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!!
>
> >...................... 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.
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.
> 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
Received on Sun Mar 15 1998 - 21:14:32 GMT