Anti-static wrist band for in-house PCB assembly?

[Martin F]

Hi all,

We're doing some light PCB finalization in our office and we're having some challenges/risks related to static shocks.

We were thinking if there's an anti-static wrist band we could use during production.

Does anyone have experiences with using these - and whether there are specific types that work better than others?
E.g. how to handle the grounding in practice in-doors?

Looking forward to your thoughts,
Martin

[helius]

ESD control is a very broad topic, and there are many books written on the subject.
Any static discharges that a person can feel as a "shock" are far into the danger area for CMOS components. Even insensible discharges can kill chips, especially prior to soldering. Wrist straps are one component of an ESD solution, but don't neglect ESD work pads, ESD component boxes and bags, shoe straps and/or floor treatments if components need to be carried from one workstation to another. ESD monitors are also recommended to provide quick feedback for any failures in the protective devices.
Also consider humidification if your work area is dangerously low in relative humidity, below 20-30%RH.

Simply as a starting point, which may or may not be enough in your particular situation, you can wear a 3M or other major brand (ACL, Desco) wrist strap and clip it to the ground lug of your soldering station. This would be about the minimum protection to consider.

[coppercone2]

I always wondered how carts with casters perform ESD wise. Do they generate when you roll it around? Like if you need to get circuit boards from one area to another and you load them up on a cart. Is it a extra hazard, especially with a metal cart that has plastic wheels? Especially with plastic/synthetic tile floors  that are super common in factories, or epoxy concrete liner. I noticed someone I know that has linoleum floors seemed to always have fucked up electronics for some reason, whereas I never had real problems. I have very heavily worn wooden floors that don't really have laquer on them anymore and I like to wear cotton and leather everything I can.

I always wondered if something like a untreated iron-wood floor would be a good candidate for a electronics lab. It should hold up pretty good. The aussies should not have a problem with that 

I figure untreated wood would work well since its used in ball mills for black powder manufacturing IIRC. Just needs to be fucking hard so you don't get too many splinters.. but all those SMD parts should make you proficent in removing them

[SeanB]

Cart with wheels simplest solution is to bolt a short length of chain to the metal frame, so it drags on the floor.  Generally you use a small diameter welded link chain, with a 10mm gap, and use 5 links, and use the fixed wheel bolt to hold it so the one link drags across the floor. This dumps the static charge.

As to the rest of the area, if you have vinyl floors change your floor cleaning solution to an antistatic one, or simply start washing the floor with liquid fabric softener in the rinse water. Carpet grab a wet extractor and use the fabric softener ( generally a capful in 10l of warm water is about right) in the tank, and do all the carpets. Also works on vinyl to give it a clean.

On the work areas grab the ESD matting Dave has in his work areas, and place on the benches. there is a thread about it here with ordering info for the EU IIRC. Then get the anti static wristbands, a connector kit for the wristbands to connect them to ground ( either a dedicated ground rod outside, or some grounded frame of the building or cold water piping that is grounded properly and not in plastic piping) but as OP is in a country with TT supply I would avoid mains earth unless you know for sure the ground system is in good order.

Then operators should wear static dissipative footwear, cotton clothing ( not polyester or wool) and coats which are laundered with fabric softener liquid.

[coppercone2]

do you think ironwood would be a good choice for a lab floor?

and are cart's particularly bad? I know you can ground em but I mean just like, is it a big hazard?

[SMTech]

At the very least you should put mats on your benches and wear grounded wrist straps & this is very cheap to do.
However if its a proper lab it could be best to go the whole hog, with anti-static flooring (this can be paint or matting), a footstrap/shoes & double up with a wrist strap when its not too annoying. ESD lab coats can't hurt either, all depends how much you want to mitigate the risk.
 Proper ESD benches will have plenty of grounding studs and mount points on them to attach your straps and earthing points to and have the bonus of having a bunch of accessories relevant to electronics labs & assembly lines. Like these https://www.staticsafe.co.uk/products/esd-workbenches-chairs/esd-workbenches-kitehawke/kitehawke-esd-accessories/ in our facility we use Technibench.
Operators (ESD) chairs are all on castors and they have a grounding chain.
https://www.bondline.co.uk/ESD-Sprays-and-Cleaning/KillStat-Sprays-And-Cleaners/KILLSTAT-Anti-Static-Spray/KSS32 you can also treat surfaces with something like this to reduce the risk of static build up, don't forget this is basically what has been done to pink/blue anti-static bags, they don't protect, they prevent.

[IconicPCB]

I use wrist strap and dissipative work area matting.
In the floor i regularly spray a bit of fabric softener solution.
Humidity is Your friend. 

I am contemplating getting some ultrasonic humidifiers into the air conditioned space.

[Martin F]

Hi all,

Do you have suggested tools for measuring whether our ESD setup is "good to go" for production?
E.g. for measuring that the wristband/mats have the correct resistance (via a simple LED, visual or similar) or in other ways "checking" if an operator can start producing? We're looking for something basic/low cost for now, but if you have suggestions let me know.

Best,
Martin

[Gribo]

You should have 1M to ~100M Ohms resistance for the wristband. There are ESD checkers where the operator puts the wristband or heel strap, presses a button and a Go/No go indicator lights up. Example: https://canada.newark.com/scs/725/wrist-strap-monitor-9v/dp/83F8475?CMP=KNC-BCN-GEN-KWL&mckv=|pcrid|{creative}|&msclkid=3dd96000c2da1247a2ec3c06412cccbf

[SMTech]

Humidity is Your friend. 

Well it is and it isn't, its your friend against static and your enemy against shelf life, surface mount components and some sensors.

[nick liu]

Using an anti-static wristband during PCB production is a good practice to minimize the risks of static shocks and protect sensitive electronic components. Here are some considerations and recommendations for using anti-static wristbands:

1. Importance of Grounding: The primary purpose of an anti-static wristband is to provide a path to ground any static charges on your body. Proper grounding is essential to ensure effective static discharge. The wristband should be connected to a reliable grounding point to redirect any accumulated static charges away from you and the PCB.

2. Types of Anti-Static Wristbands: There are two common types of anti-static wristbands: adjustable fabric wristbands and disposable wristbands with built-in grounding. Adjustable fabric wristbands are more popular as they are reusable and can be adjusted to fit different wrist sizes. They typically have a metal plate or clip that connects to a grounding cord. Disposable wristbands are convenient but need to be replaced after use.

3. Grounding in Practice: To achieve proper grounding indoors, it is essential to connect the wristband to a reliable grounding source. A common approach is to connect the wristband's metal plate or clip to a dedicated grounding point, such as a grounded ESD (Electrostatic Discharge) mat or a verified grounding point on a workstation. Ensure that the grounding point itself is properly connected to a reliable earth ground.

4. ESD-Safe Workstation: Creating an ESD-safe workstation is crucial. Apart from using an anti-static wristband, consider using an ESD mat on your work surface. The mat should be properly grounded, and all components and tools on the workstation should be ESD-safe. Use ESD-safe containers and handling equipment to minimize static risks.

5. Training and Compliance: Ensure that all personnel involved in PCB production are trained in ESD precautions and understand the proper usage of anti-static wristbands. Following ESD guidelines and industry standards, such as ANSI/ESD S20.20, helps maintain a controlled ESD-safe environment.

[Feynman]

The fundamental idea of ESD control is to have everything at the same potential as much as possible, so it's impossible for discharge events to occur. And if there are potential differences, they should be evened out slowly to not cause any harm. An ESD event is evening out potential differences, too, of course. But way to fast and thus harmful.

I would consider a wrist strap and a ESD mat as the bare minimum. Both need to be connected to a common reference potential. In most situations the (protective) earth of your outlet is the most convenient one. There are special ESD wall adapters that also include the 1 MOhm safety resistor. You can connect both your wrist strap and your mat to that wall adapter. Often times you can connect the wrist strap to the mat instead.

Depending on your circumstances, this might already be the Pareto-80%. Just try to keep your ESD sensitive devices in an ESD safe packaging (e. g. shielding bags) when you are not working with them.

There are no specific types for either mats or wrist straps. Most work more or less the same. Just choose a reputable supplier and maybe make sure the manufacturer claims conformity to an ESD standard (EN 61340-5-1 is a popular one).

Just don't fall for the wireless wrist straps you find on amazon 

Do you have suggested tools for measuring whether our ESD setup is "good to go" for production?

There are special ESD testing stations where you can test ESD shoes and also wrist straps. As the maximum wrist strap resistance to the reference potential is 5 MOhm (at least according to EN 61340-5-1) most DMMs should work, too. More precisely, the point you are connecting your wrist strap to should have more than 5 MOhm to the reference potential. Strictly speaking you need to test both the connection point for your wrist strap and the wrist strap plus the cord itself.

The surface resistance of ESD mats is usually way higher than 5 MOhm, so you are out of luck with most DMMs.

But there are fairly cheap high resistance meters especially for ESD verification, e. g. this one. For an at least somewhat standard compliant measurement you probably need also a probe like this one. With those two devices you can measure the resistance of your ESD mat's surface to your reference potential easily.

[TimFox]

Wireless:  see  https://sma.nasa.gov/news/articles/newsitem/2018/01/10/esd-wireless-wrist-straps-the-shocking-truth  for NASA's view on these silly things.