Paper and cardboard on the production area

We are a contract manufacturer of printed board assemblies. We have ESD controls in place, but still will find the use of paper on the production area, either lying on top of boards, or taped to the tray. Is this OK?

ESDCOMP,

There is a similar discussion about this topic in the forum and the response (Jeremys in April 2022) was “The problem with paper is it’s a very variable material. Different types of paper vary by orders of magnitude in their basic resistance charcteristics if you were to compare them at a set humidity level. Then, they vary by orders of magnitude in resistance with changes in humidty. Coatings and treatments add another layer of variation. I once measured a range of papers (from my office bin) resistance between 20 %rh and 70 %rh. At 20 %rh they were all >100 GΩ (insulative). at 70 % rh some were in the tens of MΩ range, but a few were still > 100 GΩ. So, if you want to be sure what the characteristics of your paper was, you would need to do a similar experiment with it to find out. Once you have selected a suitable paper, you would need to stick with that make/type and even then occasionally check to make sure no changes have been made that affect its characteristics.”

I agree with this comment. If you determine that the paper in your process is insulative (>10^11 ohms) then you should refer to the ANSI/ESD S20.20 requirements. The first is that you move all non-essential insulators more than 300mm (12 in) away from any ESDS items. If the insulative paper is considered essential to the process then the requirement is that one of the following criteria shall be met:
• Measure the field at the location where the ESDS item is handled. The electrostatic field shall be less than 5000 volts/meter (125 volts/inch).
or
• For any process essential insulators located less than or equal to 25 mm from an unprotected ESDS item, the voltage on the surface of the insulator shall be less than 125 volts when measured with a non-contact electrostatic voltmeter. When using an electrostatic field meter, the reading shall be less than 125 volts when measured at the meter’s stipulated measuring distance.
• For any process essential insulators located more than 25 mm, but less than 300 mm from an unprotected ESDS item, the voltage on the surface of the insulator shall be less than 2000 volts when measured with a non-contact electrostatic voltmeter. When using an electrostatic field meter, the reading shall be less than 2000 volts when measured at the meter’s stipulated measuring distance.

If these requirements are met, you can be more confident that the process can handle the paper with relatively low risk to ESD.

Andy’s response is a thorough summary from the ESD standpoint. The other consideration depending on your customer base is the potential for FoD.