05 Dec

The difference between Low Static and Static Dissipative

Q: What is the difference between Low static 3.5kv carpeting and static dissipative carpeting? When used on walls is 3.5kv carpeting ok in electronic equipment rooms?

A: When people refer to 3.5 kV carpeting I believe they are referring to the threshold voltage that people can feel as a nuisance static shock. We deal primarily with manufacture, test, assembly, and application environments where the end-user is protecting expensive electronic components, explosives, assemblies, etc. and the threshold for their needs is down to 100 volts and less.

I believe the 3.5 kV carpeting is considered to be somewhat antistatic (resists or has reduced tribocharging abilities) and is treated topically with some temporary chemical. These types of carpet do not satisfy our needs to provide long-term solutions for the commercial, industrial, and even consumer electronics industry.

I’d like to find out more about what you’re using the carpet for. Are you using it on the walls to deaden noise or create some special environment for audio design? If you need some kind of ESD protection, can you find out what your voltage threshold is- or what is the highest acceptable voltage that your environment can tolerate?

We offer ESD carpet in broadloom form and in tile form in both static conductive (typically around 2.5e04 or 25,000 ohms to 1e06 or 1 Meg Ohm) and static dissipative (1E06 – 1E09 ohm). As the resistance increases, the generated charge dissipates less rapidly to the point that a charge potential exists somewhere in the system and an ESD event occurs. This ESD event may occur without the end user knowing, but it may damage or destroy sensitive devices. Having a textile with a resistance in the static conductive range will discharge this charge potential more rapidly and work to prevent a charge from getting too high in the first place. Different textiles tribocharge at different rates and increase to different potentials, depending which textiles are making contact with and separating from them. Many carpets perform fairly well compared to other textiles in a humid environment. The humid environment may knock the created voltage down from 10’s of thousands of volts to thousands or hundreds of volts, but not low enough to prevent ESD Sensitive Devices from getting damaged or destroyed.

I hope I’ve touched on some of your questions but need to know more about your current application to help you better.

05 Dec

ESD Compliance: Test the ESD Devices, and test the testers

Q: How does a wrist bandcum footwear ground tester differ from the work station monitor? Can we not use only the work station monitor when it can monitor the worthiness of wrist strap even? And, Can we not check the worthiness of a wrist strap with a normal multimeter

A: I think that I understand your question here.  One way or another, a company needs to say what they are going to do in terms of ESD compliance.  They need to then do what they say they will do and document it.  They need to test the ESD devices.  They then need to test the testers.  And they need to show records of such in a pass/fail document and to prove that they are committed to quality and do not accept anything into the environment than will lead to a failure.

A wrist strap/footwear tester is proven and tested.  It is convenient to monitor and record the compliance to a whole shift of people in a given EPA.  But what if someone tests their wrist strap that morning and it fails at 10:25 that morning.  They won’t know it failed until later that day. 

The advantage of the constant monitor is that it not only alarms the moment it fails but it also forces the user to keep it on (wrist strap) while seated at the ESD workstation.  That’s fine.  But you need to test the testers periodically.  And to document those tests.  I hope I understood your question and answered it accordingly.

I suppose you could check the worthiness of a wrist strap with a normal multimeter.  I have a device that measures the connection from a connected 4mm, 7mm, or 10mm snap, through the coil cord and 1M Ω resistor, and two conductive cylinders that measure a stretched out wrist strap.  With it, I can measure the cuff only, the cuff and cord, or the cord only.  It cost me (us) a small fortune.  I have a Fluke 123 Industrial Scopemeter and a Fluke 77.  They are great meters, up to about 40M Ω or 4.0E7.  If you have wrist straps that are conductive enough, then great.  Good luck.  You may need a Megohmmer.

05 Dec

ESDA Specifications

Q: May I know the standard test procedures and parameters (ie: surface resistivity/surface to or person to ground resistance, decay time or any other parameter if applicable) and recommended values for confirming the worthiness of the following ESD items?

  1. ALL ESD PACKAGING ITEM
  2. ESD FLOOR AND WORK SURFACES
  3. ESD CLOTHINGS
  4. ESD FOOT WEARS
  5. ESD HANDLING ITEM viz., BRUSHES / BINS / PCB RACKS

A: Please consult your copy of ANSI/ESD S20.20-1999 from the ESDA at http://www.esda.org/.  It has specific documents for different technical elements.  For example, S1.1 for wrist straps, 2.1 for garments, 3.2 for ionization, 4.1 for worksurfaces-resistive characterization, 4.2 for worksurfaces- charge dissipation, 5.1 for Human Body Model, 5.2 for Machine Model, 5.3 for Charged Device Model, 6.1 for grounding, 7.1 for resistive characterization of materials-flooring materials, 8.1 for symbols-ESD awareness, 9.1 for footwear-resistive characterization, 10.1 automated handling, s11.11 surface resistance of static dissipative planar materials, 11.12 for EDS items-volume resistance of…, 11.2 for Triboelectric charge accumulation testing, 11.31 for bags, 12.1 for seating, 13.1 for electrical potential from soldering/desoldering hand tools, STM 97.1 for floor materials and footwear-resistance measurement in combination with a person, and STM 97.2 for floor materials and footwear-voltage measurement on a person just to name a few.

I could spend a lot of time digging up actual values for these specific items that we provide, but I haven’t put anything like that together all in one place.  I will work on that and perhaps we can post that info all in one place.  But keep in mind.  We do not determine the parameters, we merely work to comply with them.

05 Dec

People are a great generator of static electricity

Q: How does ESD Gloves, Aprons and Bunny Suit help for static discharge? WIll it not be mandatory to wear the wrist band, footwear and heel strap along with it?

A: People are a great generator of static electricity, among other things. The ESD gloves, aprons, etc. enable you to work and interface with sensitive components and equipment while protecting them from an ESD event as well as other things like contamination from human skin, street clothes, dirt, dust, etc. It will be mandatory for personnel ground to wear a wrist strap when in seated operations in a manufacturing environment or in the field. For personnel ground in an environment where you are standing or walking about, you do NOT have to wear a wrist strap if you have sufficient ESD footwear in conjunction with an ESD flooring system. The above requirements are per ANSI/ESD S20.20-1999 Table 1.

05 Dec

ESD Garments in addition to Wrist Straps and Footwear/Grounders

Q: Is it necessary to use the ESD garments? Is it not possible to ground the charges developed through a person’s clothing through the human body which is grounded through a wrist strap, footwear or heel strap while working at an EPA?

A: This depends who’s in charge.  If the ESD manager wants to require ESD personnel clothing and redundancy of ESD compliance for improved ESD control, they are the one to determine that.  More and more I’m seeing the use of ESD smocks outside of the cleanroom environment.  The company and their clients are reaping the benefits of increased quality control and reduced “out of box failures”.  Cloth is proven to be a better conductor of ESD charges than some types of clothing, but not everybody wears cotton.  Some people have dry skin and the ESD garments are a good idea for added protection and a requirement in some environments.

I’d like to add that when seated in an EPA, you must have your wrist strap on regardless of ESD Garments, ESD footwear, ESD flooring system, etc.  That’s a requirement of ANSI/ESD S20.20-2007 page 4 section 8.2 Personnel Grounding; “When personnel are seated at ESD protective workstations, they shall be connected to the grounding/equipotential bonding system via a wrist strap system.”

Further, per Table 2 note 2, “For situations where an ESD garment is used as part of the wrist strap grounding path, the total system resistance including the person, garment and grounding cord shall be less than 3.5E7 ohms.”

05 Dec

Using an ESD Chair when already protected

Q: Is it necessary to use an ESD Chair when the humany body is already grounded through a Wrist Strap, Footwear or Heel Strap when working in an EPA?

A: I think it’s a great idea.  I can be sitting at a workstation with an ESD flooring system, have a wrist strap on and when I get out of my chair, not generate more than 50 volts.  I may not generate more than 5 volts.  But what if I take my wrist strap off and jump out of my chair?  I can easily generate 100’s of volts.  Oh, by the way, jumping should not be allowed in an EPA.  If you have great ESD shoes or sole grounders and you keep at least one foot firmly planted on the ground at all times, then maybe your ESD chair is redundant, but still an added piece to the chain in your EPA system.

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.