Is it safe to keep the CMOS chips (RAM) in plastic box?
if not, can it be modified to be safe somehow, I just don't have any
alternative..

"orange" wrote in message
...
Is it safe to keep the CMOS chips (RAM) in plastic box?
if not, can it be modified to be safe somehow, I just don't have any
alternative..


Wrap some aluminium foil around a small piece of expanded polystyrene, then
you can just push the chips into the sandwich and keep the lot in a plastic
box. The foil shorts all the pins together so there can be no potential
difference between any.


Gareth.

gareth magennis wrote:

"orange" wrote in message

Is it safe to keep the CMOS chips (RAM) in plastic box?
if not, can it be modified to be safe somehow, I just don't have any
alternative..

Wrap some aluminium foil around a small piece of expanded polystyrene, then
you can just push the chips into the sandwich and keep the lot in a plastic
box. The foil shorts all the pins together so there can be no potential
difference between any.

Aluminium foil is a BAD idea. In the event that there is any appreciable charge
on a given pin, pushing it into aluminium foil will discharge it *quickly* and
the resulting current may kill it.

Always use high resistance material for storing ICs like the anyi-static black
foam material. This allows any charge to 'leak' away slowly and safely.

Graham

In article ,
Eeyore wrote:
Wrap some aluminium foil around a small piece of expanded polystyrene,
then you can just push the chips into the sandwich and keep the lot in
a plastic box. The foil shorts all the pins together so there can be
no potential difference between any.

Aluminium foil is a BAD idea. In the event that there is any appreciable
charge on a given pin, pushing it into aluminium foil will discharge it
*quickly* and the resulting current may kill it.

I've just received some kits from Jaycar where they've used this very
method. I must admit to being surprised - everyone else seems to use the
correct foam.

--
*We are born naked, wet, and hungry. Then things get worse.

Dave Plowman London SW
To e-mail, change noise into sound.

"Dave Plowman (News)" wrote in message
...
In article ,
Eeyore wrote:
Wrap some aluminium foil around a small piece of expanded polystyrene,
then you can just push the chips into the sandwich and keep the lot in
a plastic box. The foil shorts all the pins together so there can be
no potential difference between any.

Aluminium foil is a BAD idea. In the event that there is any appreciable
charge on a given pin, pushing it into aluminium foil will discharge it
*quickly* and the resulting current may kill it.

I've just received some kits from Jaycar where they've used this very
method. I must admit to being surprised - everyone else seems to use the
correct foam.



Are there any Data to show the actual risk involved using this method? I
accept that best practice is always best, but what do we know about the
reality of the situation?
Don't forget we are discussing the storage of small numbers of IC's in
somebodys workshop.



Gareth.

Gareth Magennis wrote:

"Dave Plowman (News)" wrote
Eeyore wrote:

Wrap some aluminium foil around a small piece of expanded polystyrene,
then you can just push the chips into the sandwich and keep the lot in
a plastic box. The foil shorts all the pins together so there can be
no potential difference between any.

Aluminium foil is a BAD idea. In the event that there is any appreciable
charge on a given pin, pushing it into aluminium foil will discharge it
*quickly* and the resulting current may kill it.

I've just received some kits from Jaycar where they've used this very
method. I must admit to being surprised - everyone else seems to use the
correct foam.

Are there any Data to show the actual risk involved using this method?

See manufacturers' advice.


I accept that best practice is always best, but what do we know about the
reality of the situation?
Don't forget we are discussing the storage of small numbers of IC's in
somebodys workshop.

A small sheet of conductive foam isn't expensive and I keep all the small
pieces that ICs come shipped in. These often fit small storage drawers very
nicely.

Graham

Eeyore wrote in
:



gareth magennis wrote:

"orange" wrote in message

Is it safe to keep the CMOS chips (RAM) in plastic box?
if not, can it be modified to be safe somehow, I just don't have any
alternative..

Wrap some aluminium foil around a small piece of expanded polystyrene,
then you can just push the chips into the sandwich and keep the lot in
a plastic box. The foil shorts all the pins together so there can be
no potential difference between any.

Aluminium foil is a BAD idea. In the event that there is any appreciable
charge on a given pin, pushing it into aluminium foil will discharge it
*quickly* and the resulting current may kill it.


It is NOT the current that kills CMOS, it is high VOLTAGE that punches
holes in the insulating layers inside the chip. [I am not aware of ANY chip
families where tiny CURRENTS would be a hazard].

As the conductors are quite small, it only requires a surplus/deficit of a
"few" electrons to build up a high voltage.

When the chip is in a circuit, there will be much higher currents charging
and discharging the

You want to avoid anything that may have accumulated a large surplus or
deficit of electrons.

As long as the aluminum foil is not at a high static voltage, the chances
of damage are quite small.

Hold the chip in one hand, the aluminum foil in the other and run your
finger along the leads before you bring the chip into contact with the
aluminum foil, if you want to 'slowly discharge' any charge that might have
built up.
(this assumes clean hands with normal skin resistance)
If you want to be ULTRA safe, make sure you touch the Vcc and Gnd pins
FIRST.




Always use high resistance material for storing ICs like the anyi-static
black foam material. This allows any charge to 'leak' away slowly and
safely.






--
bz 73 de N5BZ k

please pardon my infinite ignorance, the set-of-things-I-do-not-know is an
infinite set.

remove ch100-5 to avoid spam trap

bz wrote:

Eeyore wrote

Aluminium foil is a BAD idea. In the event that there is any appreciable
charge on a given pin, pushing it into aluminium foil will discharge it
*quickly* and the resulting current may kill it.

It is NOT the current that kills CMOS, it is high VOLTAGE that punches
holes in the insulating layers inside the chip. [I am not aware of ANY chip
families where tiny CURRENTS would be a hazard].

These are two different things. Those 'tiny' currents can be quite large when
discharging a significant charge. Enought to damage the chip's internals
through overcurrent.

Graham

Eeyore wrote in
:



bz wrote:

Eeyore wrote

Aluminium foil is a BAD idea. In the event that there is any
appreciable charge on a given pin, pushing it into aluminium foil
will discharge it *quickly* and the resulting current may kill it.

It is NOT the current that kills CMOS, it is high VOLTAGE that punches
holes in the insulating layers inside the chip. [I am not aware of ANY
chip families where tiny CURRENTS would be a hazard].

These are two different things.

Yes.

Those 'tiny' currents can be quite large
when discharging a significant charge.

Yes, but you can not 'have a significant charge' on a chip without having
a high voltage differential between the chip and the conductor! There are
not enough charge carriers to produce a high current from the small
internal capacitances of the cmos chip itself. If you have enough of a
differential between leads on the chip to cause a high current, then you
have already lost the chip due to the high voltage.

Enought to damage the chip's
internals through overcurrent.

NO! The danger to cmos from static electricity is not due to over-current,
it is due to high voltage differential between high impedance gates and
the base substrate of the cmos chip.

The voltage punches a hole in the insulating oxide layer.

TTL chips and the gated devices in ICs can be damaged by excess current
but that current is from a current source, not the kind of small static
charge that is developed when you carelessly handle a cmos chip.

The use of aluminum foil for storage of static sensitive components is
safe because there can not be an 'appreciable charge' on a given pin
without the device already having been destroyed by the voltage!

Do some calculations and see what kinds of voltage one would need to
produce enough coulombs of charge carriers to produce damage from
excessive current on any IC. Remember, you have only the volume of the
metal conductors involved to hold those charges.

Envision a capacitor, fully charged (the floating gate). Charge it to the
MAXIMUM voltage that it can stand. Now throw a DEAD SHORT across the leads
that feed that capacitor and look at the current flow as the cap
discharges.

Compare that current with the normal charge/discharge currents that flow
as pulses drive the gate when the IC is mounted and being used normally.
Look at the rise and fall times. Look at the conductor materials used on
the chip and connecting the chip to the lead. Find the weakest point along
the current path and compute the maximum peak current that can flow in
that conductor and for how long that current can flow before it causes
damage. [remember, current causes damage by heat.]

Now, check to see if the max permissible voltage could possibly produce
that current.

I think you will find that even chips that have built in weak conductors
['fuses' designed to be burned open by current flow] could not possibly be
damaged by the small charge allowable between any two pins of a CMOS
device.

Now, there MIGHT be some conditions where metal foil would NOT be a good
idea, like those where electrolysis could develop, but we are not
discussing those.

Another condition would be where there are high intensity ELECTRIC fields
nearby, STRONG Pulsed magnetic fields or RF fields nearby. [such as EMP]
But then the chip would be destroyed even if it were soldered into a
circuit.

I have worked with components that are VERY static sensitive (point
contact detector diodes used in radars) that were ALSO easy to damage with
excessive current.

We sometimes had RF fields around that could cause excessive current flow.
We kept the diodes wrapped in foil until we were installing them.

There are times when EM shielded rooms, anti-static mats and wrist straps
are not available. When they are not available, I work on a sheet of
aluminum foil and make sure I touch the foil and the component before the
component touches the foil.

--
bz

please pardon my infinite ignorance, the set-of-things-I-do-not-know is an
infinite set.

remove ch100-5 to avoid spam trap

Eeyore writes:

gareth magennis wrote:

"orange" wrote in message

Is it safe to keep the CMOS chips (RAM) in plastic box?
if not, can it be modified to be safe somehow, I just don't have any
alternative..

Wrap some aluminium foil around a small piece of expanded polystyrene, then
you can just push the chips into the sandwich and keep the lot in a plastic
box. The foil shorts all the pins together so there can be no potential
difference between any.

Aluminium foil is a BAD idea. In the event that there is any appreciable charge
on a given pin, pushing it into aluminium foil will discharge it *quickly* and

And how would this occur?

the resulting current may kill it.

Always use high resistance material for storing ICs like the anyi-static black
foam material. This allows any charge to 'leak' away slowly and safely.

Aluminum foil is fine. The black stuff has a relatively low resistance
anyhow. Check it with an ohmmeter.

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Repair | Main Table of Contents: http://www.repairfaq.org/REPAIR/
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Important: Anything sent to the email address in the message header above is
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subject line. Or, you can contact me via the Feedback Form in the FAQs.

Sam Goldwasser wrote:

Eeyore writes:
gareth magennis wrote:
"orange" wrote in message

Is it safe to keep the CMOS chips (RAM) in plastic box?
if not, can it be modified to be safe somehow, I just don't have any
alternative..

Wrap some aluminium foil around a small piece of expanded polystyrene, then
you can just push the chips into the sandwich and keep the lot in a plastic
box. The foil shorts all the pins together so there can be no potential
difference between any.

Aluminium foil is a BAD idea. In the event that there is any appreciable charge
on a given pin, pushing it into aluminium foil will discharge it *quickly* and

And how would this occur?

Because the ali foil provides essentially a short circuit path.


the resulting current may kill it.

Always use high resistance material for storing ICs like the anyi-static black
foam material. This allows any charge to 'leak' away slowly and safely.

Aluminum foil is fine. The black stuff has a relatively low resistance
anyhow. Check it with an ohmmeter.

I have many times. You're plain wrong or using the wrong grade foam.

Graham

On Fri, 23 May 2008 01:05:05 +0100, Eeyore
wrote:

....snip.....

Aluminium foil is a BAD idea. In the event that there is any appreciable charge
on a given pin, pushing it into aluminium foil will discharge it *quickly* and

And how would this occur?

Because the ali foil provides essentially a short circuit path.


the resulting current may kill it.

Always use high resistance material for storing ICs like the anyi-static black
foam material. This allows any charge to 'leak' away slowly and safely.

Aluminum foil is fine. The black stuff has a relatively low resistance
anyhow. Check it with an ohmmeter.


The safer practice nowadays is to use high resistance materials,
and NOT aluminum foil, or metal film covered plastics, or that black
conductive foam. The low resistance materials allow fast and high
charge/discharge currents that can vapourize small tracks or
microcircuitry. You should notice that a lot of packaging now uses
those pink bags, and if you check with an ohmmeter, they appear to
have an extremely high resistance. That allows voltages to dissipate
with low (less damaging) current.
The low resistance stuff is used to protect against external
electric fields. If you have both situations, then put the component
in a disipative bag (pink, high resistance), and then put that inside
a conductive pouch, say aluminum foil.
I'm told that you can effectively use the stuff that women commonly
use to control static on their dress clothes. It's a spray can, I
believe the active ingredient is sodium stearate (tallow?). It doesn't
last forever, but for weeks or months it's not bad. There are
commercial products that do a much better job, but you probably won't
find them at your supermarket. It provides a dissipative ilm, and will
not shield against electric fields.
Some of the little plastic boxes are quite evil when it comes to
voltage build up. You can flex one of those boxes, and easily build up
a charge of 200v-2Kv on the inside surface. That charge can induce a
a charge (and voltage) on a pin of a chip inside the box. I hade an
old analog voltmeter with a pastic face, I rubbed the face, and the
meter shifted about 10% because of the induced charge. One year later,
it was still off by 5%. By opening it up and breathing on the inside
plastic, I was able to eliminate the problem. I was really surprised
at how long that charge was held!
The statistics of ESD (Electro static discharge) suggest that the
probability is quite high that no apparent damage will show up right
away, but the component will be stressed, and will not live out its
normal design lifetime. ESD problems are one of the biggest cause of
poor reliability of microcircuitry.
Check this site: http://www.esda.org

-Paul