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.

05 Dec

Conductive flooring in an "explosive" environment.

Q: We are an explosives manufacturer and are looking to repaint our conductive flooring. We subscribe to the standard NFPA requirements for conductive flooring. What is the best and most economical product to apply? Consider that the environment would be expected to be consistently wet.

A: We recommended (2) possible options, both of which would be completely monolithic and seamless due to the excessive liquids that will be present.
Anytime that you have explosives present, the floor will have to be “sparkproof” and fall into a conductive range, verses static dissipative.
These are the two most important criteria for recommending a system for this environment.

Out of these (2) systems, a conductive epoxy is going to be most cost effective, verse a thermally heat welded conductive vinyl system.

Always best to consider a “professional” or approved factory installation for warranty consideration as well as certification that the floor meets the customers expectations and is actually going to get the job done.

05 Dec

How important is humidity in the control of electrostatic problems?

Q: How important is humidity in the control of electrostatic problems? What is the approximate decrease in electrostatic control if the humidity is reduced from 50% to 35% RH?

A: I have linked a white paper below for your review that puts this topic into perspective.

This data seems most relevant in this case, because it points out how well humidity from 30% and up reduced tribo-charging, but not good enough for the thin-film applications. Notice that voltages of up to 1.5 kV are still generated with ease in an 80% environment! Dropping from 50% to 35% might be beneficial to prevent corrosion, but still require an EPA (ESD PROTECTED AREA) with a total ESD protection system.
Download White Paper (PDF Reader Required)

05 Dec

Ben-Top Ionizer and decay time vs. effective distance

Q: I have one question/problem that I would like to ask regarding an experiment to test a bench top air ionizer. From the attached documents, there are 2 graphs of decay time versus effective distance, one for decay time on negative charges and the other one for decay time on positive charges. As you can see, the closer the bench top air ionizer (effective distance), the lesser the decay time will be. My question is, why is it during the distance of 20 to 24 inch the graph line become a straight line (saturated) and not growing linearly like the other points?

A: I see you’re using the Bench Top style air ionizer. The “PC” means that it is “targeted” coverage as opposed to “extended” coverage. The posted operating range appears to be from 1′ x 5′ or 12″ to 60″.

Your graphs range in distance from 4″ to 32″. I’d consider using a test method recommended by EOS/ESD S3.1 if you haven’t already.

Was your humidity really at 80%?

This ionizer also has a heater function. I’m not familiar with that particular feature, whether or not it is a factor here.

Ionizers have two properties that ANSI EOS/ESD S3.1-2000 defines through the use of a CPM; discharge time and offset voltage.

Ionizers increase the electrical conductivity of air, which is especially useful in environments that use insulators which cannot be removed from the EPA (such as PC boards). Grounding an insulator doesn’t remove it’s electrostatic charge. They also reduce the effect of the earth’s field, which increases with the altitude above the work surface of the DUT(device under test).

Now things get complicated.
Discharge time:
Ionizers decrease the charge on the CPM exponentially with the time constant RC.
R = resistance of air (Keep in mind that air resistance increases with the distance that ions must travel).
C = capacitance of the plate. ( Keep in mind that smaller objects have lower capacitance and the time to discharge them maybe shorter than the discharge time).

Offset Voltage:
This deals with induced potential on objects. It has been found that the mobility of negative and positive ions are different. Thus, there is a small electric field generated which is zero at the work bench surface (if dissipative ESD mats are being used) and largest as you get closer to the ionizer. We use an isolated system, which reduce this effect by a simple law of nature- charge cannot be created or destroyed in an isolated system. With the more sensitive devices, such as an MR head on a disk-drive, I’d be very careful here as no system is perfect. Will electrical potential damage a device, or will the rate of current discharge do the damage?

Unfortunately, there’s other things involved with your chart, such as the mere dimensions of your plates and the distance from them. Really close to the plates, the effects of decay time are linear and are affected by a plane source. Further out to some point, you may be dealing with a line source which drops off as the function of L/2 where L = length from the plate, and ultimately, when you get 7 times that length or 7L, you are dealing with an inverse square or L / 4 equation- or point source- out there you are parallel to the source or detector. An example of this equation is to calculate the surface area of a sphere with a diameter of 2 units as opposed to one with a diameter of 4 units. Suffice to say, nature is too complicated to be linear.

I’ve only scratched the surface on your question here and I’d like to give it more thought. I’d run the experiment myself here, but I currently have some equipment in for calibration. For now, let’s move in the direction of testing per EOS/ESD S3.1.

05 Dec

Which is best: Epoxy or Vinyl and Conductive or Dissipative?

Q: We are removing old vinyl tile and replacing with ESD protective tile. We are wondering if ESD conductive or dissipative is best. Our business is dehydration baking, final functional testing and packaging semiconductor IC’s with design circuits typically in .25 micron range. We need recommendations on conductive vs. dissipative and epoxy vs vinyl tile. The area is not high traffic. Thanks.

A: Good questions. In selecting an electrical range there are several key factors to consider, these are in order of importance in our professional opinion:

  1. Device sensitivity?
  2. Does the type of work being performed in the protected area include, working with Power Supplies?
  3. Is your staff going to be wearing personnel grounding protection?
  4. Are there any environmental conditions to consider?
  5. How important is meeting industry standards to you and your company? e.g.
    • EOS/ESD S7.1
    • ANSI/ESD S20.20
    • ISO Compliance
    • In-House Standards
    • Customer Contract Standards

Based on what you have described in you e-mail, conductive range is best suited for your application, dissipative should not be considered. See the attached white paper on this specific subject. As this particular document has even been published yet, please keep this document confidential for your internal use only.

The factors that should be considered in choosing a Material Type are as follows:

  1. What is the intended use for the floor? What type traffic will the floor see? Will liquids or spills be anticipated or utilized in this area? Do you own or lease the building? Will odors be a problem during the installation process? Are you fully operational and or will the work be done in phases? Budgetary factors Performance warranty Maintenance level expectations
  2. Esthetics

I think this will give you some things to consider moving forward. Please see the attached floor comparisons chart for additional things you should consider, this chart may prove helpful to you and your team. Let us know if we can provide you with flooring sample submittals, product specification sheets, quotations, etc. I would like to talk to you in greater detail regarding Epoxy vs. Tile, we have many millions of square feet of experience in this category, so please call me when you have some time.

Please let us know how we can better support you and your company moving forward, as your satisfaction is our highest priority!
See also: ESD Open Forum(PDF); ESD Flooring Comparison Chart(PDF)