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Question Dear sir. We are contract manufacturer. In our manufacturing floor, paper are used as a reject tag, travelers which in contact with the pcba. Our manufacturing floor is control at 40-60 % RH. Question: Can papers at this environment be a threat to ESD event?

This should be a simple question, and I probably will provide you with too much information.

I think the answer is no. Paper is hygroscopic (readily absorbs moisture) so your paper likely measures <10E11 ohms and would be low charging. Charges would be removed to ground when the board and paper were placed on a properly grounded ESD worksurface or handled by a properly grounded operator. To support using your paper as is, one could measure static charges using a Static Field Meter, and/or measure the paper’s resistance using a Surface Resistance Test Kit.

However, best practice would be to use dissipative tags and paper or place insulative paper in Dissipative Document Holders.

This citation was in the ESD Association’s ANSI/ESD S20.20-1999, however it has been removed from the 2007 revision (This text might be put in the upcoming revision of ESD Handbook ESD TR20.20):

“All nonessential insulators, such as those made of plastics and paper (e.g. coffee cups, food wrappers and personal items) must be removed from the workstation. Ionization or other charge mitigating techniques shall be used at the workstation to neutralize electrostatic fields on all process essential insulators if the electrostatic field is considered a threat.” [ANSI/ESD S20.20-1999 section]

The European standard is even stronger requiring “Paperwork inside the EPA [ESD Protected Area] shall either be kept in containers conforming to the requirements of table 2 or shall not generate a field in excess of that specified in paragraph 5.3.5 [ESDS should not be exposed to electrostatic fields in excess of 10 kV/m].” [EN 61340-5-1 clause 5.5 EPA working practices]

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