacitance is 100 pF.  Is that enough to cause the damage we're talking about?

[DanielS]

Strap protects everything you touch, but does nothing for stuff touching the table.

A strap alone does not protect anything you touch: if you are grounded but touch a part on an insulated surface that already has an electrostatic charge other than ground, touching it the wrong way may still kill it.

That's why you should have a grounded dissipative mat to put your parts on if you do not want to worry about how you pick up parts.

With a mat but no strap, you just need to remember to put a hand on the mat before touching anything else on it to safely equalize charge.

[AG6QR]

Out of curiosity, the human body model for capacitance is 100 pF.  Is that enough to cause the damage we're talking about?

Short answer, yes.

Longer answer:  the input capacitance for a CMOS logic gate is approximately 5 pf, or 5% of the capacitance of the human body.  If the chip was stabilized at a static potential of, say, 1 kV with respect to ground, and you touched one pin of it (you always touch one pin before you touch the others), then the 5 pf capacitor dissipating into the 100 pf capacitor of your body is going to bring the voltage of your body only up a little bit, roughly 5% of the original 1 kV.  That means that, after equalization, the input pin is at a potential very close to ground, while the rest of the chip is still at its original 1000V.  In other words, most of the static voltage that was on the chip is now present across the thin dielectric of the input transistor.  Will the dielectric break down under that high voltage?

This is pretty nearly the same as what happens if you had neither a grounding strap nor a static mat, and you picked up a chip that was at near ground potential while you had a static charge on your body (except the sign of the charge may be reversed, a bookkeeping issue only).

OK, it could be that a person walking around has more opportunity to build up a significant static charge than an object laying on the bench.  By that logic, maybe the wrist strap might be a bit more important than the antistatic mat.  But they're both important. 

Another thing to note -- it doesn't make a whole lot of difference whether things are at ground potential or not -- what matters is that they're all at the SAME potential.  So it's more important to see to it that there's a current path between your wrist and the work surface than to see to it that there's a path between your wrist and earth ground.

[Trinity]

OK, it could be that a person walking around has more opportunity to build up a significant static charge than an object laying on the bench.  By that logic, maybe the wrist strap might be a bit more important than the antistatic mat.  But they're both important. 

Thank you for the clarification.

Another thing to note -- it doesn't make a whole lot of difference whether things are at ground potential or not -- what matters is that they're all at the SAME potential.  So it's more important to see to it that there's a current path between your wrist and the work surface than to see to it that there's a path between your wrist and earth ground.

That I understand.  To me, it was the resistance on the path to ground that was the desired factor, not the ground itself.

[zapta]

5 years I worked for the greek navy repairing electronic cards for frigates –helicopters.
No problem with esd.    Also other repair facilities don’t have problems with ESD, maybe it’s the climate here.
No mats, no wrist straps.
They keep flying and sailing.

Hopefully you didn't work on this one ;-)

http://www.cnn.com/2010/WORLD/europe/07/30/greece.helicopter.crash/

Seriously, one of the problems with ESD damage is that it it's not always apparent and can manifest itself down the road.

[george graves]

George, you think that you've never lost a chip to static. But this can only be said if you are sure that none of your chips failed in the years after installation

I can!  But....I see what you're getting at.  I have no proof, other than my "educated guess" - That and of 1000's of *widgets* (automotive timed relay kind of thing - very basic - opamp/RC time/mosfet) that are running 24/7 since 2007,  none have failed other then water intrusion...Visible water damage (floods in the US during storm season)

But I agree it's "good practice" - I just fitted my lab with the same mat Dave uses.  Except - mine is green.  Whoops!  The leaded solder won't know what to do with one's self!

Most static damage does not result into immediate failure of components.

Not sure what to say....Most cheeseburgers don't result in heart attacks!  Do you have any more info on that? Static...not cheeseburgers. 

[shakilabanu]

I have a basic question about ESD mats - specifically, how important are they?

In my experience I've not noticed any difference with or without ESD ... in my earlier workplace there werent any and in my present work place they are used on most of the workbenches, but I havent yet noticed any difference. FYI I am in humid conditions, peninsular India.

[German_EE]

Opinions vary according to circumstances.

If it's a hobby thing then a grounded wrist strap is probably enough.

My last job was working on elevator control circuits where a product failure in a control board could be unfortunate. We therefore used wrist straps, mats AND had anti-static flooring in the workshop.

[schopi68]

Most static damage does not result into immediate failure of components.

Not sure what to say....Most cheeseburgers don't result in heart attacks!  Do you have any more info on that? Static...not cheeseburgers. 

Well electrostatic discharge typically produces punctually overheating in the semiconductors structure. This may result in an immediate failure if a connection is cut as a result of the overheating. But also it is possible that it will melt only partially. So the electrical characteristics (i.e. leakage currents) may change. This reduces the lifetime of the part. i.E. a component that had an original lifetime of 100 years may get a reduced lifetime of just 10 years or only a few weeks. For a manufacturer such a lifetime reduction may increase the returning devices during a guarantee period. It is normal that there are some failing devices, i.E. 1% during the first 2 years. If this increases to 2% due to static damage it will be a very expensive thing for larger production lines (double of the work).

One quote i found: "Analysis of non-conforming or defective devices showed that 60–75% were damaged by EOS (electrical overstress) or ESD. This rises to 90% for newer technologies. About 70% of these failures were attributed to damage from incorrectly grounded people.

Toshikazu Namaguchi, Hideka Uchida
EOS/ESD Symposium 1998 pp.245-251."

[DanielS]

Well electrostatic discharge typically produces punctually overheating in the semiconductors structure.

Overheating? With the amount of heatsinking provided by the rest of the device body, spontaneously injecting a few mJ in a relatively beefy IO pin (compared to other active elements within the rest of the IC) is not going to cause much local heating but raising a 2V gate's voltage to 20V might bust it.

I would be far more worried about dielectric breakdown within the chip or possibly blowing the clamping capacity of input/output diodes.

[george graves]

I guess that brings up the question of....how in the world would you ever test that?  Build 1 million units, and subject 10% to a static charge, and then wait 10 years for it to fail, and collect stats on it?

[schopi68]

You can do statistical projections of actual failures. Also you can do artificial aging of the devices (climate chamber).
The reason for an failure can be determined by doing microscope examination of the failed parts (and yes, i know that i.e. HP did such examinations already in the 1980s).

[schopi68]

Overheating? With the amount of heatsinking provided by the rest of the device body, spontaneously injecting a few mJ in a relatively beefy IO pin (compared to other active elements within the rest of the IC) is not going to cause much local heating but raising a 2V gate's voltage to 20V might bust it.

Here you can find a simplified description of this (and other) failure mechanisms.
www.semtech.com/images/datasheet/si96-11.pdf
As you can see almost every failure mechanism is the result of overheating/burnout.

[coppice]

Well electrostatic discharge typically produces punctually overheating in the semiconductors structure.

Overheating? With the amount of heatsinking provided by the rest of the device body, spontaneously injecting a few mJ in a relatively beefy IO pin (compared to other active elements within the rest of the IC) is not going to cause much local heating but raising a 2V gate's voltage to 20V might bust it.

I would be far more worried about dielectric breakdown within the chip or possibly blowing the clamping capacity of input/output diodes.

If you look at electron micrographs of zapped chips you seldom see pinholes punched around the I/O ring. They are normally somewhere deep in the logic.

[DanielS]

www.semtech.com/images/datasheet/si96-11.pdf
As you can see almost every failure mechanism is the result of overheating/burnout.

The document does not state a proportions between causes or links between them.

Oxide/Dielectric breakdown is listed as the first cause and is likely a factor in several instances of all three others.

[schopi68]

As described in the document dielectric breakdown also results in overheating and possible shorting. So the proportions are not relevant.

[george graves]

How about someone try to zap a part by rubbing your feet on a rug, and then do before and after tests?  Dave? 

[digital]

Why take a chance of zapping any component? It is industry practice to work in a static free environment.My last employer would instantly dismiss any employee not using static free equipment.Regards Wayne

[sotos]

How about someone try to zap a part by rubbing your feet on a rug, and then do before and after tests?  Dave?

I’ll try to do this. I will rub my feet on plastic on carpet, take a sensitive cmos chip, and touch all the pins and then test it if it’s still working.

[schopi68]

I’ll try to do this. I will rub my feet on plastic on carpet, take a sensitive cmos chip, and touch all the pins and then test it if it’s still working.

Well... if the device failes you have proven that static electricity may damage a device. If it does not fail immediately, you still do not know anything because:
- you do not know if you really had some static charge while doing the experiment
- you do not know if the chips characteristics are still in spec (without very detailed testing)
- you do not know if the chip will fail prematurely during the next months or years as a result of the discharge

Testing this way is a little bit like throwing lighted cigarettes into a forest: if it does not begin to burn you still cannot say that it will never burn. But you can trust the firefighters telling you that this sometimes will happen. 

Here is an interesting video with a real test (just ignore the product demo information  ):

In this video you will see a few snippets showing interesting facts (i am sorry, i could not find better videos with more in deep information for free):

[zapta]

My last employer would instantly dismiss any employee not using static free equipment.Regards Wayne

'last'? What happened? You didn't use static free equipment?

Just kidding.

[zapta]

[Here is an interesting video with a real test (just ignore the product demo information  ):

Wow! This is a damaged resistor. I always assumed that only CMOS and similar semi conductors are at risk.

[sotos]

What about clamping diodes, what are they for? They are for protection I know, so if somebody is charged, aren’t they for discharging him?

[schopi68]

Clamping diodes are mainly to protect the assembled device. The clamping diodes are designed to work by draining the charge into a larger external capacitor or to main's earth/the power rail. As long as the correct surrounding circuit is not connected, the charge will go anywhere... but not the intended way as this does not exist at this time.
(i.E. from the input through the clamping diode to the chips internal power rail and back into the other parts. )

This is why it is so much more important to take ESD-protection into account on disassembled devices or single components. A well designed device is able to drain/withstand normal ESD-Levels (see the Human Body Model) at the time it had been assembled. Before that its parts are susceptible for damage due to electrostatic discharge.

[Trinity]

You guys have convinced me to pick one up, and it's on the way.

As a quick followup question, I see all sorts of cleaners that claim to be especially designed for ESD mats, but is there any reason I can't just use Windex, isopropyl, or water?

[zapta]

You guys have convinced me to pick one up, and it's on the way.

Hopefully it's a rubber one ;-)

[SeanB]

Plain water works best, and if needed a drop of plain dishwash liquid followed by a rinse with plain water. Anything else runs the risk of degrading the rubber or leaving a film on it.

[zapta]

They are not expensive and last long time.

http://desco.descoindustries.com/DescoCatalog/WorksurfaceMats/MatAccessoriesCleaners/ReztoreAntistatic/10435/#.U_OgbXWx3UY

The foam makes it easier to wipe grippy rubbery mats (vs. plain water).

[schopi68]

As i can see in the product datasheet the Reztore Cleaner contains mainly water (60-100%) and isopropanol (5-25%).

As isopropanol does not affect most of the plastics used, i wouldn't have any concerns in using it.
(Isopropanol harms soft-pvc and Styrol-Acrylnitril as described here on page 15 - sorry for using the wrong language document - http://www.kuhnke.de/fileadmin/templates/content/Automation/Branchen/Medizintechnik/764343chemische_bestaendigkeit.pdf ). 

A mixture of at least 50% water and 50% isopropanol has a better cleaning result than using it pure.

[Trinity]

Hopefully it's a rubber one ;-)

3M multi-layer rubber, yes. 

[Trinity]

A mixture of at least 50% water and 50% isopropanol has a better cleaning result than using it pure.

Why is that?

[pinkman]

Lots of good points in this thread.

Keep in mind that ESD damage can be cumulative, i.e. it may not be evident right away.  So, if you're working on anything you know is ESD sensitive which you will ultimately be sending out into the world for someone to use, always use proper ESD handling procedures.

If you're just doing personal test work at home/office and don't care, then do whatever is convenient and see what happens.  I do this.  About once a month, I end up with an IC that either stops functioning completely, or ends up with a pin that sinks waaaaay too much current.  The likely cause is ESD damage.  Once in a while I know it is EOS due to general carelessness with test leads and such, but more often than not, I am sure that I have not EOS'ed the pin and the only logical explanation is ESD damage.

[schopi68]

A mixture of at least 50% water and 50% isopropanol has a better cleaning result than using it pure.

Why is that?

afaik there are two main reasons:
- pure isopropanol evaporates to fast. So you need much more isopropanol (and the dissolved contaminations may be dried again bevor they are wiped up).
 The mix is much more volatile than water alone (lower boiling-point) - so it is drying faster than pure water.
- some contaminations are only watersoluble (i.e. salts).

BTW: it's better to use distilled water - so you do nat have to mind about residues.
In practice i decide how to mix up based on the intended use. To clean up from colophonium residues i use pure isopropanol, to clean up cases or front plates i use distilled water, to clean up the ESD-mat i use almost everything.

Apropos of colophonium residues - this would be a good new thread: In older HP repair-manuals i found references that it may be better to not clean up soldering residues after repair (depending on the flux used) because this can spread up and activate aggresive ingredients instead of removing them.

[sfiber]

I use strip and esd mats with together.There is a ground jack to make ground connection.I use them because of I own,but sometimes I am working with ssop chips and this products can be necessary to be sure.