15 Mar
1998
15 Mar
'98
9:14 p.m.
On Mar 15, 19:46, Thorhallur Ragnarsson wrote:
Subject: Re: Getting bent (ON topic if not thread)
[ plain text
Encoded with "quoted-printable" ] :
Hooray!
At 07:26 15.03.1998 PST, Max Eskin wrote:
>Actually, I find most precautions such as anti-static and so forth to
>be baloney.......
I've spent a lot of my working life repairing boards that have been blown up,
so I can't agree.
No, unfortunately this can be a real problem, some
years ago when working
as test engineer for DNG Electronics, we suddenly had skyrocketing failure
rates in assembly of equipment containing CMOS logic. Everybody involved
was grounded with a 1Mohm wrist strap so this was quite a mystery until we
noticed that when carrying the boards from the test bench to the final
assembly, the lead from the strap was too short and the carrier had to
disconnect it for the 6 feet trip across the floor, this zapped approx. 30%
of the boards. His shoes must have been something!!
That's quite a common effect. One of the big electronics companies published
some figures on it a ten years or so ago. Often, it may alter a device's
response to high frequencies as well. But I don't agree with those who say you
must never touch a chip, or must hold it by the ends without touching the pins.
If I have to carry an EPROM or similar without antistatic foam, I make a point
of ensuring that all the pins are touching my finger, on the grounds that my
slightly-conductive skin is keeping all the pins at the same potential.
...................... When I was upgrading RAM in
the machines in
my school's MacLab, the person in charge of it constantly looked over
my shoulder and bleated, "Touch the case again, Max. I want to SEE you
touch the case. OK, now gently, gently, now. Oooh! Yeesh! DON'T touch
those chips!",etc.etc. I didn't damage anything, ......
Well, we have no way of knowing that. Static damage may just weaken the
chips so they fail later. Yes, I hope we are lucky. I do not normally wear an
antistatic wrist strap,
I just try to wear cotton clothes, "touch the case" often and avoid rubbing
against all those synthetic surfaces (table, chair, carpet etc.).
When dealing with old equipment I try to be even more careful as it may be
more static sensitive and spares harder to find.
I once (mid-80s) had several calls from a school that had refitted a computer
room; machines kept crashing, usually at the start of a class. I only remember
one permanent fault, but when I eventually asked the right question, it turned
out they had a new carpet with a high nylon content. I suggested they spray
the carpet with very dilute carpet cleaner in one of those mister bottles that
plant lovers always seem to have, and to repeat that once a week or so. The
problems went, and never came back.
--
Pete Peter Turnbull
Dept. of Computer Science
University of York