"esd safe" insulating material?

[jeremy]

Hi,

I often have this problem, but don't know the proper answer to it, so I was hoping that someone could point me in the right direction.

I have a bare PCB which is being tested on an ESD mat. However, it seems that due to the conductivity of the ESD mat, there is some slight leakage which is affecting the measurements (I think...). What is a good material to put between the ESD mat and the PCB to insulate the two from eachother? Ideally, I'd like to put something like a 2mm thick piece of acrylic, but I know that acrylic is very good at holding static charge, so that's probably not a good idea 

[Siwastaja]

I would consider the pink "static dissipative" ESD bags for this purpose.

These bags are used to package ESD sensitive components inside their ESD shielding packs - the idea is, while they won't protect the components from ESD shocks (hence, external ESD control, like the ESD pack, or in your use case, your ESD mat, is needed), they won't generate charge themselves too easily.

[Gyro]

It's pretty hard to build up a significant charge on cardboard. 

[LukeW]

I think what you're asking for is intrinsically impossible.

Any good insulator will allow charge accumulation, and any ESD-dissipative material must be at least slightly conductive.

You have to find the right balance, the right tradeoff in the resistivity of the material, for your application.

[helius]

Does your board have any mounting holes? Try elevating it above the mat using metal standoffs. That will provide a path for static charges to pass to ground (via the mat) but not load any sensitive nodes on the board.

[jeremy]

Thanks for the replies.

helius: In this case, no, but I am looking for a general solution

LukeW, anti-static materials do exist that are not conductive, they just resist charge buildup using via the triboelectric effect. This is the main difference between "anti-static" and "static dissipative" materials.

Gyro: thanks, I will have to look into this. I was thinking paper or something similar might work

Siwastaja: Actually, I'm using those blue digikey bags right now. Also that pink foam that stuff sometimes gets shipped in. I just don't know where I can get large pieces of it (say, A3 or A4) without just trying to buy the largest item I can find at digikey...

PS fun fact: I ordered a TI book from digikey once (as in made of paper), and it came double bagged in static dissipative and anti static bags