After a recent audit, it was noted that our practice of placing PCBA magazines on plastic pallets does not meet ESD compliance standards. The PCBA magazines we use are not completely enclosed Faraday cages, which means they do not provide full protection against electrostatic discharge (ESD) when placed on plastic pallets.
i attach the picture of pcba magazine
According to my limited knowledge ,
Basically for any ESD control facility fundamental requirement is availability of an effective common ground for the entire facility . Including the Personnel and anything and everything that is used in an EPA should either be properly grounded to a common ground or should have a provision for static neutralization by ionizers where practical conventional grounding is not possible.
The frame and the sliding arrangement in a PCBA magazine racks are normally of SS or Aluminum and the slotted racks shall be of conductive plastic and there by the total system can be grounded if kept on a grounded surface but not on an insulator ( surface of plastic pallet ). This is the common mistake in most of the facilities . Since the PCBA magazine racks are open but not enclosed fully like static shielding bags or conductive boxes it cannot provide the Faraday cage protection but however if the rack is grounded or kept on a grounded surface it does provide some protection against the possible ESD damage.
I hope ESDA the experts would share more explanation .
The PCBA magazine may be adequate, but you would need to measure it to see the effect of any electric field produced by the plastic pallet. This would be best accomplished by using a high impedance contact voltmeter to measure the voltage of the PCBAs in the PCBA magazine while in normal use and then compare it to your limits.
If you were interested in a worst-case analysis, you could artificially charge the plastic pallet as much as could be expected in the process and then measure the voltage and compare to the limit.
If you don’t have a high impedance contact voltmeter you could also use a non-contact voltmeter or possible a field meter but there are draw backs in getting an accurate reading for voltages close to the limit.
If your measurements are outside the limits, you could consider trying metal plates underneath, above or on the sides of the PCBA magazine as this will improve the amount of voltage suppression but, again, you would need to measure to verify.
Another potential solution rather than metal plates is simply an ESD mat like used on workstations. i dealt with a similar issue recently where a couple of magazine “lift” carts were acquired that could lift the magazines to a more manageable height for placing in a loader/unloader. The deck of the lift was painted and found to be highly insulative. the voltage levels were considered minor risk after measuring during normal use. We placed 2 layer ESD mats on the lifts to provide a “safer” environment and found the voltage measurements were greatly reduced.
