ESD protection in work area

I'm not sure where to ask this, so I apologize if I chose incorrectly.

I have a metal table top which is rather large, separated from the metal legs by a layer of wood. I am thinking of using it for my work area. Would it be best to ground the table top and legs to avoid ESD? And would this add a risk to electric shock for myself, as I would be touching the table top regularly?

Any suggestions would be greatly appreciated.

Hi,
That is a good idea.

Your only risk is if you are working with high voltage equipment on the metal tabletop, which is not a good idea.

ESD protection is about anything coming into contact with your sensitive component not being at the same potential.
ESD mats have connections to enable a wrist band to keep you at the same potential as the mat.
mat_kit_for_benc_4f7aa308cacd9_1_1.jpg

Tom… :slight_smile:

I just looked up the mats, quite expensive. Do you thik the metal table top is sufficient?

What do you mean by high voltage? I'll be working with 5V, 9V, and 12V DC. That should be safe, right?

Also, how can I ground it? I have a metal radiator nearby, would that work? Or is the ground on a plug better?

Thanks again.

I recommend first measuring the resistance between the electrical outlet ground and the radiator. If you see a resistance, use the radiator as your ground connection.

Nope, no resistance on the rad. I just noticed my plug has no central screw on the plate. How shoul I ground in this case?

Feddar:
Nope, no resistance on the rad. I just noticed my plug has no central screw on the plate. How shoul I ground in this case?

Well at this point, I have to ask what country you're in. The electrical outlets are quite different around the world.

Canada. I just tried to test ground (on a 12V adaptor) to the plug ground, and the adaptor started smoking. It's toasted. I guess that was wrong...

The funny thing is that when I did that, the resistance meter showed no resistance (ie infinite resistance).

How many pins ?

3 rd pin in uk is normally plastic.
Neutral is normally bonded to earth here.

Wall warts generally though are insulated (floating output).

EDIT

Whatever your source of earth i suggest a 1 megohm resistor so that if you touch something live the current is limited.

3 pins.

I measured the resistance between the 3rd pin (ground ) and the -ve on the wall wart. I figured they would be the same. But the wall wart got toasted. That shouldn't happen, should it?

When you say the wall wart has a floating ground, does that mean its ground is not the same as the true ground? And so I established a connection between the two, and that caused a short of sorts and toasted it?

Normally there is no connection between mains earth and the negative of the wallwart.

They are totall insulated.

I have no idea why yours is toast.

Measuring resistance should have no effect unless you perhaps used a 1 KV megger test,

If its chinese however its anyones guess

The multimeter is fine. Strange.

I understand now. The radiator is indeed grounded. I'll use that. It is mostly painted, so I guess I should solder a lead to an exposed part.

Or is grounding to the wall plug better? (Conceptually, I have a problem hooking myself up to a ground plug...)

You are going to need a gigantic soldering iron to solder to a radiator. There is actually a big set of electrical standards on grounding house wiring which says specifically not to use solder.

The mats for the tabletop are surprisingly expensive. But when you think about what the mat does, you may appreciate the cost. It has a low resistance across the pad, so the earth connection in one corner is distributed across the whole pad but it has a high resistance between that and the surface so it cannot conduct dangerous currents through you. It also has to be a tough work surface that can handle the heat of a soldering iron.

Static protection requires resistors which are ordinarily thought of as "high resistance" like a megohm or more. This is quite adequate to conduct away the static charge but if you accidentally touch live mains wires and your 'protected' bench top, the current through the resistor is harmless to your body. If you get a low resistance between the table top (like 10 ohms or less) and true earth then that is not good for your safety.

If you have any mains powered equipment with an earth pin in the cable and a metal case, then the case will have a low resistance to earth. Join that to your bench top with a resistor - it can hide under the case.

Feddar:
I'm not sure where to ask this, so I apologize if I chose incorrectly.

Any suggestions would be greatly appreciated.

I'm positive there will be plenty of people to disagree with me, but I'd recommend not using any ESD protection before using a metal surface on your electronics bench.

If you use no ESD protection, the chances are that you'll have a handful of genuine ESD failures in your life. I'm sitting in the R&D office for a leading IC manufacturer right now...every desk has dozens of unprotected chips on them...we have almost no unexplained IC failures in our workday. In our factory, we take ESD seriously, so that we can ensure six sigma quality over the life our of product. In R&D and when hobbying, however, I rarely take ESD precautions (only for things like handling my $1k video cards). If 100% of my unexplained failures actually did turn out to be ESD, (keep in mind that 90% of the ICs returned for "ESD failures" turn out to be something else when FCA is performed) then I've had maybe 5 over 20 years.

As for a metal table, you are almost certainly going to have a battery short on it someday, or a pcb will have a tool or a loose component short some part of it to ground, or worst case shock high voltage to ground through your body. While I haven't checked the OSHA standards, I'd guess that a metal surface would be illegal for an electronics workbench.

I have one that is 18 * 24 inches on my desk. Seems to work well - the prices seem to have really jumped, but this one is similar to the one I have: http://www.amazon.com/StarTech-com-24x27-5-Inch-Desktop-Anti-Static-M3013/dp/B00009XT3H/

A metal bench top is bad because it shorts things out if you are working with a live board on it. The trick is to have a mat that is conductive enough to bleed off any static charge but not short things out. As far as ESD danger goes, on thing I have not seen mentioned (and it is an important part of ESD handling) is the humidity in the room. Those in very dry areas will find they zap things all the times while those where the humidity is much higher have much less problem (it also depends on what floor covering etc. you have. You should have an ESD mat that is grounded through a resistor to limit potential dangerous currents, you should also be grounded (or at least touch the mat before touching anything else) and things like the soldering iron typically need to be grounded. There is a whole big collection of information on how ESD protection etc. needs to be set up in a commercial environment (we had all sorts of rules/regulations etc. including conductive mats, conductive envelopes boards / parts went in, humidity control etc. when I was working with avionics boards at Boeing).

Thanks. I ordered one. The cheapest I had seen before was $200-500.

good price that thanks , ill have one myself.

I think someone like 3M used to make a spray on dissipative coating, anyone knoww.

I could be confusing with fire retardent though.

EDIT

I know of lots of these advertised but am looking for one specifically for component handling, with provable long term effect.

Just get one of those overhead “misters” like they use in the produce department to keep everything wetted down. That will control the problem :slight_smile: Typically we also had a conductive mat on the floor and an area marked off with tape that you did not enter unless you were grounded before working with components/boards (for some reason, folks get very sensitive about boards that involve flight controls - go figure!! )

Feddar:
I’m not sure where to ask this, so I apologize if I chose incorrectly.

I have a metal table top which is rather large, separated from the metal legs by a layer of wood. I am thinking of using it for my work area. Would it be best to ground the table top and legs to avoid ESD? And would this add a risk to electric shock for myself, as I would be touching the table top regularly?

Any suggestions would be greatly appreciated.

you are confused about ESD. YOU will be the source of any static electricity, not the table or your equipment. Your clothing and movement will generate the charge. Your grounded table will only conduct it away if you touch it.

Your charged body and clothing act as one side of a capacitor. Just bringing your charged body/clothing near a sensitive component will cause an equal but opposite charge to flow to the component.

You must eliminate the charge at the source to be effective. What has been described are just band aids. A proper conductive floor will drain away the static charge on your body if you use ground straps on your shoes. We have clean, bare concrete floor at the plant. Other floors, such as tile can be coated with conductive layers and they can be connected to an effective ground.

Some protection from the capacitor effect can be given by wearing a conductive lab jacket.

The easiest protection for a home shop is to use a wrist strap connected to a 1 meg resistor which is connected to ground.

We do all of the above because we live in the high desert with winter humidity of 10% or lower.

Paul

I just figured I would use the table to ground myself and other components (not ICs). I sit on a stool and have my feet on the lower part of the table, which is also grounded.

Humidity taken care of. Thanks.

I started today working on a breadboard. I am leaving the soldering for when I get my mat. I sure can see how a metal table is not a good idea. I am being very careful with the wires and power supplies, and the constant thought about potential shorts is interfering with my concentration on the task at hand. I look forward to using the mat and not worrying about it as much.

There is so much to the electrical work. Great fun, but so much to it. Design, shopping for the best parts, PCB design, making boxes and arranging controls, soldering issues, ESD issues... I hope the first real project is the hardest.

Feddar:
I just figured I would use the table to ground myself and other components (not ICs). I sit on a stool and have my feet on the lower part of the table, which is also grounded.

Humidity taken care of. Thanks.

I started today working on a breadboard. I am leaving the soldering for when I get my mat. I sure can see how a metal table is not a good idea. I am being very careful with the wires and power supplies, and the constant thought about potential shorts is interfering with my concentration on the task at hand. I look forward to using the mat and not worrying about it as much.

There is so much to the electrical work. Great fun, but so much to it. Design, shopping for the best parts, PCB design, making boxes and arranging controls, soldering issues, ESD issues... I hope the first real project is the hardest.

Just take care so YOU don't become part of the circuit!!

Paul