ESD exposure to components installed in open metal enclosures

I’m a supervisor of an engineering development lab and have an issue regarding an audit finding. What if any is the ESD exposure risk to ESDM installed in/on metal enclosures/ card cages (unpowered), that have exposure on one side (open access).

Hello, that is somewhat of a difficult question to answer. One answer would be that if any of the exposed connections on the back could lead directly to an ESDS item, it can be considered an ESDS item. Therefore you need to take measures to ensure there is no exposure.
However, if you can make the point that the exposed back presents no risk to an ESD event, then you could classify the part as not sensitive and no further action would need to be taken.
Last point, if this is truly an engineering part and will not be shipped to a customer (and you can prove it) you could take the risk internally and tailor your program to exclude the lab. A good assessor will ask to prove that the item cannot be shipped to a customer. In this case the part needs to be traced.

Hope this helps.

Thank you for your quick reply. My understanding was that the metal mass of the enclosure around the ESDSM would absorb and dissipate a static charge (depending on its size) before it was introduced onto the ESDSM or is that incorrect? I also had a question on ESD bags within a EPA, My understanding was that they don’t have to be sealed until they leave the EPA?

Hello, again this is a bit difficult to answer without seeing the card layout. If the card were totally enclosed in a metal housing, it would most likely be protected from an ESD event. As stated before, if only the device was enclosed or only one side was enclosed and there were traces on the backside exposed, it still could be considered an ESDS device.

Within an EPA, typically ESD Shielding bags do not have to be sealed. I would review the procedures to ensure that when the cards are being removed, all ESD control precautions are in place.

When leaving the EPA, a bag should be sealed by some method. Simply folding over the edge and securing with a label or tape would be enough.