> Date: Wed, 9 Jun 1999 13:26:21 +1000
> From: Ben Hood <[EMAIL PROTECTED]>
> Subject: Re: CD-ROM and Modem
> Before handling CMOS chips, it is *recommended* to be static-free.
> But a lot of chips can't really be harmed much by static.
A qualified yes/no to that. First, CMOS circuits are generally protected
( and have been, since I first used them in 1971 ) via an input diode,
built in expressly for that purpose.
The only folks who MIGHT have a worry about handling them at all are
those in cold, dry climates where you can occasionally build up a multi-
thousand-volt "hand zapper" charge that lights up your life touching a
doorknob or appliance. ( The HV can avalanche the diode.)
The stuff to worry about is ( non-complementary-symmetry ) "plain old"
MOS, where a non-perceptible 90v charge can punch through the oxide,
destroying the thing. Usually, these are supplied with all the leads
shorted together ( a wire loop for transistors, foil or conductive foam
for ICs ) and the "short" is removed AFTER the device is installed in
the circuit. Once in-circuit, other devices on the board should limit
the destructive potential of low-level charges. That is why no one
should "fear" destroying a computer card via static, even if handled with
no static-protection devices or methods at all. ( Different story if
you've got so much of a charge that your hairs jump away from each
other ! )
> Whenever I handle these chips I just grab hold of the computer's
> chassis with it still plugged in, so its grounded through the power
> point.
Excellent, LIFE-SAVING advice where line voltages are concerned - provided
that only ONE hand is used. Could be FATAL using two hands. Put the
other hand in your pocket when doing this, and lay your forearm against
the chassis. There is no need to have a "real" earth ground connection;
the unplugged chassis will do just fine for preventing static damage.
One caveat, though: SIMM memory cards are relatively unprotected from
static damage; there often is nothing on these boards but memory chips.
Possible damage can be minimized by wrapping them tightly in aluminum
foil upon removal/storage/transport. Never just chuck them in a drawer,
box, or piled on a shelf.
Other than that, you are unlikely to harm your precious PC's circuits
via static charge ( unless you handle them with no precautions, after
walking across a nylon-pile carpet in a cold, very dry room!).
- John T. ( electronics tech/engr since 1968 )
-- Arachne V1.5a;alpha, NON-COMMERCIAL copy, http://home.arachne.cz/
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