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'[EE] DIY Anti-Static Storage Boxes'
2008\05\05@131847 by piclist

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So I read up on ESD and a few people stress that you do not actually want
conductive storage like those foil bags or black plastic boxes.

It makes sense.  If I have an open box with a part inside, and I reach in
and touch a lead, any static charge on me can go through the chip, into
the box and ground out.  A non-conductive box would not do that.  Of
course grounding yourself before touching anything is better, but mistakes
happen.

One solution I found and wanted an opinion on was from this page:

 http://wiki.xtronics.com/index.php/ESD

 (Hot tip: use an anti-static floor-wax on your plastics and you
 shouldn't have to ever treat them again! Just dip your plastic bins and
 trays in. Then let them drip drain and dry. Think of the antistatic
 floor wax as an almost permanent spray.
 see http://www.rdmoney.com/floor_finish.htm).

Anyone tried this?  I have a lot of storage boxes I use for resistors,
caps and other non transistor based parts, but chips and various bits
find their way into them.  The storage containers rub against each other
and can form a nice static charge by themselves and reaching in for a part
can zap it.  But ESD containers are hard to find and expensive.

If nobody has tried it, I might just grab some of the stuff mentioned in
that link and try it out on a box or two.

--
Ian Smith

2008\05\05@184931 by Brendan Gillatt

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spam_OUTpiclistTakeThisOuTspamian.org wrote:
> So I read up on ESD and a few people stress that you do not actually want
> conductive storage like those foil bags or black plastic boxes.
>
> It makes sense.  If I have an open box with a part inside, and I reach in
> and touch a lead, any static charge on me can go through the chip, into
> the box and ground out.  A non-conductive box would not do that.  Of
> course grounding yourself before touching anything is better, but mistakes
> happen.

There are two reasons for the conductive boxes: firstly so that charge
does not accumulate inside capacitors, and also so that when you reach
inside the box the potential between the fingers is shorted as they touch
the sides.

An insulating box would leave the charge on the fingers and let the
chip's FET's 'absorb' the shock.

'Designers have figured out that it takes a spark to have ESD, so modern
electronic products now have their conductive shielding layers buried in
insulating plastic.' The last chip I topped certainly did not have a
'conductive shielding layer'.'

'The volume conductive plastic, instead of protecting, can actually
produce ESD. The black volume conductive acts as one of the conductors
from our list of requirements to produce ESD!'

So what's the difference between touching the component with a
(conductive) finger or (electrically) touching it with a finger via a a
bit of conductive plastic?

'The parts leads can act as the other conductor.'

Exactly as it would if you were to touch the part with a finger.

I could go on...

I would be wary of that article - it is full of speculation and fairly
confused logic.

- --
Brendan Gillatt | GPG Key: 0xBF6A0D94
brendan {a} brendangillatt (dot) co (dot) uk
http://www.brendangillatt.co.uk
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2008\05\05@190806 by Sean Breheny

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Hi Ian,

I've seen four categories for static characteristics:

1) Insulating - able to generate charge
2) Insulating - unable to generate charge
3) Dissipative
4) Conductive

An example of #1 would be a plastic shopping bag. #2 would be the pink
ESD bubblewrap
#3 would be ESD foam or carbon-filled plastic. #4 would be metal or
high-carbon content plastic.

Generally, #1 should be kept away from ESD sensitive components at all
times. #2 is acceptable when necessary. #3 is the generally preferred
environment for handling. #4 is necessary in some conditions for
storage and transport.

The distinction between #1 and #2 is that #1 is likely to generate a
charge difference when rubbed against either itself or other common
materials. #2 must not do so. #3 must have a resistance of something
like between 10^9 and 10^6 ohms per unit (ohms per square for a
surface coating, straight ohms for a single wire connection). #4 is
anything more conductive than this.

#3 (dissipative) allows charge to bleed off slowly so that it cannot
accumulate or be deposited AND so that it will not suddenly discharge
(like you said). This is why it is best for handling.

#4 can act as shielding. Generally, it is necessary to protect against
not only an actual discharge but also a high E field. Keeping
components inside a shielded container while in storage and transport
allows them to survive being brought near very strong E fields (like
you might find around plastic bags or dry cardboard)

Most of the conductive ESD bags I've seen are actually THREE layers.
The inside and outside are coated in a dissipative material.
in-between is a layer of metal (so thin that you can still see through
it). The dissipative material prevents the bag from making things
worse (by a sudden discharge) and the inner metal forms a pseudo
Faraday cage.

I was under the impression that the black-coated cardboard (like
corstat) is dissipative, not conductive. It is easy to check with an
ohmmeter. Dissipative should show basically no conductivity on most
meters (do not touch the metal probes with your skin - that is
conductive).

So, my understanding of general ESD precautions is this: Components
should be directly packaged in dissipative materials (like ESD plastic
or foam). This, along with an ESD workstation, is best for at-bench
handling. However, whenever components or boards need to leave the
bench (for storage or transport), they should be put in a three-layer
bag (dissipative-conductive-dissipative), and may also still be in
their dissipative plastic or foam. Finally, any packing material used
along with the devices should be either dissipative or non charge
generating (category #2).

Sean


On Mon, May 5, 2008 at 1:18 PM,  <.....piclistKILLspamspam@spam@ian.org> wrote:
{Quote hidden}

>  --

2008\05\05@203344 by Apptech

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> So I read up on ESD and a few people stress that you do
> not actually want
> conductive storage like those foil bags or black plastic
> boxes.


I do the following in some instances.
YMMV.

- Whiff plastic boxes with Zinc electrostatic screening
spray - intended to provide capacitive shielding for plastic
enclosures. A very light layer will provide an ugly speckled
incomplete paint finish that will allow charge to equalise
over container. Available in spray cans. Degree of
conductivity will be controlled within reason by coating
thickness. A little goes a long way.

- Place a sheet of butyl rubber (as used for eg waterproof
roofing and similar) under plastic trays. This is variably
conductive due (I think) to the carbon black loading used in
its manufacture. Two meter probes stuck into surface produce
readings of low k-ohms to megohms, variable by product
source. (This resistance is (ABOUT) the same regardless of
probe separation due to "resistance per square"
effect).Probes laid lightly on surface tend to show high
resistance.  Either end of the above resistance range should
be OK. At the low end you don't want to be placing live
circuitry on the Butyl rubber :-). You COULD provide
earthing straps to the rubber sheets but in most
applications bulk resistance to ground effects will allow
this arrangement to be OK.

As above, YMMV.

I haven't tried but "cold galvanising" paint should provide
a similar effect. I have a 4l tin of this (very old) and it
weighs about a zillion kg so I think the Zinc content in it
is very high. It would ideally want to be thinned down and
then applied in some suitable manner.

My main storage drawers that  use the above arrangement are
wooden - a set of large shallow plan drawers, so the bulk
resistance to ground will be lower than with some synthetic
materials.



       Russell








{Original Message removed}

2008\05\06@022542 by Clint Sharp

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In message <Pine.LNX.4.64.0805051308510.2116@http://www.sportsmogul.com>,
piclistspamKILLspamian.org writes
>So I read up on ESD and a few people stress that you do not actually want
>conductive storage like those foil bags or black plastic boxes.
I'd rather have them than not thanks. I like to be as certain as I can
that the components work when I put them into a circuit.
>
>It makes sense.
No it doesn't. There's a reason why there are only a *few* people who
stress that whilst the majority say you should have dissipative or
conductive storage.
> If I have an open box with a part inside, and I reach in
>and touch a lead, any static charge on me can go through the chip, into
>the box and ground out.
The whole point  of ESD protection is that you have no static charge
when you touch a component and neither does the component. Remember,
static will damage components if it discharges from you or to you though
the component.
>  Of
>course grounding yourself before touching anything is better, but mistakes
>happen.
Of course you are correct that mistakes happen but the chances of
killing things with static is much higher if you don't store them
correctly.
>
>  (Hot tip: use an anti-static floor-wax on your plastics and you
>  shouldn't have to ever treat them again! Just dip your plastic bins and
>  trays in. Then let them drip drain and dry. Think of the antistatic
>  floor wax as an almost permanent spray.
>  see http://www.rdmoney.com/floor_finish.htm).
How are you going to prove it works though? More to the point, how are
you going to prove it's still working if it ever did? Will you be
keeping a tally of dead devices and waiting for the number to rise?
If it's business use then just buy the correct stuff providing you have
the cash flow, if not, get creative until you do.

If it's home use, any decent component supplier should use proper ESD
packaging so leave the stuff in that until you use it and re-use the
better quality packaging to build yourself a storage system.
>
>--
>Ian Smith

--
Clint Sharp

2008\05\06@073158 by Apptech

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>>  (Hot tip: use an anti-static floor-wax on your plastics
>> and you
>>  shouldn't have to ever treat them again! Just dip your
>> plastic bins and
>>  trays in. Then let them drip drain and dry. Think of the
>> antistatic
>>  floor wax as an almost permanent spray.

I maent to add - antistatic sprays that are meant to make
conditoons acceptable for people may well not reduce ESD to
the level that works OK for all components. The general
consensus in years gone by [tm] was that they were not good
enough.

> How are you going to prove it works though? More to the
> point, how are
> you going to prove it's still working if it ever did?

A foil electrometer / electroscope is cheap and easy to make
(and maybe even to buy) and will give a good idea if ESD
protection is working.

OR here's a FET electroscope that can be adapted. Cheap and
easy

       http://www.eskimo.com/~billb/emotor/chargdet.html

   http://www.nfinity.com/~exile/electro.htm

   http://www.mos.org/sln/toe/simpleelectroscope.html

$17 - out of stock

   http://www.physlink.com/estore/cart/GoldFoilElectroscope.cfm

$32

  http://wardsci.com/product.asp?pn=IG0008328&bhcd2=1210072291




       Russell


2008\05\06@185617 by Nate Duehr

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piclist@ian.org wrote:
> So I read up on ESD and a few people stress that you do not actually want
> conductive storage like those foil bags or black plastic boxes.
>
> It makes sense.  If I have an open box with a part inside, and I reach in
> and touch a lead, any static charge on me can go through the chip, into
> the box and ground out.  A non-conductive box would not do that.  Of
> course grounding yourself before touching anything is better, but mistakes
> happen.

You shouldn't be "reaching in and touching a lead" before you're
adequately connected to the ESD workstation ground.

Nate

2008\05\07@105051 by piclist

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On Tue, 6 May 2008, Nate Duehr wrote:
> You shouldn't be "reaching in and touching a lead" before you're
> adequately connected to the ESD workstation ground.

If I had a workstation for my projects that would be great. :-)

But you are right.  I do have a ground strap running along the side of my
desk for both working with computer parts as well as electronics.  

Most of my parts are in EDS bags or black conductive boxes.. chips stuck
in conductive foam.  I just wish I had ESD versions of the containers I
use for non-sensitive parts.  I like having things sorted so I know what
I have and also can find it.  A big bag of parts while safe in the
sheilding, is not very safe once I dump it onto my desk to find the
part I need. :-)

I don't think they even make EDS storage boxes with clear lids, which is
what I would really like to have a dozen or more of.  I guess the only way
to make plastic safe is to fill it with carbon or coat it in something.

--
Ian Smith
http://www.ian.org


2008\05\07@110955 by Sean Breheny

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Hi Ian,

I am pretty sure they DO have ESD boxes with clear lids:

http://www.all-spec.com/1/viewitem/SM0882/ALLSPEC/prodinfo/w3path=cat

This particular one is conductive (I think you would want dissipative,
but I suspect that is available too).

Sean


On Wed, May 7, 2008 at 10:50 AM,  <.....piclistKILLspamspam.....ian.org> wrote:
{Quote hidden}

>  --

2008\05\07@112143 by Apptech

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> Most of my parts are in EDS bags or black conductive
> boxes.. chips stuck
> in conductive foam.  I just wish I had ESD versions of the
> containers I
> use for non-sensitive parts.  I like having things sorted
> so I know what
> I have and also can find it.

> A big bag of parts while safe in the
> sheilding, is not very safe once I dump it onto my desk to
> find the
> part I need. :-)

Get a sheet of Butyl rubber, such as I suggested before.
Take meter to place of sale. Stick meter probes into sheet
on megohms range. ANY ohms reading is OK. Some few types
I've met had no reading but almost all have some. Some are
very low R and are a hazard to PCB operation if an operating
cct is placed on the sheet.

Here local suppliers get material wrapped in Butyl rubber
outers and they sell them for staff Christmas party funds.
Much cheaper than buying new BUT even at new prices Butyl
rubber costs <<$ than "proper" electrostatic mats.

You can also line draws with BR sheet.

> I guess the only way
> to make plastic safe is to fill it with carbon or coat it
> in something.

OR read my prior post.
Zinc electrostatic shielding spray whiffed on lightly. Or,
perhaps, "cold galvanising" paint.



       Russell


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