Anti-Static precautions

[Christmas.joe]

I have a little mat, but since it's not grounded, I really don't think it provides much protection.

RM

Not true at all.  The mat even ungrounded gets you at least 90% there by providing a place where the various potentials can equalize between you and the devices if you touch the mat before working on the stuff sitting on the mat.

If you have a soldering iron that is ESD safe, you can take additional precaution by clipping a binder clip to the mat and touching the hot iron to the clip before you solder.  If you have a non-ESD safe iron, then clip a leg of a 1 to 10 meg ohm resistor to the mat with the binder clip and touch the iron tip to the loose leg of the resistor before you solder.

I was once stuck in a grass hut in the amazon, my antistatic mat was a Wrigley's gum wrapper taped to a piece of cardboard.  But that is a story for another time...

Greg

I'm sorry, but I have to caution using EDS/antistatic mats and wrist bands that are not grounded properly.

It is important to note that an ungrounded Conductive or Anti-Static Mat will retain an ESD and transfer the charge to the next object it comes in contact with.

Conductive Mats (10¹ to 10⁵ ohm) have a low electrical resistance which allows ESD to flow across its surface. When attached to an earth grounding point the ESD will flow to ground and the excess charge on the mat and individual will be neutralized.

Anti-Static Mats (10⁵ to 10¹² ohm) have a higher electrical resistance than conductive mats. Like conductive mats they will allow ESD to flow across its surface but in at a slower rate. This slower neutralization of ESD prevents damage to microcircuit devices which cannot tolerate a sudden flow of static charge from the device to a grounded mat.

Wrist & Shoe Straps - These items are designed to provide the highest level of contact with an individual and a static dissipative control device (floor mat, work surface, ground plug, etc.)  They serve strictly as a channel for removing static electricity.  Simply wearing a strap accomplishes nothing unless proper contact to a grounded static removal device or object is made. 

If you want your mat to do it's job then ground it.  If it's not grounded, then you are not benefiting from it's design to protect your hardware.

DO NOT ground it to your house wiring. The electrical ground for your house is solely for dissipating "stray voltages" from wiring faults. By wiring your anti-static system to that and if you wear a wrist strap, you'd be connecting your wrist to the same circuit. If something goes wrong in your house wiring while you're strapped into that, you and what ever is being worked on will get the results of that fault.

A water pipe (that has no PVC and most modern homes do) or radiator (old school) can be used and is a safer static ground although I don't recommend this.  The best way is go get a copper grounding rod from some hardware store, drive it in the ground as far as you can outside your work area and use that as your antistatic grounding system. 

Never Ever have this stuff connected to you while lightening is in the area or you could be fatally electrocuted.  STOP WORKING on your stuff during lightning in ALL CASES.

 

[rimist]

I live in the lightning capital of the world, so not soldering during lightning is going to take away a lot of opportunities, but I don't want to be extra crispy...

My water pipes are PVC, so that is out. I don't have radiators. House ground is also out.  dedicated copper ground rod isn't feasible for me. Can you suggest an alternative for a just starting out hobbyist?

- Rimist

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[pk]

What you want to prevent is the electrostatic discharge through the parts.  If you are at the same potential as the parts all is ok.  For example, here in Colorado we have low humidity in the winter months and it is not difficult to draw 1 inch arcs after shuffling your feet across the carpet and putting a finger near a screw on a light switch cover.  If I had the PIC in my hand and placed it near the screw until the discharge occurred, the discharge current flows through the PIC and would probably damage the part.  If I held the PIC in my left hand and discharged myself with the right hand, the PIC would not be damaged since the current did not flow throw the PIC. 

I have worked in the electronics industry in CO since 1985 and we are aware to ESD.  When handing someone a part, it is common to touch the person on the free hand to eliminate any differences in voltage potentials.  (Sometimes we feel the shock) before actually handing the part to the person. 

Living in FL with the high humidity, I doubt if you will have a problem with ESD.  Just use common sense and do not handle semiconductor devices before touching the work surface around the parts, or grounded metal like your computer case. 

[Greg]

Well, looks like I stirred some disagreement once again.

Joe on some philosophical level I can agree with much of what you say but lets face it, most folks don't have the best solution and have to settle on an acceptable or good enough solution.  The unacceptable solution is not being able to participate in this hobby.  Somewhere between utopian and unacceptable is where most of us have to live and operate.

Although I didn't directly advocate using building ground to dissapate stray charges, it is a perfectly acceptable practice and not at all dangerous otherwise grounded and/or ESD safe soldering irons would not fill their purpose very well at all.  I myself often specify isolated grounds in certain situations but that has more to do with decreasing the chance of ground loops and negating the possibility that some other cause on shared wiring could inadvertantly break the ground path than a condemnation of building ground systems in general.

Given the choice of no ground at all or utilizing an existing building ground, which would you choose?  Surge suppressors commonly installed in building power centers use building ground to great effectiveness in controlling transient over voltage conditions, unrelated to wiring faults, including induced static charges.  A person wrist strapped to the building ground is only in danger if the ground isn't functioning otherwise the guy strapped to a completely separate ground rod is connected to the same conductor (earth) as the building and electrical grid is.

Having been in the microelectronics industry for more than 35 years myself, I agree with what pk has said and stand by my previous post on this matter and can see no reason why someone without a ground option shouldn't do what they can to mitigate the potential of electrostatic damages by using an ungrounded antistatic mat to work on.

Greg

[rm357]

I agree that for home users, the electrical ground from a 3 prong outlet should be fine - just make sure that the outlet is properly wired.

My WARNING is to stay clear of the neutral (white wire) - that is not ground and should not tied to the building ground at all. In most house wiring it is the center tap from the power company's 240v transformer that feeds your house and is grounded at the transformer, but if the two phases are not equally loaded in your house, there is likely to be a couple of volts between that wire and the green ground wire...

RM

[Greg]

but if the two phases are not equally loaded in your house, there is likely to be a couple of volts between that wire and the green ground wire...

RM

And here I thought that little tingle on the wrist was just to keep you from nodding off in the middle of soldering those triacs.   

Greg

[rimist]

Just to get it out of the way: The neutral is bonded to the ground at the main switch as required by code.

Here is my setup: The outlets are wired correctly (I checked). I have an ESD safe soldering station, an Aoyue 937+ to be precise. I also have an anti-static mat, with a wrist strap. I added a binder clip to the mat to touch the hot iron to before use. My "helping hands" tool is all metal except the magnifying lens.

The questions: in order to ground the mat, I plan on using a three prong cord, cutting the hot and common flat prongs, and soldering the ground wire to the above mentioned binder clip. Will that work, or do I need to put a 1M ohm resistor between the binder clip and the cord?
Is it ok to plug the soldering station and the mat ground into the same three prong extension cord?

- Rimist
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[Greg]

I'm surmising that you're wanting to use a power strip to plug the mat ground, soldering iron and probably other stuff (light, fan, etc) into and then a 3 wire extension into a grounded outlet.  That or similar being the case, you should not use a resistor and given that you have an ESD safe iron and the mat are now grounded together by virtue of the power strip there is no benefit to touching the tip to the clip before soldering.

Greg

[rimist]

Thank you!

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[Christmas.joe]

ESD/Anti Static Mats only work (standing on them) as designed if you are barefoot or wearing EDS/Conductive shoes or the mats are on the tabletop that the hardware is being worked on, then it don't matter.  Regular shoes or wearing only non-cotton socks while your feet are on those mats are not going to help much.  And, if you are only wearing cotton socks they should be a little damp.  I'm sure for most the earth ground from the 3 prong plug fault would be useful if nothing else is feasible with a wrist strap. 

The information I provided earlier is the best way to protect you and your equipment although maybe not the most practical way for some.  Just be aware of the dangers of strapping yourself to a house ground fault circuit. There are always alternatives to the best way that will probably help in reducing damage.  I am in no way going to advocate that a homes ground fault is a completely safe alternative for wrist straps.

Just touching an earth ground before handling anything sensitive to ESD would be helpful.  It's your choice.  Just remember one thing about the third prong on your house, it is not going to save you if something goes wrong elsewhere in your electrical system.  The ground fault (third prong) of a house receptacle is designed to sense voltage on that third prong in only that one circuit, and only that receptacle will trip if you have them.  It don't detect all stray voltage in the third prong ground, only the one the devise is plugged into.  If it didn't, every-time a ground fault receptacle tripped, they all would trip and that don't happen.  It just protects (isolates) that one individual circuit and you.

I'm not a paranoid about electricity, but I do have an ESD background and it is by far the most bizarre creature in the world of electronics.     

 

[rimist]

I'm using it on the table top, with the helping hand holding the circuit board. I know my electrical system is correct, because it wasn't, and I rewired the bad parts and replace the breaker box, under the watchful eye of a master electrician.

I appreciate the info!

-Rimist