ESD can cause device degradation long before actual failure. It is a
common fallacy to assume that because you aren't aware of any sparks
etc. that ESD is insignificant. In fact, ESD events which are
undetectable at the human level i.e you don't feel a jolt or see a
spark, can still cause device damage.

Protective diodes are not a panacea for ESD and you should take
precautions. If you don't wish to muck around with wrist straps, I have
found at least that working without shoes on will minimise static
buildup since the leather or synthetic soles of shoes are a major
contributor when rubbed across carpet. Of course, avoiding carpet is
also good.

Interestingly, the problem of ESD damage was first observed, not with
MOS devices, but with, of all things, precision metal-film resistors.
These were packaged in plastic bags and some lots, mysteriously, were
out of tolerance when installed. The problem was traced to ESD damage.
As I said, subtle degradation can occur long before complete device
failure.

> ----------
> From:         Reginald Neale[SMTP:neale@SERVTECH.COM]
> Reply To:     pic microcontroller discussion list
> Sent:         Sunday, December 07, 1997 3:35 PM
> To:   PICLIST@MITVMA.MIT.EDU
> Subject:      Re: mchp and esd?
>
> >Hi All.
> >
> >Is it *necessary* to use a ground strap when
> >experimenting with pic chips?
> >
> >TIA,
> >Ray
>
> Well, *necessary* probably isn't the right term. Are you launching a
> space
> probe or just mucking about with PICs on the workbench? There's a
> spectrum
> of tolerable risk. All in all, PICs are pretty rugged, at least as
> idiot-proof as most of the other chips you might be using. But they're
> not
> indestructible. If you shuffle across the rug and pick up your circuit
> board, all bets are off.
>
> A wrist strap, properly used, can help a lot. The best defense is
> understanding how ESD is generated and controlled.
>
> Reg Neale
>