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'OTP'
1998\03\11@181949 by Gavin Jackson

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I was just thinking, why don't they
make OTP packages out of some
UV transmissive plastic?

1998\03\11@202004 by Peter van Hoof

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-----Original Message-----
From: Gavin Jackson <spam_OUTvulcanTakeThisOuTspamIHUG.CO.NZ>
To: .....PICLISTKILLspamspam@spam@MITVMA.MIT.EDU <PICLISTspamKILLspamMITVMA.MIT.EDU>
Date: Wednesday, March 11, 1998 6:23 PM
Subject: OTP


>I was just thinking, why don't they
>make OTP packages out of some
>UV transmissive plastic?
>
or out of ceramic's with a quartz window in it and they could call it the
eprom version :}

Peter

1998\03\11@230249 by Eric Smith

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Gavin Jackson <.....vulcanKILLspamspam.....IHUG.CO.NZ> wrote:
> I was just thinking, why don't they make OTP packages out of some
> UV transmissive plastic?

OKI offered EPROMs in a plastic package with a UV-transmissive plastic window
about 15 years ago.  I'm not certain why the whole package wasn't made of
the UV-transmissive material, except that perhaps it was to brittle or
fragile.

However, exposure to the relatively intense UV necessary to erase the EPROM
would cloud the window (rendering it UV-opaque) after only a few erassures.
I suspect that they decided that there wasn't enough benefit to justify
the cost.

I never actually purchased any of those EPROMs, but years later I found
a board stuffed with about 50 of them.  I haven't tried to erase them.

At this late date, it would make much more sense for Microchip to switch
to a flash EEPROM technology rather than trying exotic packaging for
UV erasable devices.  Unfortunately it appears that Microchip only has
EEPROM technology using large FAMOS-type cells, rather than true modern
flash cells.  However, that doesn't stop their marketing department from
calling it "Enhanced Flash".  Presumably the large EEPROM cell size
explains why they don't use "Enhanced Flash" on all of their devices,
instead of EPROM.

Cheers,
Eric

1998\03\12@003156 by Mike Keitz

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On Thu, 12 Mar 1998 03:51:41 -0000 Eric Smith <EraseMEericspam_OUTspamTakeThisOuTBROUHAHA.COM> writes:
>Gavin Jackson <vulcanspamspam_OUTIHUG.CO.NZ> wrote:
>> I was just thinking, why don't they make OTP packages out of some
>> UV transmissive plastic?
>
>OKI offered EPROMs in a plastic package with a UV-transmissive plastic
>window
>about 15 years ago.  I'm not certain why the whole package wasn't made
>of
>the UV-transmissive material, except that perhaps it was to brittle or
>fragile.

There were some attempts at windowed plastic packages, but they didn't
work out, I suspect they didn't seal the chip away from dirt and water
very well either.  And of course they would cost more than a plain black
plastic package, which is what most people wanted: minimum cost.   The
cost to get an EPROM back from the field and erase it would be more than
buying a new one.

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1998\03\12@014748 by John Payson
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> I was just thinking, why don't they
> make OTP packages out of some
> UV transmissive plastic?

Fair question; it would seem that transparent plastic would be cheaper and
easier than those expensive ceramic/quartz packages the manufacturers use.
There are, however, a number of problems that would have to be solved to
make "transparent" devices practical.

[1] Many types of transparent plastics are either opaque to hard-UV light,
   or are degraded by it (they either become opaque or lose structural
   stability).

[2] An IC's package must be able to withstand very high thermal gradients
   at the leads while remaining gas-tight.

[3] For small quantity runs, it's cheaper to produce chips in ceramic than
   to tweak all the necessary parameters for encasement in plastic.  This
   is why prototype chips are almost invariably produced in ceramic pack-
   ages (windowed or not).

[4] There isn't a terribly high demand for EPROM-based micros in transpar-
   ent packages.  Unlike chips such as optical sensors and such which need
   to be in transparent packages to be useful, the total demand for many
   types of windowed EPROM processors is in the low thousands; in products
   that don't require UV-erasability, opacity would be a good thing even
   when it wasn't strictly necessary.

If someone were to produce a micro with a built-in 1000 element optical
sensor (bar-code scanners, anyone?) it may be practical to undergo the
expense of a semi-UV-transparent package for all the micros (since a trans-
parent enclosure would be needed to use the optical sensor).  Most likely in
such a case, though, the device would only be good for a few program/erase
cycles before the case was too badly damaged (if you were careful to avoid
excessive exposure you might get a dozen or two).  Absent a compelling rea-
son to make the mass-produced micros transparent, though, I doubt strongly
that any manufacturer is going to bother.

1998\03\12@052246 by m00c0600

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Gavin Jackson wrote:
>
> I was just thinking, why don't they
> make OTP packages out of some
> UV transmissive plastic?

Because then there would be no market for windowed chips :)
(amongst other reasons)
jim

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