Suppose you have a static/ESD shielding grey bag housing electronics sensitive to ESD. I believe that this type of bag has a static dissipative surface and a conductor on the inside serving as a Faraday cage. While these bags offer a high level of protection, they don't shield the contents 100% from static electricity.
Now suppose you have a setup where you have a static dissipative mat, you are connected by a static dissipative wrist strap to the mat, and the bag is placed by you onto the mat while wearing the wrist-strap. However, the mat is not grounded externally to a true ground, but connected to a metal object, e.g. a metal computer case. As I understand it, after being placed on the mat, you, the metal object, and the bag are at the same voltage/potential (not zero, and so different from the question in How should I use a static-shielding bag prior to opening, and why?)
My question is: is it safe from an ESD standpoint to then remove the ESD sensitive electronics from the bag (possibly handling them via a grounding plane on the electronics)? In other words, are the contents of the bag at the same potential as your hands or the mat? If it's not safe, is there a safe way to do this without potentially causing damage, or does the mat necessarily have to drain charge to a true ground?
The reason I ask is that I see this ESA setup recommended here and there in this and other stack exchanges (https://superuser.com/questions/975427/how-to-properly-use-an-antistatic-wrist-strap-when-working-on-a-desktop-pc), and the ANSI standard S20.20 talks about equipotential bonding.
I am wondering if someone would be able to answer with the appropriate theory, whether or not charges between one's hands and the contents of the bag will equilibrate/equipotential bond when handling a static shielding bag or when it is placed on a static dissipating surface.
Best Answer
I've successfully used this mindset --- get the person, the bag, and the sensitive circuit to be at the same potential --- with NO ESD damage, on numerous sensitive projects.
I guide people with ---- find the GROUND pin on the PCB, and first touch that.
Now you can remove or insert whatever you want from or into the PCB, safely.