I need some expert ESD mitigation assistance. We have recently discovered that our production facility’s concrete floors were sealed with a conductive epoxy when our building was constructed. The floor taken 15 years of wear. A measurement to earth ground (or from any two points) from anywhere on the floor yields a 1x10^8 ohms (100,000,000 ohms or 100 MegaOhms).

We use a variety of benchtop mats that measure from 10^7 to 10^8 (10,000,000 to 100,000,000) ohms to earth ground. Combined with these is a wrist strap system that is 1 Meg from wrist to mat.

We use a variety of floor mats that measure from 10^5 to 10^6 (100,000 to 1,000,000) ohms to earth ground. Combined with these is a heel strap system that is 1 Meg from ankle to floor mat.

We have several areas where the floor has conductive paint whose measuremnet to earth ground (or from any two points) from anywhere on the floor yields a 1x10^5 to 5x10^5 ohms (100,000 to 500,000 ohms).


Supposedly, the use of the floormat/heel strap allows a person to work safely on a product on the bench mat without the wrist strap. All of the mat and floor measurements have been taken using the same ESD surface test equipment.

Summary:

Bench mat system 11Meg to 101Meg from wrist to earth
Bench mat system 10Meg to 100Meg from any product on the mat to earth.
Floor mat system 1.1Meg to 2Meg from ankle to earth.
Painted floor 1.1Meg to 1.5Meg from ankle to earth.
Epoxy floor ~101Meg from ankle to earth.

Question:
Do we really need conductive floor mats?
Is it a correct assumption that product on the mat can be safely manipulated while wearing only heel straps on the floor mat? Painted floor? Epoxy floor?
Is it a correct assumption that product at earth ground can be safely manipulated while wearing only heel straps on a floor mat? Painted floor? Epoxy floor?

You can find the answers to your questions in ANSI/ESD s20.20-1999, available free of charge at www.esda.org (http://www.esda.org).

:thanks: Al. I knew somebody here could point me in the right direction.

Any help with replies here would be nice, too.

Any help with replies here would be nice, too.In a nut shell:
Where unprotected ESDS devices are handled, a grounded static protective worksurface with a resistance to ground of less than 10^9 Ω must be used.

Grounded flooring or floor mats are only required when personnel or mobile ESD protective workstations utilize floor grounding methods.

Each person handling or within twelve (12) inches of unprotected ESDS devices must be grounded using either:
a) Wrist straps that:
1) Provides a continuous electrical path from the user directly to ESD
ground.
2) Have an integral resistance at the wrist band end of the grounding wire that will limit current to less than 0.5 mA through that specific path to ground at the highest power supply voltage that may be encountered.
3) Be worn by operators handling unprotected ESDS devices when seated.

b) ESD protective footwear (heel straps, toe straps or shoes) that:
1) Provide a continuous electrical path from the user directly to the ESD protective flooring or floor mat.
2) Be worn on both feet.
3) Limit current to less than 0.5 mA through that specific path to ground at the highest power supply voltage that may be encountered.
4) NOT be relied upon for grounding of seated personnel.

Yes, relying upon the epoxy and/or painted floor is adequate. The foot straps are adequate as long as the strapped foot (feet) remain on the floor. If an operator sets down they should either be setting on a grounded (via chains, straps, etc.) chair, or implement a wrist strap.

These are the conditions we are currently working under - although we do implement the use of ESD floor mats where an operator is going to be on their feet much of the time in a specific area (for operator comfort, not additional ESD control).

Thanks for the replies in plain English. What I was really concerned about was a situation were the resistance to ground was 100 times larger from the product to ground than the person to ground. It doesn't look like it matters as long as:
a) "Ground" is less than 1 ohm from "Earth Ground"
b) Person to "Grounding System" is < 35 x 10^6 ohms
c) "Grounding System" to ground is < 1 x 10^9 ohms

We use the painted floor for low resistance to ground in our automated electronics assembly area since product must be handled without Faraday cage protection to get it from the line into the protection.

The floor mat usage developed when people wanted to stand and work on the final assembly lines without being tethered at the wrist. At that point, many years ago, we were not measuring or testing our mats, floors, or straps. Here people are removing PCBs from protection and placing them in final product that is resting on a protected surface.

Now that we regularly test mats, floors, straps, etc. for compliance, the conductive epoxy sealer was discovered on the concrete. The only way to know is to test because this was not documented in the building specifications nor was anyone aware that such a sealer had been applied. It looks like we've just freed our work force from the wrist strap without spending $200 a pop for 4'x8' floor mats or conductive paint at ~$1 per square foot (over about 15k square feet).

We have wrist straps and heel straps (plural, both feet) that are tested daily on everyone in the production area. They also wear semi-conductive smocks and protective eyewear. Every bench has an anti-static mat connected to ground with a wrist strap port. Every cart has a metal drag strap and is made for electronics handling. Every PCB is in some sort of Faraday cage, either in an anti-static bag or in an anti-static tote with lid, unless it is being transfered from production line to storage or storage to production line. Unplugging everyone that is standing (just not necessarily on a mat) is going to make some folks very happy.

I used to work for a company in Marietta, OH that manufactured electrostatic dissipative mats sold to U.S. Government for Navy Nuclear subs.
Each roll was 100% tested and the Gov't. inspector came in from Columbus, O to check each shipment and documents of test results. Company name is RJF International (formerly a B.F.Goodrich plant bought by a private owner)
Good company.

Another thing that I have learned from all this: If you create a conductive surface that measures less than 10^6 ohms from any two points and is larger than 20 square feet (~1.86 square meters), this surface essentially becomes earth ground. Sinking large copper rod into the earth not required.

If an operator sets down they should either be setting on a grounded (via chains, straps, etc.) chair, or implement a wrist strap.
Please don't say grounded chair. Wrist straps are $25 and I have a hard enough time keeping those on peoples' arms.
The first chair that came up on google (http://www.hmcelectronics.com/cgi-bin/scripts/product/1060-0031/) is $286! And that assumes that it actually works through 3 or 4 layers of polyester clothing.

Another thing that I have learned from all this: If you create a conductive surface that measures less than 10^6 ohms from any two points and is larger than 20 square feet (~1.86 square meters), this surface essentially becomes earth ground. Sinking large copper rod into the earth not required.

Yeah, Icy if you get to thinking about it, How far do you have to sink a ground rod for a ship at sea to become "grounded"? And where is my grounding rod for my TV, computer, stereo, et cetera? When you work on your TV, computer, et all do you strap to earth ground, or do you strap to chassis ground (most appliance manuals refer to strapping to chassis ground)? Isn't the point really to make sure that the equipment, devices, and you are at the same realive potential?

Please don't say grounded chair. Wrist straps are $25 and I have a hard enough time keeping those on peoples' arms.
The first chair that came up on google (http://www.hmcelectronics.com/cgi-bin/scripts/product/1060-0031/) is $286! And that assumes that it actually works through 3 or 4 layers of polyester clothing.You can buy antistatic spray for the chairs. An ESD program never seems to end.

Here's a recipe for homemade antistatic spray (http://www.recipegoldmine.com/house/house17.html) that you can use on fabric.

Dave and Al,
You've hit the nail on the head. This isn't about meeting a standard for me. It's about "assurance". Are you REASONABLY assured that you are not damaging your product with electro-static discharge? It IS a relative potential thing.

I have upgraded my $1,000 computer at home with a $100 additional hard disk drive, a better DVD-RW drive @$80 , a higher speed DVD reader @$40 , and faster video card with twice the memory @$40. I wrist strap myself to the computer chassis and then pull the cards or drives from their anti-static bags and plug 'em in. I've never damaged anything. Believe me, at those prices, I don't want to even come close.

At work, I need to have some specifications (i.e. data) to PROVE TO A TS AUDITOR that I am reasonably assured that I am not damaging anything. In God We Trust, all others submit data.

Here's a recipe for homemade antistatic spray (http://www.recipegoldmine.com/house/house17.html) that you can use on fabric.Of course, at work, you need an MSDS for the fabric softener, ammonia, and probably the water, too. Now you're helping too much, Al.:biglaugh:

Of course, at work, you need an MSDS for the... water, too. Now you're helping too much, Al.:biglaugh:
Better have a look here, just to be safe: Dihydrous Monoxide FAQ (http://www.dhmo.org/facts.html)

Better have a look here, just to be safe: Dihydrous Monoxide FAQ (http://www.dhmo.org/facts.html)Jim, that's so old it's growing hair.

Jim, that's so old it's growing hair.

Well, it smelled OK to me.:D

Boy, oh, boy. Once you get your questions answered, things digress pretty rapidly around here.:tg:

Question:
Do we really need conductive floor mats?
Is it a correct assumption that product on the mat can be safely manipulated while wearing only heel straps on the floor mat? Painted floor? Epoxy floor?
Is it a correct assumption that product at earth ground can be safely manipulated while wearing only heel straps on a floor mat? Painted floor? Epoxy floor?
No, coductive flooring is not a must.
No, it is not a correct assumption that product on the mat can be safely manipulated while wearing only heel straps on the floor mat as it will also depend on the device sensitivity level.

There are bascially 3 principles to proper ESD control.
1. All conductors must be grounded.
2. All insulators must be isolated or neutralised.
3. Prevention. Example, through providing proper training to all concern.

Wearing heel straps only does not guarantee that the devices or products are protected from ESD events as there will still be charges generated and through what I've seen, the voltage could go as high as 70V to 90V and if your device or product sensitivity level is relatively lower, e.g. in some IC, the HBM level could be as low as 10 - 20 V, in this case, it will be a real concern.

I would suggest that you continue to put on your wrist strap even with ESD footwear on to give you the added assurance that if somehow or rather, your device or product becomes more sensitive to ESD.

Understanding and complying to ANSI/ESD S20.20 will definitely give you the added value to a well protected ESD safe workplace. It is definitely NOT just about getting a certificate.

thks.
jeffrey.:)

Every cart has a metal drag strap and is made for electronics handling.

:topic: Becareful with drag chains because typically they are not heavy enough to make good contact on the floor or if they are heavy enough they are not long enough to make good contact on the floor. Also if they are multiple level carts do you loose connection where it is joined at each level? I learned the hard way... Customer pointed it out!:o

:topic: Becareful with drag chains because typically they are not heavy enough to make good contact on the floor or if they are heavy enough they are not long enough to make good contact on the floor. Also if they are multiple level carts do you loose connection where it is joined at each level? I learned the hard way... Customer pointed it out!:o

For drag chains, the problem is that it will accumulate dirt easily upon frequent movement, in a typical class 10K environment, it will only take approx. 1 month for the chain to get real dirty and resulted in intermittent poor grounding. Of course, it will be much better in a class 100 or 1000 environment.
For multiple level carts, to ensure connection between each level, conductive clips or collars are installed at each corners of the joints. This will give you a good grounding path.
I would strongly suggest to avoid using drag chains but instead go for conductive castor wheels for mobile carts or trolleys. All the trolleys and mobile carts in my factory are with conductive wheels and so far even when it accumulates dust, it doesn't fail. I've been using it for easily 2 years with NO cleaning of the wheels and yet it works fine. Setback is conductive wheels are a lot more costly.
thks.
jeffrey.

Basically,the purpose of esd control is to protect esd sensitive device from being damaged by ESD.
The source of ESD damage comes from people, machine and materials that the esd sensitive come into contact with.
As to protect static damage from people, we need to wear anti-static wrist strap whenever we handle esd sensitive component in seated position and esd shoes whenever we handle parts in standing position. This is to drain the static charges through the wrist strap and esd shoes. However, esd shoes only work well when it is worn with the presence of static control flooring,i.e esd floor mat or conductive flooring.
The resistance to ground of the system ( man, esd shoes and flooring) should be less than 35M in order to have voltage build up on the person to be less than 100Volt.

As more material where the esd sensitive may come into contact with or placed on, the material worksurface to ground should be less tahn 1x10E9 ohm.This is to ensure the static charge is drained to ground at rate which is not too fast or too slow.

For grounding and bonding system : all the esd material for example esd mat, wrist strap outlet or plug, esd floor mat etc should be bonded at the same common point. The resistance from this point to the equipment ac ground should be less than 1 ohm. And impedance less than 1 ohm from ac equipment ground outlet to the neutral bond at main service entrance.
This less than 1ohm requirement is to ensure good bonding system existence so that charges flow to ground through the bonding system quickly.

More of the requirement can be download for FREE at http://www.esda.org.

As for cart, the chain would not serves much purpose as the good contact usually comes from the caster conductive wheels.


Training and periodic audit is important to ensure people in the factory understand the impact that ESD has on the product. Visual aids on the esd control may be a good idea to impart the controls that you want to set.
Hope that helps.

We use a metal wire rack type cart. Our original carts were all put together with the standard plastic holders on the corners. We tore them all down some years ago and replaced one holder on each shelf with a metal holder. I have tested every cart to make sure that every shelf is connected to ground (i.e. our conductive floor).As for cart, the chain would not serves much purpose as the good contact usually comes from the caster conductive wheels.The best part about the Cove is that we get a rebuttal to statements like this.
We made our drag chains. They consist of your basic hardware store dog chain, fastened to the bottom shelf with a bolt, with another bolt fastened to the loose end of the chain to provide good contact with the floor. The chains are long enough to drag multiple links but short enough to stay out from under the wheels. The bolt on the end of the chain tends to move around such that the same side of the chain isn't always dragging. I believe that this eliminates any dirt build-up, based on testing. I've retested the carts several times over the years, without manipulating the drag chains in any way, and they have always remained connected to ground. The conductive wheels for these things are just outrageously expensive. In addition, they are DEFINITELY susceptible to dirt build up that ends up insulating them from the conductive floor, unless you clean them regularly. I have 5 years of ESD equipment testing records that disprove your statement.

You can buy antistatic spray for the chairs. An ESD program never seems to end.

I'm trying to implement an ESD program and I am finding just that: The ESD program never seems to end. And since ESD damage is hard to detect I'm having a hard time justifying all these new requirements to our quality system.

So first question is do we need this program? I believe the answer is yes. We manufacture medical devices that contain circuit boards, and EPROMs.

Next question is how much is enough? If we have a program is it required to meet EN 61340-5-2? Do we have to measure and control humidity levels? Are wrist straps enough? Or am I telling management that the $2 components that we use require $2000 worth of new equipment despite the fact that nonconforming product has never been traced to problems caused by ESD damage...

Any help/input anyone may have would be greatly appreciated!

I'm trying to implement an ESD program and I am finding just that: The ESD program never seems to end. And since ESD damage is hard to detect I'm having a hard time justifying all these new requirements to our quality system.

So first question is do we need this program? I believe the answer is yes. We manufacture medical devices that contain circuit boards, and EPROMs.

Next question is how much is enough? If we have a program is it required to meet EN 61340-5-2? Do we have to measure and control humidity levels? Are wrist straps enough? Or am I telling management that the $2 components that we use require $2000 worth of new equipment despite the fact that nonconforming product has never been traced to problems caused by ESD damage...

Any help/input anyone may have would be greatly appreciated!
This is one of my biggest headaches as well. I feel your pain. Yes humidity levels are important. Other ways to mitigate low humidity is to use ionizers. I am not familiar with the standard you cited, but with ANSI/ESD S20.20. I attached it in the thread, ESD Control Certification by NARTE, (http://elsmar.com/Forums/showthread.php?t=9766) along with a few other documents. You may also want to look at the ESDA web site (http://www.esda.org/standards.html) as well.

Thanks Al! That ESDA link is a huge help.

ESD sensitive components are getting more sensitive to ESD damage in the coming years.

Definitely there is always a need to have a static control program.
Working as an ESD coordinator myself, our plant has been certified to ANSI/ESD S20.20 for more than 5 years now.

ANSI/ESD S20.20 standard is widely used by many companies and you can download for FREE at http://www.esda.org.
This standard will give you a guideline what is required when you set up your static control program. It is just like when we have ISO 9000 certification.
Certify your facility against ANSI/ESD S20.20 would give your customer more confidence ; you're telling your customer that you're serious about ESD.