Apparel – Ground Zero Electrostatics Blog

Building an Electrostatic Protected Area (EPA)

Almost everyone’s familiar with the image of a white “cleanroom” or “bunny suit.” They show up in just about every depiction of people working in computer facilities in popular entertainment, and it’s a highly sought after specialty ‘armor’ in the video game Fallout 4.

What most people may not know is that the suits are designed not to protect the person inside, but the delicate circuitry they’re working on. But not everyone who works with small, sensitive electronics needs to spend money for a full-on, disposable suit.

If you work with a lot of small electronics, a more affordable solution is to put together an electrostatic protected area (or EPA). This doesn’t have to take up a lot of space and can actually be quite portable. It just needs to be done properly.

Let’s start with the basics and work our way up to the safest and most expensive options.

Simple EPA

At a bare minimum, all personnel working within an EPA should have a personal grounding wrist strap. These make sure any excess energy is grounded – forced away – from the electronic devices and circuit boards being handled.

Connected to that grounding strap is a dissipative mat. Dissipative means quite simply to disperse or disappear. A properly designed and implemented dissipative mat does for the surface what the grounding wrist strap does for the person – protects sensitive electronics from electrical discharges.

Mats can be purchased pre-cut or in rolls, depending on what your needs are.

Attached to both of these is a common point cord, also referred to as a grounding cord. These cords are fully insulated and take any electrostatic charges away from the person and the ESD mat to be grounded safely.

Often these simple options are packaged together as a field service or workstation kit that can be purchased as one unit to avoid forgetting any key elements.

Now that we’ve established the minimum requirements for an EPA, let’s look at additional options that can be easily implemented within your system to further insure the safety of the components and reduce the risk and excess cost of replacement.

From the Ground Up

For more permanent EPA installations, there are a variety of flooring options that can be integrated. Everything from conductive and dissipative vinyl tiles to anti-static carpeting that can be utilized in the work area or just in the area surrounding your EPA system. You can even add flooring with a high-end moisture barrier as well as anti-static protection.

Sole Protection

One of the most obvious ways we build up a potentially dangerous electrostatic discharge is just by walking. Static charges build up naturally. While a personal grounding wrist strap will help dissipate the charge, there are additional options for your feet.

Shoe covers with conductive strips are a quick, low cost addition to an existing EPA system and great for alleviating the risk of allowing visitors into the EPA area.

For employees whose duties mean they spend substantial time in the EPA area, you can add foot and heel grounders, toe grounders and sole grounders.

For even more protection, grounders can be upgraded to ESD shoes. These come in a variety of styles for your business setting – even weatherproof boots and hiking models.

Additional Considerations

Adding isolation protocols and ESD protective containers can also complement your EPA system and reduce the chance of any accidental charges building up or discharging into your electronic components.

Of course grounding should be a consideration with any additions to your EPA system. Whether it’s flooring or matting, grounding cords with a built in resistor add that much more protection to your area. And the more working parts you have, the more grounding capability you require.

There are simple options to increase the grounding ability of any size EPA system, as well as monitors that can be added to the system – at the personal or system-wide level.

And if you really feel the need to cover yourself top to bottom, there are more workable clothing options as well.

How do we test ESD conductive or dissipative gloves?

Q: How do we test ESD conductive or dissipative gloves?

A: The glove industry offers gloves for the protection of ESD sensitive items by using materials that will provide specific measurable “intrinsic electrical resistance of gloves and finger cots” as per ANSI/ESD SP15.1-2005.

Some materials are being used which reduce the amount of charge generation “and/or have static dissipative properties to reduce charge accumulation”, such as Nitrile or vinyl. I would image cotton could be effective based on the layer of sweat on our skin. But if you require ESD gloves in the Static Conductive range, those would need to be specifically made for that purpose. I’m currently working on nailing down an exact value of what these gloves should read and how that affects the ESD testing of it and the closest I could find comes from a test fixture from Prostat called the CAFÉ, or Constant Area & Force Electrode. They recommend using 1.5 to 10 volts when the measurement of glove in combination with personnel through a wrist strap assembly without the 1 meg Ω resistor is less than 1 meg ohm. They use 10 volts between 1.0E6 Ω and 1.0E7 Ω. Then they use 100 volts for above that. This is fairly easy to do using a sophisticated megger like the 801 in manual mode, otherwise the mere testing of the glove per 15.1 could be a challenge.

Here’s what confuses about ANSI/ESD S20.20-2007 and -1999 …

What’s the range of the glove and finger cots? Only in 20.20-2007 Tables 1, 2, and 3 final column does it give us “Required Limits” to measure up against. So then what? Go to manufacturing specs. Some list a value, some don’t. Be careful how they’re categorized; anti-static (describes that it’s low charging but doesn’t really quantify a resistance range unless you’re talking about packaging), static dissipative (1.0E6 Ω to 1.0E9 Ω ??), and static conductive (less than 1.0E6 Ω but greater than what?? 1.0E4 Ω rings a bell, but I’d hope it’s not less than that.).

Ok, so for our Static Conductive or black finger cots, they measure between 1.0E6 Ω and 1.0E8 Ω per ASTM D257 and meet the static decay specs per MIL-STD-81705B from 5000 to less than 100 volts in less than 0.01 seconds.

So here’s the upshot; My improvisation in measuring ESD gloves and finger cots involves using the PFA-861-H Handle (see attached), a DUT (esd glove), and a wrist strap without the 1 meg ohm resistor for measurements known to be below about 1.0E7 Ω , I hook that up to my meg ohmmeter and see what I get (see attached photos).

wand wand-and-sd-glove wand-and-sc-glove

This ESD TR20.20-Handbook has a wealth, a plethora of information about ESD gloves and finger cots, such as referring to yet other standards such as ANSI/ESD STM11.11 Surface Resistance Measurement of Static Dissipative Planar Material , and let’s not forget ANSI/ESD STM11.12 Volume Resistance Measurement of Static Dissipative Planar Materials, oh, and of course ANSI/ESD STM11.13 Two-Point Resistance Measurement of Static Dissipative and Insulative (what the??) Material, then it goes on to tell us to use the CAFÉ method, which is specifically designed for resistance measurements at the thumb and fingertips, which can yield much lower results than those obtained by the above test BECAUSE THEY INVOLVE A REAL LIVE PERSON, THE WAY THEY ARE ACTUALLY USED IN PRACTICE! Oh, and they say you can only measure once due to a “person’s skin emissions”. Fair enough. Time to reorder?

So… If this info helps anybody, let me know and send over a comment.