Before flash there was EPROM that couldn't be erased !
The first kit I sold was the Island Keyer which used a Motorola microcontroller IC, the MC68HC705J1a:
The J1a had the program stored in EPROM (Erasable Programmable Read Only Memory). Usually EPROMs had a ceramic package with a quartz window like this PIC12CE674 chip:
When developing the product the programmer would program the EPROM but then when it didn't work :) a UV light would be used to erase the program from the memory. Since the erasure took minutes (I forget exactly how many) usually the programmer would have at least two windowed parts so that one could be erasing while the other would be used in a circuit.
The much cheaper plastic production parts couldn't be erased though, unless the user had access to an x-ray machine ?
Unfortunately Motorola made the windowed parts "unobtainium" - the distributors like Digi-Key only had the plastic parts. Apparently when you are selling to Ford or some other big customer they didn't need the little customers.
But in my case Motorola actually did provide me with an erasable part:
This is a plastic J1a chip that I sent to a friend of mine who worked at Motorola in Illinois. He then had a friend who worked in the failure analysis lab. The process of removing the plastic above the die is called de-capsulization aka dcap. If it's done carefully the chip is still fully usable (although this one eventually died on me).
I remember that there were two ways we did this when I worked at GTE. One was rarely done using an instrument called a Plasmod. It had a couple of 6146 tubes and created a plasma using RF somehow that would get rid of the plastic.
But the more common method was to use red fuming Nitric acid to eat away the plastic. First a small bit of the plastic was removed from above the die using a Dremel tool (in a tiny drill press) to form a well. Then the chip was heated on a hot plate (within a ventilation hood). Finally the acid was put into the well and allowed to bubble. Then the acid and dissolved plastic was washed away (gently) to reveal the die.
I was surprised that the chips still worked but the fine gold wires and chip were unaffected by the acid.
Although it's called plastic the encapsulant is a highly engineered material available from just a handful of factories in Japan.
Eventually Motorola did provide the ceramic erasable versions of the J1a chip but I was able to use the dcap J1a to develop the Island Keyer.
Now microcontrollers use flash memory which is electrically erasable so EPROM is just a "fading memory" kinda like Motorola :)
Best Regards,
Chuck, WB9KZY
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