Limit for Discharge Shielding < 20 nJ

Dear all ESD expert,

Could you please explain the limit for discharge shielding come from?
How it related with ESD sensitive level in term of CDM?

The short answer is, the energy in the Human Body Model at 100 volts is approximately 50nJ. Since packaging is really to protect discharges from people, the original limit was 50nJ. It has been found that shielding bags typically are about 8 to 15 nJ so the limit was lowered.
This limit only applies to the size bag in ANSI/ESD STM 11.31 and other bag sizes will differ. This method is intended to measure the metal around the bag as that cannot be measured directly.

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Hello John

Thank you so much for your answering. It is very helpful for more understanding.