Bob Ammerman wrote:
>
> > Thanx everyone for your help!
> > It would benefit me to have a 12f508 on the market. I wouldnt have to
> bother
> > about UV erasing the thing and I would develop the code on the flash part
> > and then use an OTP part for the final device. Or I could just emulate the
> > code first, modify it, wack it on a 16f84, see if it works and then wack
> the
> > code on the OTP device. Hmmm I can hold my breath and wait/hope for a
> 12f508
> > or I can do the latter!
> >
> > Wouter: Just for the sake of it (ie: killing time), I'll try converting it
> > to a JW part tonight! If it works I'll put my entry in for the lotto! Will
> > exposing the internals of the chip wreck it, as in exposure to air?
> > The last method of yours is quite a good idea!
>
> Chips are encapsulated to protect them from damage caused by the slow
> infiltration of contaminants. If you manage to open up the chip without
> physically damaging the lead frame, bonding wires or die it will probably
> work, for a while at least.
>
> Anybody's guess on the definition of 'a while'.


Many (!) years ago our company's product used many fusible link PROMs.
Did I say it was a long time ago?. As is normal, the design changed and
these one-time-programmable parts became worthless. They of course were
still good. We removed the metal lid of one by filing it off. This left
the bond wires and die completely undamaged. Every once in a while we
would take the opened part and compare its program to an unopened part.
We did this for months and every time the part was still good. We must
have lost interest before the opened PROM failed because I don't
remember it ever going bad.

Because of our success with the PROM, we decided to open a CCD shift
register digital memory chip. Once the chip was open, we plugged it into
a system to see if it still worked. This chip was used in a TV image
memory so we were able to shine light on the chip and see changes in the
picture!

Next, we decided that we wanted to see the insides of a Motorola MC6800
microprocessor. Most of the parts we had were in plastic packages and
couldn't be opened. One of the engineers had a sample in his drawer that
he used as a test replacement when he suspected a bad microprocessor.
This part was in a metal lidded ceramic package. We convinced the owner
that he could no longer trust part since he had used it so much. :-)

We opened it up and passed it around for everyone to admire. After it
had been oohed and aahed over by many people, someone suggested that we
plug it into a circuit to see if it still worked. It didn't. :-(
It was pointed out that with all the handling that maybe one of the bond
wires had been damaged. So, one of the technicians looked at the part
under a stereo microscope. He saw 2 bond wires bent and shorted
together. He then proceeded to use a stripped 30ga. wire-wrap wire as a
crowbar to straighten out the damaged bond wires!

When we put the repaired chip back into the circuit it still didn't
work. :-(  But wait... It was exposed to the room lights. When we cast a
shadow over the die it DID work!

Is this a detailed enough answer for you Bob???


-- Rich




>
> Bob Ammerman
> RAm Systems
> (contract development of high performance, high function, low-level
> software)
>
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