2
\$\begingroup\$

I am a manufacturing engineer for a company that just inherited a large electrical build. I am struggling to find ESD information for multiple workbenches. This is my last resort so I am hoping you can help.

Currently we have the ESD workbenches daisy chained and grounded to the ceiling or metal structural beam on the manufacturing floor at 1 point. I have read they should not be daisy chained. We have about 10 workbenches next to each other. How would I ground them all without them being connected with a ton of wires?

We have ESD mats sitting on top of the workbenches. The manufacturer says the mat should be grounded just from being on top of a grounded workbench. Is this accurate? If not, I do not have a standard outlet with center screw that I could use as ground. Each bench has essentially a powerstrip built in. Can I use that to ground the mat if the bench is grounded? We use ESD wrist bands that are snapped onto the worksurface mats.

Under the benches we have ESD floor that is puzzle piece tile style. I believe this is connected to 1 work bench at 1 point with a grounding cord. Is that enough for all 10 benches?

Finally, how can I verify the entire system is properly grounded? I have seen multimeters, which we have, but then I read that does not work. I have seen 5 lb probes with resistance meters, I have seen ohm meters. All of the info and videos I watch they attach it directly to the outlet but that isn't possible for this situation since we aren't grounded to an outlet.

\$\endgroup\$
4
  • \$\begingroup\$ Proper ESD resistance is 10~12MegΩ. You need the 5lb type resistance meter to measure it properly. And yeah, it sounds like you're going to need more wires. But without a drawing of some sort that's a guess. \$\endgroup\$
    – Aaron
    Commented Mar 5 at 20:53
  • \$\begingroup\$ A good compromise would be to connect the 1st and the 10th benches to earth, or the 1st, the 5th and the 10th. Also use two separate earthing points. To check if it's properly grounded, pull a wire between the main earth terminal and one probe of the multimeter. Put the other probe on the surface to be tested. \$\endgroup\$
    – Fredled
    Commented Mar 5 at 21:47
  • \$\begingroup\$ @aaron jensentools.com/product/… Can you tell me if this will work or if I need to get the more expensive analog model? \$\endgroup\$
    – MDD
    Commented Mar 5 at 21:57
  • \$\begingroup\$ I recommend listening to the Pick, Place Podcast | How to Protect PCBs from ESD Damage, it's basically Sparky256's answer, but longer. \$\endgroup\$
    – Jeroen3
    Commented Mar 6 at 6:52

2 Answers 2

Reset to default
3
\$\begingroup\$

At the manufacturing plant I worked in it was up to me to implement anti-static procedures and protocols. First all parts bins (stock room and production floor) were replaced with anti-static types.

14 ga stranded green wire was daisy-chained from bench to bench then bonded to a ground bar at a service entrance panel. What makes it safe is that ALL wrist and ankle straps had a built-in 1 megohm to 10 megohm resistor to limit shock current to 200 microamps max, while still preventing static build-up.

Having done all of this UL still required a once-per-year ohm test of each strap, as well as solder iron tips. Over years straps wore out and had to be replaced.

Over my remaining ten years the daisy-chained grounding had no issues, but anti-static training became an issue, as newer LEDs and certain ICs needed to be handled with special gloves and/or very clean hands.

No food was allowed as many snacks can be salty and greasy, thus contaminating wires and component leads and leading to corrosion within a week.

Anti-static/anti-corrosion procedures are a mix of many steps and protocols that need to be learned by those who handle static sensitive parts. A good earth ground is just a starting point.

I should add that you will need to have the production and stockroom floors painted with anti-static enamel. We found that a medium or steel gray did not offend anyone or cause glare from bright fluorescent tube lights.

If budget allows consider professional test stations for the wrist and ankle straps, as they make this step quick, and it can be done daily.

I would say that any meter that can read ohms to 10 megohm will do, but UL may require a accuracy of 0.1%, as they did where I worked.

NOTE: The grounding wire that connects bench to bench (workstation) should be bare copper under the front lip of each bench so when someone sits down they connect the alligator clip of their wrist strap to this wire right away.

This way they are grounded at the wrist and ankle. If they solder static sensitive parts then their soldering iron tip needs to be grounded. UL and ISO may insist on temperature-controlled irons with digital readout. Another sticky issue is lead-free solder, I.E. Rohs compliance.

Once your compliant UL and ISO will give you rolls of holographic stickers that will allow you to ship qualified products to most any country.

\$\endgroup\$
5
  • \$\begingroup\$ lol yeah. It's never the workstations. It's always the bins! \$\endgroup\$
    – DKNguyen
    Commented Mar 6 at 1:08
  • \$\begingroup\$ @sparky256 thank you, this is very helpful!! \$\endgroup\$
    – MDD
    Commented Mar 6 at 13:06
  • \$\begingroup\$ Were chairs a concern? I'm at a co that's involved with a rapidly growing and kindof out of control manufacturing operation due to a merger, and the assy floor seem to be starting from a very informal level of control \$\endgroup\$
    – Pete W
    Commented Mar 8 at 0:42
  • 1
    \$\begingroup\$ @PeteW Not such an issue if ankle straps in use with anti-static floor paint. Chairs would likely have metal legs, which can have metal feet, but main no-no would be wood or carpeted floors. Remember that floor is grounded with 8 - 14 ga wire bolted to floor and goes to ground block at a service panel. \$\endgroup\$
    – Sparky256
    Commented Mar 8 at 3:20
  • \$\begingroup\$ @Sparky256 - thanks. I was asking for our own use. Epoxy floors, facility which traditionally did mechanical and glass. Furniture is mix of what look like nice anti-static workstation chairs with chain, and plastic fantastic from Staples or some such \$\endgroup\$
    – Pete W
    Commented Mar 8 at 16:18
1
\$\begingroup\$

Static control in manufacturing environment is a big topic. You have the beginning - benches, wrist straps. Heel straps and moisture control (not too dry, not too wet) are also recommended. There are ESD test stations that can check your straps, if they are above or below certain resistance thresholds, you should replace the straps. Example: https://transforming-technologies.com/product/gts900-esd-wrist-strap-and-footwear-testering-station/

\$\endgroup\$
1
  • \$\begingroup\$ Thank you! We have those, it seems they are all good! My issue now is testing the mats, workbenches, and floors. I am going to try using a multimeter today before but the previous times I have tried it did not seem to work correctly. I will get the 5lb probes and surface tester if needed. \$\endgroup\$
    – MDD
    Commented Mar 6 at 13:03

Not the answer you're looking for? Browse other questions tagged or ask your own question.