Sorry for the late reply - been out of town...

I work for KLA-TENCOR.  Wafer, Reticle, Photomask, Metrology (deposition
thickness) and SEM inspection eqipment is what we are all about!  We
call it yield management technology...

Sorry for the above plug, but I just couldn't help it when I returned
this morning and saw this thread over the weekend.  It's a little off
topic, but for any of you interested (John P., et. al), in all of the
inspection steps involved in manufacturing an IC, our web sight will
prove interesting...

Point you browser to http://www.kla.com to find out what a manufacture
of chips (Microchip) needs to address in creating higher yield wafers...
Yield is everything in this business...

I'm not selling anything here - just trying to be informative to the
list.  The manufacturing of a wafer is a highly interesting topic....
Check out what it takes these days!

Cheers,

Chuck Mauro

> -----Original Message-----
> From: John Payson [SMTP:supercat@MCS.NET]
> Sent: Saturday, February 07, 1998 7:11 PM
> To:   PICLIST@MITVMA.MIT.EDU
> Subject:      Re: ??? high temperature PIC ???
>
> > I guess I ought to know this but I never really found out: do
> companies
> > making regular commercial grade components usually test each
> component in
> > some way??! I never exepected that, I always thought that components
> for
> > non-critical applications (i.e. consumer electronics) were only spot
> > checked. I could understand maybe testing each one of the industrial
> or
> > aerospace/military versions for saftey's sake (although, you would
> also
> > expect the final equipment manufacturer to test each final device
> under
> > these circumstances).
>
> In many cases, testing individual devices merely to see if they meet
> cust-
> omer specifications is not terribly useful; a crate of devices that
> happen
> to "barely" meet specs may turn into half a crate of devices that fail
> in
> use.  Instead, it's desirable to determine what types of defects or
> modes
> of failure exist, and then to work at identifying/preventing those.
>
> My impression of normal silicon manufacturing processes is that
> devices are
> at minimum somehow checked to ensure that no stray dust particle has
> prod-
> uced a crater or mountain somewhere.  While chips are always made in
> clean
> room conditions, even a room with one particle for every thousand
> liters of
> air will have a few dust particles that may land somewhere and wreak
> havoc
> on one chip on one wafer without affecting anything else; even if
> 99.99% of
> parts don't have such defects, most customers would like another nine
> at
> the end of that.
>
> For (E)PROM devices, my impression is that many such devices, even
> OTPROM's,
> are indeed programmed and tested before packaging; until the wafer has
> been
> sealed in the expoxy, there's nothing to prevent its erasure.  If the
> dev-
> ices program and operate correctly at various extremes of temperature
> and
> radiation exposure, they are very unlikely to fail in the field; my
> imp-
> ression is that all shipped Microchip EPROM-related products are
> tested for
> data retention at moderately high temperatures, and that some
> "sacrificial"
> units from each batch are tested at excessive temperatures.
>
> Once devices have been tested on the wafer, they are placed into
> either plas-
> tic of ceramic packages.  My impression is that when Microchip says
> that the
> JW parts are characterized but not tested at extreme temperatures,
> what they
> mean is:
>
> (1) All their parts are tested at temperatures somewhat outside the
> operating
>     range specification; the sacrificial parts are tested outside the
> "absol-
>     ute" specification.  The wafers themselves do not fail under such
> abuse.
>
> (2) The plastic-cased parts will suffer package-related failure at
> temperature
>     extremes which the ceramic cases can survive.  Microchip does not,
> how-
>     ever, test individual parts to ensure full-range temperature
> reliability
>     after they are packaged.  While Microchip does not expect /JW
> packages to
>     fail due to temperature extremes, it is possible that, e.g.,
> thermal exp-
>     ansion and contraction could weaken one of the die bonds.
>
> (3) Exposing individual parts to temperature extremes significantly
> outside
>     rated specifications may degrade their long-term reliability.  It
> would
>     not make sense for Microchip to take years off the lives of their
> parts
>     by exposing them all to extreme temperatures even if they'd found
> that
>     most parts treated that way would suffer little if any apparent
> damage.
>
> Note that these are only my impressions; since I don't work at
> Microchip
> anything above may or may not be right, and should be taken with 4
> grains
> of salt and 2 grains of oregano.