Project Box Material: ESD concerns

FlyingFishFinger

Hi friends-
We are building a custom box to house logic circuitry. I was told at JPL by my supervisors that plexiglass is a terrible material to use because it accumulates static charge like no other. Is this true, and if so, what would be a good clear material to use for a box?
Thanks

Rafael

Franklin

Transparent Aluminum

(Captain, thar be whales.)

Phil Pilgrim (PhiPi)

You can always spray the inside of a plastic box with anti-static paint. It may not be as clear as you want it, though.

-Phil

Peter KG6LSE

I have seen ESD safe Polycarb .is easy to work with just like normal polycarb.


http://www.esdproducts.biz/CleanroomProducts/ESDSafePlastic/PC350Polycarbonate/pc350polycarbonate.html

Unknown

What size ESD could penetrate it? What would be the rule of thumb?

They say lead or dirt is the only thing that can stop radiation.

Peter KG6LSE

ESD isnt a penetration function in the same sense as Alpha particles .its a build up of charge on a serfice Like a capacitor .. In theory One could dump a Boat load of amps at a obscene voltage and vaporize the ESD coating . My 10 KW Tesla coil / Lightning may do it , but I doubt doing a jig on the carpet in summer will obliterate the ESD coating .


What do you need ESD protection from ?
Casual normal human use?

Little side note : I read a few years back that some lab-wear that is made from acrylic is ∂ radiation resistant . ( the diagger scientific catalog has them ).

LoopyByteloose

This all seems to be a case of 'technical paranoia' which usually occurs from reading too many disclaimers from manufacturers. Experience is the cure. As you use the box, I suspect you will see that you don't have any problems unless your environment is hostle in the extreme.

FlyingFishFinger

You may be right. We don't actually have any experience with things blowing up from ESD, but so far the only thing we have in an acrylic / plexiglass box (not sure which) is non-logic stuff. We can't really afford to "build it and see if it fries" for the new one though. The environment is going to be the middle of Australia in the middle of summer, but I'm not too sure what that says about ESD buildup. Hot & dry = bad, so I've heard.
Hence the question, do we need to design with this in mind?

LoopyByteloose

My reply was intended for the 'average hobbyist use'. Now I see JPL and assume that means Jet Propulsion Lab, a government agency.

So I am not at all clear on the level of expectation about reliability or the need for such.

There also seems to the the assumption that the box has to be clear plastic as well as ESD. From what little I know of clear plastic is that it is far more unstable in direct sunlight than black plastic.

All this seems to point toward an aluminum box with a glass window and having the box grounded. After all, why does everything have to be plastic these days? Don't dust and sandstorms creat substantial static?

FlyingFishFinger

Oh, this isn't actually meant for JPL.
I interned there over the summer and sought advice about this box, and that is what they told me. It is a circuit board box for the solar car.

So far, we've decided to go with some sort of esd-treated polycarb for ease of assembly because Vector retracted their sponsorship offer because of a disagreement with our contact (they were going to make us a custom aluminum box with racks).

LoopyByteloose

Here in Taiwan we have tons of plastic bodied motor scooters on the road in tropical sunlight. The amusing thing is that plastics of all sort begin to rot from solar exposure after about five years and the much older scooters are interesting in how they crumble.

But, when compared to a Vespa (a steel bodied scooter), the lighter weight is a huge advantage in terms of fuel consumption and safety (due to reduced collision impact).

Steel is obviously heavy, aluminum is half the molecular weight of steel, but plastic will always come in lighter than either of them. Amusingly, the weight of a cubic foot of aluminum is about 5 pounds heavier than a cubic foot of concrete. So it looks like 'go ahead with plastic of some sort.'

I still don't quite know how to resolve potential static problems as they evolve. And it certainly is a bit difficult to duplicate in a controlled environment, but a Van de Graaph generator might be helpful to do some testing. Parallax's microcontrollers seem rugged and have diode clamps on all I/O. Much depends on your generation of MOS logic that you choose for support. And I suspect at the end of the day, you will find yourself wondering until you transit Australia and discover what the real performance issues are.

What you really need is someone who has been there and tried things. Try some Aussie web sites.