c. SOME ESD MTL. SUPPLIERS CLAIM THAT COPPER MESH GRID IS NOT REQUIRED IN CASE OF TWO LAYER FLOORING. IS IT CORRECT AND IF SO, WHY ONLY IN CASE OF THREE LAYER ?
d. WHAT IS THE RECOMMENDED SIZE OF THE COPPER GRID WHILE DOING THE ESD FLOORING AND WHAT SHOULD BE THE THICKNESS OF THE COPPER FOIL?
Well, we have a variety of bench and flooring mats and runners.
The two and three layer mats would generally refer to our bench or table mats. Our Duro-Stat line is actually a homogenous vinyl ESD matting with great mechanical and electrical properties. But most BM’s are of the two-layer or three-layer type. The top layer would give the mats its resistance to chemicals, resistance to solder, flux, and the ability to keep it clean. The backing would typically promote an anti-skid and durable surface. The three-layer mats are going to have a conductive scrim center layer and work well with most wrist strap constant monitors.
b. WHICH ONE WILL BE ADVISABLE FOR FLOORING ?
For floor mats and runners, we’ve got our UltraCon Floor Mat which is made of highly conductive rubber. Your flooring mats and runners are going to be typically homogenous and don’t have layers per say. Our Tough One line is made of embossed homogenous solid vinyl. The exception being our Anti-Fatigue II line. This static dissipative mat is a vinyl mat with a foamed vinyl backing. Our No-Slip II is made of a corrugated slip-resistant vinyl.
This question may be off topic. It sounds like you are talking about ESD flooring, not bench or floor matting. If that’s the case, well some manufacturers of esd flooring make a conductive backed tile or sheet good. This backing may be so conductive and along with a conductive esd adhesive, they claim that you don’t have to lay down an expensive copper grid. That’s fine. But if I’m installing the floor, I’ll use copper (or aluminum if requested) tape and run a standard grid the length of the room (along the x-axis) and cross it up (y-axis) so as to ground the floor at least once every 2500 square feet or a couple of times per room minimum. I’ve found that this helps prevent hot spots from tile to tile or gives more consistent RTT (Resistance Top-to-Top or Point to Point). One roll of copper tape would enable me to ground a room that was 60’ x 40’ without a problem. If I have more tape to use, I’ll use it. A liberal amount of copper tape and ESD adhesive is provided free of charge with the purchase and installation of an ESD floor from Ground Zero Electrostatics, Inc.
Copper mesh grid just doesn’t apply to 2 layer or 3 layer mats. They use ground cords. One per every 10 feet, I believe.
Copper tape comes in varying widths and typically comes in 108’ runs. Our copper tape has an adhesive backing to it that enables you to run it the length of the ESD floor. There is a spec for how thick the copper is and how thick the adhesive is in mils, but what is most critical is how conductive the tape is across its length and from top side to adhesive side. It’s pretty conductive stuff. We’ve found it to be less than 0.025 Ω in the field using a 4 lead resistance meter. The scientists have more precise data, but that it measures less than 0.1 Ω from earth is what is necessary. You can select between ½ “, 1”, 2”, and 3”, 6”, and 12”. The ½” tape is sufficient for most applications, but I prefer the 2” type.
e. WHAT SHOULD BE MIN. ESD EARTH RESISTANCE AND VOLTAGE ?
RTG and PTP resistance needs to be between 2.5e4 and 1e06 Ω for conductive and from 1e06 to 1e09 Ω per ANSI/ESD S20.20-1999 via ANSI/ESD S7.1-2005 or the combination of a person wearing ESD footwear and standing on an ESD floor should have a resistance to ground of < 3.5e7 Ω per ANSI/ESD STM97.1.
That’s the resistance part of your question. What should the voltage be? That’s up to you. Go to your design engineers and find out what the most sensitive electronic device is and design a floor that creates no more than ½ of that voltage threshold. At minimum, no ESD flooring system in combination with ESD footwear should create more than 100V per ANSI/ESD STM97.2. I like a floor that generates less than +/- 15 volts. I have more to learn about this testing as I have recently acquired the equipment necessary to measure Body Voltage Tests on all floorings that I install and/or test.
f. HOW DO WE DO THE COPPER MESH EARTHING IN CASE OF EPOXY FLOOR ?
That’s a nice question. You first want to profile your structurally sound and moisture acceptable (3-maybe up to 5 lbs or less of water per 1000 square feet in a 24 hour period per ASTM E-1907-97 & ASTM F-1869-98), then I’d apply my anchor coat and let that cure. Then I’d install the copper tape after all prep work was done and before you are ready to apply the ground plane coat and/or the ESD coat. If you have more than one ESD coat, that’s fine. But the copper grid has to make contact or be electrically conductive to the final ESD coating. If you’d like to connect the copper grid to the earthing, 3rd wire ground, or a grounding rod, that’s fine. Just make sure your flooring is properly bonded to a path to ground and be sure that all grounding sources are less than 1 Ω AC per ANSI/ESD S6.1-2005 7.2.1.1.
Resources:
New ESD Blog
