A lot of the stuff we help to create is used in industrial manufacturing. Now it happened,
that we were contacted by two seperate customers in one week, who asked about
the ESD capabilities of the product they use. (Totally different products for unrelated processes.)
Question 1: What is going on? Has a new standard been set for production equipment to be “ESD resistant”?
Question 2: Currently whe use mostly ABS plastics. Is anyone of you aware of an alternative, that retains the
mechanical strenght of the ABS but helps against the electrostatic charging of said components?
In former times graphite powder has been used as an additive, but that didn’t create usable results.
Thank you in advance for any hints to materials or even possible suppliers.
ESD for consumer electronics is generally taken into effect whether it is specified or not. You don’t want your product to not function correctly, or have a component failure after zapping it. Case in point - some of our old scanner products would be effected by ESD, which you can imagine is a problem if the scanner resets in the middle of a transaction - something that could happen, especially in the winter months when a retail cashier might be folding up a bunch of sweaters that then zap the product.
Generally we don’t consider material for ESD purposes - we consider the mechanical design and ESD path. IE when the product gets zapped, where is the discharge going to go. Usually for certain specifications you need a longer distance from air gaps in the product to the PCB, which can also be achieved by adding ribs or other internal features to increase the distance the discharge has to travel.
Or is there a concern that the product you are designing may be able to transfer it’s own discharge to some other piece of equipment? (IE a pair of tweezers carrying a charge to a chip during assembly?)
Thanks for your reply Mike. Unfortunately it is the latter scenario. So we really have to
think about the material, as we can’t influence the path of interaction with other items.
But would love to get some hints before I have our sourcing contact the plastics suppliers
about this next week. They’ll give me results, but I need somebackground to gauge these
results against.
Yeah, I’m no expert on what materials are/aren’t the most conductive (there is an “electrical” spec in some resin data sheets I’ve seen from Sabic, but no idea what they mean in relation to ESD).
No new standards I’m aware of regarding static dissipative levels of production equipment. It becomes an issue in environments with explosion risk: volatiles, dusts. Or where the process itself is susceptible to static buildup such as paper handling and some dry foods processing.
Just about all plastics are susceptible to static surface charge buildup, just the action of airflow over the plastic surface, over time, is enough to build up a charge, so is the mundane action of removing a plastic housing device from a foam cushioning travel case enough to actually cause a static discharge spark.
Plastics material conductive fillers do not work well, regardless of specification or whatever people tell you. Sure, there’s conductive plastics and carbon and metal fillers, but they don’t work well and they don’t work for long. Bulk fillers are processed to not migrate to the surface of plastic parts during molding as most bulk fillers are ugly and quite noticeable on the surface. As static electricity is a surface charge, intentionally processing conductive fill away from the surface inherently makes so called conductive plastics not good at ESD. Frustratingly, a conductive fill actually can work but it’s very inconsistent as the fill dispersion is not homogenous and different part to part: stab electrical test leads into a conductive filled plastic part at different points and you’ll get dramatically different resistivity readings.
So, I designed several lines of portable gas detectors, all requiring electrical safety certification for explosive environments. For the highest safety rating, the only solution for surface ESD was a conductive carbon spray. It turned the nice surface texture molded plastic housings into what looked like a too heavy paint job. To be clear, the devices, with carbon spray coatings, were tested at safety certification laboratories both in US and EU, so there are standards, but they’re a bit usage location specific.
However, Xerox and competitors face this issue in photocopiers, as described to me by one of their engineers. I don’t know exact details of how they do it, but it appears they use lots of ground return cables and small brushes to constantly drain charge?
