DOH!

[Martin Czech]

Sorry, I can't stay away from replying to that, cause fighting ESD
is part of my profession.


I don't know what tinfoil is (aluminium foil? or is it really tin?),
nevertheless, one should only use static dissipative material to prevent
ESD damage, NEVER metal.

The reason is that if you use static dissipative foam etc. you have
about 1e6 - 1e9 Ohm. This is enough to discharge safely with low currents
in a few seconds.

If you use pure metal sheets or the like (screwdriver!) you will also
have a discharge, but a very rapid one, in some 100ps or ns.  This means
very high currents, 1A -10A !. This appears when the device is charged
against the environment, which is the normal case today (your wear a wrist
strap).

In most cases the device is not killed by beeing charged to some high
potential (rember that potential is relative), it doesn't hurt if some
silicon chip is at 10000V above ground, as long as it is charged as
a whole.

But the device is killed due to internal voltages that result from the
discharge current and discharge current path (Ohm's law).

To avoid rapid discharge, the soldering iron, table matt, chair etc. should
all be connected to safe ground via resistors or via dissipative material.

(Some guys from Siemens HL (now Infineon) showed pretty lab results,
walking on carpet or just standing up from an unsafe chair could charge
a test person to more then 4kV in less then a second).

A steel table e.g. will make ESD worse, not better.

Still some people send semiconductors wrapped in aluminum foil,
or on nonconductive styro foam with a sheet of aluminum foil on it.
This means that these guys have no clue about what ESD is.
Styro foam is the worst case material, because it will charge up
rapidly due to friction. Sometimes it is really hard to get those
foam chips of your hands due to the coulomb forces.

A reasonable supplier uses only static dissipative tubes, or other kinds
of dissipative containers. You should avoid unsafe suppliers, because
it will cost you both, time and money to find out if parts are degraded
or destroyed due to unprofessional handling.

m.c.


:::Date: Fri, 5 May 2000 03:15:12 -0400 (EDT)
:::From: Paul Wilkinson <synthdiy at mail.com>
:::To: Synth synthdiy <synth-diy at node12b53.a2000.nl>
:::Subject: DOH!
:::Content-Transfer-Encoding: 7bit
:::X-Originating-IP: 63.193.120.159
:::
:::WAS going great, until I smoke-tested the filter.  I plugged in the 3140's
:::and then turned on the board.  No smoke, but the middle 3140 got hot.  Any
:::idea what could cause that?  Do I have a capacitor backwards again?
:::
:::I've been pretty careful with the 3140's, keeping myself grounded.  I press
:::a piece of tinfoil into the back of the socket while I plug them in.  Should
:::be enough, huh.  They didn't come in a static bag though, so I'm not sure
:::they were packed properly at Electronics Express.
:::
:::- Paul
:::
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