Author Topic: How important are ESD mats?  (Read 22811 times)

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Offline TrinityTopic starter

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How important are ESD mats?
« on: August 13, 2014, 03:17:09 pm »
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?
 

Offline Rick Law

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Re: How important are ESD mats?
« Reply #1 on: August 13, 2014, 07:24:30 pm »
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
 

Online nctnico

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Re: How important are ESD mats?
« Reply #2 on: August 13, 2014, 08:50:27 pm »
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.
There are small lies, big lies and then there is what is on the screen of your oscilloscope.
 

Offline TrinityTopic starter

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Re: How important are ESD mats?
« Reply #3 on: August 13, 2014, 10:57:43 pm »

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.
 

Offline TrinityTopic starter

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Re: How important are ESD mats?
« Reply #4 on: August 13, 2014, 11:00:48 pm »

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.
 

Offline DanielS

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Re: How important are ESD mats?
« Reply #5 on: August 13, 2014, 11:08:32 pm »
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.
 

Offline TrinityTopic starter

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Re: How important are ESD mats?
« Reply #6 on: August 14, 2014, 05:11:20 am »
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.
 

Online coppice

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Re: How important are ESD mats?
« Reply #7 on: August 14, 2014, 06:07:34 am »
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.
 

Offline VK5RC

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Re: How important are ESD mats?
« Reply #8 on: August 14, 2014, 06:22:49 am »
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.
Whoah! Watch where that landed we might need it later.
 

Offline luky315

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Re: How important are ESD mats?
« Reply #9 on: August 14, 2014, 07:43:08 am »
Full ESD protection is important to distinguish between amateurs and professionals :-)
 

Offline larry42

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Re: How important are ESD mats?
« Reply #10 on: August 14, 2014, 10:03:39 am »
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 (!))

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Offline george graves

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Re: How important are ESD mats?
« Reply #11 on: August 14, 2014, 10:22:25 am »
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. 


Offline JuKu

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Re: How important are ESD mats?
« Reply #12 on: August 14, 2014, 10:30:35 am »
Strap protects everything you touch, but does nothing for stuff touching the table.
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Offline schopi68

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Re: How important are ESD mats?
« Reply #13 on: August 14, 2014, 11:10:41 am »
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.
 

Offline TrinityTopic starter

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Re: How important are ESD mats?
« Reply #14 on: August 14, 2014, 01:06:16 pm »

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.
 

Offline Rufus

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Re: How important are ESD mats?
« Reply #15 on: August 14, 2014, 01:56:27 pm »
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.

 

Offline nanofrog

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Re: How important are ESD mats?
« Reply #16 on: August 14, 2014, 06:41:29 pm »
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). ;)
 

Offline sotos

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Re: How important are ESD mats?
« Reply #17 on: August 14, 2014, 08:47:15 pm »
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.

« Last Edit: August 14, 2014, 08:52:06 pm by sotos »
 

Offline TrinityTopic starter

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Re: How important are ESD mats?
« Reply #18 on: August 14, 2014, 09:35:21 pm »

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.
 

Offline AG6QR

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Re: How important are ESD mats?
« Reply #19 on: August 14, 2014, 10:41:23 pm »

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.


 

Offline TrinityTopic starter

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Re: How important are ESD mats?
« Reply #20 on: August 14, 2014, 10:47:52 pm »

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?
 

Offline DanielS

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Re: How important are ESD mats?
« Reply #21 on: August 14, 2014, 11:22:05 pm »
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.
 

Offline AG6QR

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Re: How important are ESD mats?
« Reply #22 on: August 14, 2014, 11:43:04 pm »
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.
 

Offline TrinityTopic starter

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Re: How important are ESD mats?
« Reply #23 on: August 14, 2014, 11:52:11 pm »

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.
 

Offline zapta

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Re: How important are ESD mats?
« Reply #24 on: August 15, 2014, 06:34:30 am »
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.
 


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