pic microcontroller discussion list <> wrote on Friday, June 27, 2003 10:16
AM:

> For several years, one client had need for a 28Mhz PIC (14.31818 x 2
> ) for a video retrace job. I set up a test jig so he could cull the
> PICs that couldn't pass muster. After a few weeks he dropped the
> test. None ever failed. Thats about 40% overspeed.

The short answer is that they go as fast as you are happy to sell!  Nothing
is guaranteed by the manufacturer if you go outside the specifications, so
you effectively take on the responsibility for handling failures and their
consequences.  When there is no alternative, we qualify some commercial
components (for the avoidance of doubt, I'm not talking about PICs here!)
and test the resulting products extensively, to ridiculously high
temperatures, so that we can confidently use them at less ridiculous
temperatures (often well over 150 deg C).

If I asked the manufacturer of the devices, they would, quite rightly, say
that the parts would not run within specification at the required
temperature and if someone at A.N.Other Semiconductor makes a process
optimisation which increases their yield by 0.01% and all our tests fail,
that's just tough.  It's not their fault, and we have to find a suitable
replacement.  The same would go for overclocking etc.

In a previous job, I came across a company who were putting electronics,
with standard DIL packages in oil-filled hoses and taking them a couple of
km under the sea (for control of unmanned underwater vehicles, a
non-pressurised oil-filled container is much lighter, smaller and cheaper
than a thick metal enclosure).  They had the same situation, some DIL
packages had small air pockets, and the whole device could implode at
pressure.  Others would run satisfactorily at over 100x atmospheric
pressure.  The semiconductor manufacturer would not be interested in
reducing the number or size of bubbles in the package, if the company
wanted to use them, they had to test them.

However, if a part is available which meets the specs, then it is usually
the best choice, qualification testing is not trivial.

As a starting point, in my personal experience, overvoltage or overcurrent
are not good roads to go down, all other specs are open to testing if the
application requires.

Nigel
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