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05 Dec

Copper Tape and an Epoxy Floor

Q: How do we do the copper mesh earthing in case of an Epoxy Floor?

A: 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.

05 Dec

Minimum ESD earth resistance and voltage

Q: What should be the Minimum ESD earth resistance and voltage?

A: 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.

05 Dec

Size and thickness of copper foil when installing ESD Flooring

Q: What is the recommended size of the copper grid while installing the ESD Flooring and what should be the thickness of the copper foil?

A: 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.

05 Dec

Copper Mesh Grid with two and three layer flooring

Q: Some ESD material 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?

A: 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, 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.

05 Dec

Two layer and three layer ESD PVC Mats

Q: What is the difference betwen two layer and three layer ESD PVC Mat, and which one will be advisable for flooring?

A: 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.

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.

05 Dec

The difference between anti-static and static dissipative floors

Q: What is the difference between anti-static and static dissipative floors? Which floor will be better to use if I’m going to have an electronic assembly line?

A: Anti-static is not the proper term to use for ESD flooring.

Anti-Static refers to the ability to suppress charge generation or the prevention of static build up. Anti-static materials will not safely attract or decay a static charge before it randomly discharges. Anti-static material is usually indicated by an electrical resistance range, measured in ohms, of a minimum of 1E10, (10 giga ohms), to a maximum of 1E12, (1 trillion ohms).

ESD flooring systems are referred to as static conductive (more conductive) or static dissipative (not as conductive, but will dissipate charges in an orderly fashion).

Static dissipative floors: 1E06 Ω or 1 Meg Ω to 1E09 Ω. I would consider SD material to be the minimum requirement per ANSI/ESD S7.1-2005 via ANSI/ESD S20.20-2007. If you choose this flooring system, the RTG readings may be at the low end of the scale and be in the E06 to E07 range or it may be at the high end and be in the E08 range. You want to keep you flooring system clean and always below a gig ohm.

Static conductive floors: 2.5E04 Ω to 1E06 Ω. These floors are the superior choice for an assembly environment and offer the lowest charge generation and quickest charge dissipation. These floors require proper cleaning and maintenance, but will likely exceed the requirements for 20.20 throughout its lifetime.

I’d recommend a static conductive flooring system for your application. You are dealing with ESD sensitive components, raw boards, and/or sub-assemblies that have a low threshold voltage tolerance. With a static conductive flooring system and proper ESD footwear, you will have an optimal ESDS area.

05 Dec

What does ASTM F2413-05 compliant mean?

Q: What does ASTM F2413-05 compliant mean?

A: I’ve got the document from the American Society for Testing and Material Standards (ASTM) in front of me now.

They sent me a copyrighted document on June 2nd of 2005.

It’s significance and use section is pretty encompassing;

  1. This specification contains requirements to evaluate the performance of footwear for the following:
    1. Impact resistance for the toe area of footwear.
    2. Compression resistance for the toe area of footwear.
    3. Metatarsal protection that reduces the chance of injury to the metatarsal bones at the top of the foot.
    4. Conductive properties which reduce hazards that may result from static electricity buildup, and reduce the possibility of ignition of explosives and volatile chemicals.
    5. Electric shock resistance.
    6. Static Dissipative (SD) properties to reduce hazards due to excessively low footwear resistance that may exist where SD footwear is required.
    7. Puncture resistance of footwear bottoms.
    8. Chain saw cut resistance, and
    9. Dielectric insulation.

There’s a section in there that describes Performance Requirements and Workmanship, Hazard Assessment, Labeling and Identification, Marking and Compliance Requirements, and Keywords.

05 Dec

Ground Rod-to-earth resistance

Q: What should be the required Ground Rod-to-earth resistance? is it less than 2ohms or less than 25ohms?

A: I am going to consult my document on Grounding-For the Protection of Electrostatics Discharge Susceptible Items (ANSI/ESD S6.1-2005), an ESD Association standard.  I am assuming that your inquiry is to provide the bonding and grounding for the prevention of ESD in an EPA (ESD Protected Area).

From the Main(s) service equipment or AC Mains, you have the Hot or Black conductor (Let’s assume AC Single Phase 120v) from the Circuit breaker panel, then you have the Neutral or white conductor coming from the Neutral bus, then you have the Equipment grounding conductor or green conductor.  The black or Hot conductor comes from a circuit breaker and goes to an AC outlet receptacle.  The white or Neutral conductor comes from a neutral bus which is bonded to an earth grounding electrode and goes to an AC outlet receptacle.  The green conductor or equipment grounding conductor comes from a ground bus and is bonded to the metal chassis or conduit.  The ground bus is then bonded to the Neutral bus.  The common point ground or bus bar is connected or bonded to this ground connection, as is various other ESD technical elements (the grounding conductors or wires from wrist straps, worksurfaces, flooring or floor mats, tools, fixtures, storage units, carts, chairs, garments, etc). 

The impedance of the equipment grounding conductor or receptacle ground to the common point ground or ESD technical element shall not be greater than 1 ohm (Ω).  I see no mention of 2 ohms (Ω) in this document, although it is noted that the ground resistance values objectives vary from industry to industry.  The telecommunications industry has often used 5 ohms or less as their value for grounding and bonding.  The goal in grounding resistance values is to achieve the lowest ground resistance value possible.  The National Electrical Code defines a ground as: “a conductive connection, whether intentional or accidental between an electrical circuit or equipment and the earth, or to some conducting body that serves in place of the earth.”  The purpose of a ground besides the protection of people and equipment is to provide a safe path for the dissipation of Fault Currents, Lightning Strikes, Static Discharges, EMI and RFI signals and Interference.

The reference to 25 ohms refers to facilities with AC Equipment Ground and Auxiliary Ground (A separate supplemental grounding conductor for use other than general equipment grounding) per ANSI/ESD S6.1-2005 6.3.2.  The auxiliary ground shall be bonded to the AC equipment ground when possible.  The AC equipment and the ESD technical elements might be at different potentials.  The auxiliary ground needs to be bonded to the equipment ground to ensure that there is no difference in electrical potential between the two systems.

05 Dec

Assuring the flooring is anti-static.

Q: We always face a problem of selling your anti-static/dissipative vinyl floors to our clients. What is the solution for client satisfaction if they want to make sure the vinyl floor is anti-static or not and if the vinyl floor works as a dissipate of current.

A: The ESD vinyl flooring that we sell, service, and install is typically manufactured from a permanently conductive, non-humidity dependant blend of conductive additives interspersed with a pure virgin solid vinyl.

Our tile is specified as static conductive (2.5E04 Ω to 1E06 Ω) or static dissipative (1E06 Ω to 1E09 Ω). The term antistatic typically refers to a range of resistance outside of industry accepted standards for ESD flooring. There are some commercial and residential applications where antistatic flooring is acceptable but would be outside of the range of Static Conductive or Static Dissipative. Antistatic often refers to products used in packaging or where materials that resist tribocharge but aren’t necessarily conductive enough to bleed off charges to ground in a timely fashion.

Attachment of a typical GZ flooring system to an existing substrate is typically accomplished via GZ-C2000-4R releasable liquid conductive fiber-loaded adhesive. There are a variety of adhesives for various types of application. Grounding of an ESD flooring system is comprised of appropriately placed copper grounding tape running beneath flooring overlayment adhesive and attached to primary electrical building grounds located throughout the facility, as well as installation of GZ- ground plates. The primary electrical building grounds serve as the Common Point Ground or are bonded to the CPG for the ESD flooring (ESD technical element) and comply with ANSI/ESD S6.1-2005 as per ANSI/ESD S20.20-1999.

05 Dec

Wrist straps according to EOS/ESD standards.

Q: We have an ESD tile floor in our testing lab. During a recent AS9100 audit we were asked why we don’t use wrist straps. Since our ISO9100 & 2 certified calibration provider only uses them when they have to certify the repair of a system and we don’t do that do we need more than the flooring? (booties, straps, etc.)

A: The answer to your question is, YES. In accordance to EOS/ESD standards, an ESD floor in conjunction with Heel Grounders, ESD Booties, ESD Foot Wear does NOT take the place of using Personnel grounded Wrist Straps at the workstation. So the basic ESD program would include the technician wearing a Wrist Strap.

Protective personnel grounding products such as; heel straps, booties and shoes working in conjunction with an ESD floor are designed for processes within your ESD program where the technician has to be mobile within an ESDPA, (ESD Protected Area) where the electrostatic sensitive device is not protected in an ESD protective container or shielded in some manner, e.g. ESD Bag, Bin, Tote, Box, Tray, Container, etc.

If your process has technical personnel setting or standing at a workstation they DO require grounding via a Wrist Strap. So one doesn’t necessarily take the place of the other, and both may be required depending on your personnel and their mobility throughout the plant.

If your technical staff removes their wrist strap to transport an ESD sensitive device or component outside the ESD protected area, the device also needs to be shielded as well as the technician being properly outfitted with ESD shoes, booties or heel straps. Within the ESDPA, they do require the additional shielding protection of the device, but it is always a good idea when practical.

I hope this helps address your question, please let us know if we can be of further assistance with any ESD questions or ESD protective product requirements you and your team may be sourcing.