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Thanks, I cant find it now, but I had a discussion on edabord some months back where we considered the acceptable resistance of ESD mats etc. The conclusion from some edaboarders was that if the resistance of ESD mat/flooring etc is too low, then it can actually exacerbate ESD damage, because the low resistance means a high surge current spike from an ESD discharge. I’m not sure if this is true? The concensus seemed to be that the resistance to earth of an ESD mat or floor should be around 1 to 2 Megohms…….if any more or less than this then ESD protection is not optimised?I do know of one building where military aerospace parts are made that has a solid copper floor
Thanks, i wonder if we can just do a cheap esd tile resistance measurement method by putting loads of copper tape over the esd floor tiles, and then connecting to these two separate patches of copper tape with the normal , pointed DMM probes?Yes, you can make your own contact probes. They wouldn't be certified to meet standards unless you submitted them to a test lab but they should work perfectly well.
Thanks, though say a PCB worker goes to the toilet, and then comes back into the ESD sensitive area, then on their way back from the toilet they may have picked up a charge and so it would be best if they could discharge this when coming back into the ESD sensitive area?the idea of these devices isn't to be able to discharge an existing voltage, they are to prevent it building up in the first place so a slow drain through high resistance is quite in order.
Thanks, though i am surprised they are not zero ohms, since the 1 Meg would be provided by the resistance from the floor tiles to the earthing point?ESD shoe straps are typically equivalent to wristband resistors at about 1M.
The amount of charge they accumulate should be fairly small, it is mostly capacitance to ground which will only be a few hundred pF at most and assuming they don't remove their shoe strap it will disappear within a few seconds.they may have picked up a charge and so it would be best if they could discharge this when coming back into the ESD sensitive area?
Thankyou, sorry to keep asking, please dont answer if youd rather not. At what point do you believe they will dischareg the charge they have built up after coming back to the esd area from say the toilet etc?......when they put on the wriststrap which is attached to earth on their bench?....for us, that is too late, we want people to be discharged as they come into the esd room.... either via the flooring or something else.The amount of charge they accumulate should be fairly small, it is mostly capacitance to ground which will only be a few hundred pF at most and assuming they don't remove their shoe strap it will disappear within a few seconds.
Use an earthed (with series resistor) metal door or at least a metal door handle....for us, that is too late, we want people to be discharged as they come into the esd room.... either via the flooring or something else.
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