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Posted by jc-Atl on September 29, 2005, 8:26 pm
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Hi guys - I figured this group is as good as any other for this question:
At a new contract I am on, we have an embedded Linux card --- a Cogent
CSB626 , etc.
A coworker told me today that the card must remain on the static protective
bag it came in (while powered up). It has metal standoffs. I said it was
better off not staying on that in case someone moved it and the bag came
into contact with the solder points on the card and shorted it out. I have
been placing it back in the bag (powered off) at the end of each day before
I leave.
The static bad is the kind with the thin metalized coating that you can
partially see through.
What do you guys think ?
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Posted by howy on September 30, 2005, 11:54 am
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take an ohm meter to the bag and you may find that the bag is barely
conductive, The biggest problem you should have with static is when
the device is hooked up to a power supply and is grounded thru a number
of different instruments. In the winter you will be zapping the board
on a daily basis.
I have never dammaged a device by zapping it in the last 5 years. The
parts you have to watch out for are devices that are designed to run at
very low power levels like real time clock chips, battery-backed RAM
and maybe MCUs that draw a few micro amps. These parts can be dammaged
easily.
-howy
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Posted by Ben Bradley on September 30, 2005, 10:13 pm
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>Hi guys - I figured this group is as good as any other for this question:
>
>At a new contract I am on, we have an embedded Linux card --- a Cogent
>CSB626 , etc.
>
>A coworker told me today that the card must remain on the static protective
>bag it came in (while powered up). It has metal standoffs. I said it was
>better off not staying on that in case someone moved it and the bag came
>into contact with the solder points on the card and shorted it out. I have
>been placing it back in the bag (powered off) at the end of each day before
>I leave.
>
>The static bad is the kind with the thin metalized coating that you can
>partially see through.
>
>What do you guys think ?
I think:
It should come out of the bag and stay out when you're ready to use
it.
It should stay in the bag until you're ready to plug it up and
power it up (I think you're past this point).
It won't much matter electrically if it's in the bag, because the
bag's resistance is rather high (in the high megohms, but this is
still plenty low enough to discharge any static charges) and won't
conduct electricity enough to affect most circuitry. Try measuring the
resistance of the bag. It's a lot higher than your the resistance of
your skin.
It should stay out of the bag when powered up because it will hold
heat in and if the board dissipates significant amounts of heat, it
could overheat in the bag.
I think that's everything I think on the matter.
Well, no. The main problem with static discharge is when you walk
across the room and touch something such a gate input. The first thing
you should touch when you arrive at a workstation is a "ground"
connection TO THE DEVICE YOU'RE GOING TO WORK ON. This would be the V-
connection of a bench power supply you're running it on, or the metal
shell of a DB-9 that gives a serial or programming connection between
the board and a desktop computer. Perhaps the next thing you should
touch is a wrist grounding strap as you put it on (these things have
about a 1 meg resistance to actual ground, so if you end up touching
220V with your other hand you may feel a slight shock instead of a
deadly one).
If you disconnect the board it and move it to another lab, or ship
it across the world, it would be a Good Thing to put it in the bag as
soon as you disconnect it, but not when it sits connected (powered pr
not) on the bench overnight. Static problems come up in handling the
thing, not when it sits still.
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>
>At a new contract I am on, we have an embedded Linux card --- a Cogent
>CSB626 , etc.
>
>A coworker told me today that the card must remain on the static protective
>bag it came in (while powered up). It has metal standoffs. I said it was
>better off not staying on that in case someone moved it and the bag came
>into contact with the solder points on the card and shorted it out. I have
>been placing it back in the bag (powered off) at the end of each day before
>I leave.
>
>The static bad is the kind with the thin metalized coating that you can
>partially see through.
>
>What do you guys think ?