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From: hogan@rosevax.UUCP (Andy Hogan)
Newsgroups: net.micro.mac
Subject: Re: RAM ugrades (static damage)
Message-ID: <233@rosevax.UUCP>
Date: Wed, 6-Nov-85 18:03:39 EST
Article-I.D.: rosevax.233
Posted: Wed Nov  6 18:03:39 1985
Date-Received: Sun, 10-Nov-85 09:51:47 EST
References: <1058@decwrl.UUCP> <27800002@ada-uts.UUCP>
Organization: Rosemount Inc., Eden Prairie, MN
Lines: 41


>>   5) RAM chips are easily damaged by static, and most users don't know
>>      how to properly ground themselves, the memory board, and the RAM
>>      chips while installing the chips.
>
>I personally think this static business gets blown out of proportion.
>I've handled A LOT of 256k DRAMs without blowing ONE, and I don't take
>any elaborate precautions - I just don't do anything blatantly stupid
>(like work in a polyester shirt under a wool sweater).

There is a widespread but completely mistaken understanding of ESD (static)
damage to integrated circuits which says it is an all-or-nothing proposition.
You can cause significant damage to an IC by static without "blowing" it
completely.  This damage takes the form of altered dynamic or static electrical
performance (ie, input current, output current, i/o impedance, speed, etc.)
and fairly often does not IMMEDIATELY affect the operation of the circuit.
However, such damage has been shown to significantly shorten the useful
lifetime of the IC.  So it is impossible to tell, immediately after installing
an IC in a circuit, whether it has been damaged by ESD or not.

Also, the word "easily" in the first post is a relative term.  256K RAMs are
indeed "easily" damaged with respect to certain other technologies, such as
small-scale TTL chips.  TTL is not destroyed by static until the applied
charge comes from a source of a few kilovolts, whereas a CMOS RAM can be 
utterly destroyed by a source of less than one KV.  Damaged-but-not-destroyed
levels show roughly the same magnitude difference.  Any system which 
prevents the buildup of a static field lower than damage levels is sufficient.

The choice of prevention measures is an economic one.  For one person, with 
one machine, careful handling, humidification and wearing cotton clothes may 
be enough.  For more than one, you have to make a judgement.  We tend to 
install our own (cheap) chips in PCs here because we have workstations that are 
available for such occasional use and that are fully protected, but this
equipment is moderately expensive, and I doubt we would buy much of it just
for our PCs.  However, good grounding wrist straps can be had for $15--20 and
that cost is easily justified.  

-- 
Andy Hogan   Rosemount, Inc.   Mpls MN
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