Is my ESD safety procedure sufficient?

Question

I will soon be assembling multiple computers and want to reduce the danger of ESD as much as possible. Not an expert myself so I'm looking for people with knowledge in ESD safety to comment on my planned procedure.

The ESD tools I will buy is an antistatic wrist wrap and an antistatic mat. The surface of my table is melamine laminate so I think the mat is required.

The most common advice I have seen is to install the PSU into the cabinet, connecting power cord to wall socket while turned off and attaching antistatic wrist wrap to cabinet. However, this will not have any effect in my case as the systems I'm building are using picoPSUs with external 12V power bricks and these have no ground wire.

The following are the steps I will follow while assembling a computer:

1. Attach antistatic mat and wrist wrap to cabinet.
2. Put on wrist wrap.
3. Place screwdriver and other tools on mat.
4. Unpack motherboard from ESD bag and place it on mat.
5. Mount CPU, CPU cooler and M.2 SSD on motherboard.
6. Install motherboard in cabinet.
7. Install RAM and picoPSU.

The flooring is linoleum or vinyl and I will be assembling the computers barefoot while sitting on a wooden stool.

Is the above enough to reduce the risk of component damage from ESD, or is the procedure completely wrong?

Answer 1

ESD is not just prevention from becoming ungrounded. ESD events are most destructive when there is a low resistance path to follow. The mats and straps have resistance in them to prevent a sudden discharge path when the hands touch other objects or when new components are brought into the work area.

The bare feet would be exactly wrong. As you stand up and sit down on the stool, for example, you will now have a path for rapid discharge to the floor and secondary current flow can be rather chaotic. Also, the bare feet make for a path for dangerous electric current in fault conditions through your body. Really, the stool should be ESD coated and you should wear an ESD smock so that your natural movements on the stool don't become an electrostatic generator.

Keep the tabletop + computer + human as close together as possible ... electrically speaking. The straps and mats do this. Keep that work group as far from other unprotected objects as possible. 1 meter is a typical figure given for distance through air that friends, dogs, file cabinets and the like must be kept away.

Don't plug anything into mains any time during the assembly. First it is dangerous due to mains coming too close to the human; and secondly, it provides a path for rapid conductivity. The most standard approach is to connect the mat to building earth. For this, you will have to find plumbing or other metal that gets into the ground beneath the building. No, you can't use the ground lug of the wall outlet, that has horrible inductance to real earth and there are cases where it has been mis-wired by the original contractors.

At all times, consider your personal safety above the safety of the equipment.

Answer 2

Is the above enough to reduce the risk of component damage from ESD, or is the procedure completely wrong?

The idea behind ESD protection is to minimize the potentials of all surfaces to zero. There are two problems:

1. Having a surface or object charge, usually due to friction (triboelectric charging) and then discharging the built up charge into a circuit.

2. Having a material build up a charge and cause an electric field. This electric field then destroys circuits as it passes near them and induces a charge.

The first one can be mitigated by first and foremost wearing an ESD strap between you and the device being serviced. That way if you build up a charge it will be dissipated through the strap. The second thing you can do is put all materials on a mat that is conductive and also connected via a conductor to the device being serviced.

To protect against the second problem, you need to make sure no materials can build up a charge, or that the charge is blocked. ESD tools are available as plastics can build up a charge on their surfaces. An ESD lab coat could also block electric fields from clothing (clothes are great ESD generators). Wood also generates a charge so its not the best ESD material. However, ESD protection must be balanced with cost. In industries (Aerospace and Medical) where failure is costly, the cost of full ESD protection is worth not having failures. There are e monitoring devices and standards to make sure equipment (and people) are fully grounded. In many other industries it's not worth the cost in time or equipment.

If I were a computer tech, I think a wrist strap and an ESD mat would be sufficient. If its a service call to a data center with an expensive flight involved, or a critical server failure is costly, I would consider wearing a lab coat and using ESD tools.

Answer 3

ESD protection, it's a black art!

:)

The single most important number: the RH humidity in your room. High humidity removes all the ESD hazard. So measure it. Get one of those little tempr/humidity meters.

Or cheaper: rub an inflated balloon on your head or arm. If it raises hair and feels "static-y," then the RH in your room is far too low, and if you walk across a nylon carpet, you'll end up with a few kilovolts on your body.

So, if you're in Wisconsin winter with 5% RH, then even extreme ESD protection might not be enough. Fingertips rubbing on metal objects will charge them up! But if you're here in Seattle with 95% RH, all the high-voltage surface-charging gets shorted out by the gigohms of surface conductivity. In that case usually little protection is needed (although a grounded wrist-strap might be a good idea anyway.)

Rather than guessing about ESD sources, instead make or buy an "electrostatic locator" and wave it all around your room and workbench. Search out all your major sources of high-volt surface charges. Here's one for $1 which senses single volts, or detects kilovolts from meters distance. With a Locator you can prove to yourself that no kilovolts are hiding on your body or workbench, or anywhere in your room.

INCREASE YOUR HUMIDITY. Perhaps run a hot shower with bathroom door open, until RH reading in workshop is well above 70%, so a rubbed-balloon cannot raise arm-hair, even slightly. (Use your one-dollar locator-FET to verify the lack of charging.)

If humidity must remain low for some reason, and your workbench surface gets charged from arm-rubbing, use a wood desk instead. If plastic chair is making voltage, get rid of it, use a wood stool.

ESD isn't so weird if you can "see" all the e-fields using that little LED-device. Mystery removed.