[vcf-midatlantic] X-ray erasure of EPROMs, was Re: Getting Data off old Atari Floppies

[Jonathan Gevaryahu]

On 12/14/2015 7:14 PM, Dave McGuire via vcf-midatlantic wrote:
> On 12/14/2015 07:11 PM, Jonathan Gevaryahu via vcf-midatlantic wrote:
>> Yeah 300F was completely wrong, I was mixing baking floppies up with
>> baking EPROMS after x-ray (not UV!) based erasure (which really does
>> need 300F).
>    Can you tell me more about this?  Does baking somehow address the
> problem of surface state creation during X-ray erasure?
>
>    (I type this with a glance at a stack of trays containing several
> thousand non-windowed EPROM-based microcontrollers, and another glance
> over at my X-ray machine..)
>
>              -Dave
>
All I can tell you about this is what I read from wikipedia's "EPROM" 
article and some articles on history of EPROM/intel 1702 stuff:
"

Erasure can also be accomplished with X-rays 
<https://en.wikipedia.org/wiki/X-ray>:

    Erasure, however, has to be accomplished by non-electrical methods,
    since the gate electrode is not accessible electrically. Shining
    ultraviolet light on any part of an unpackaged device causes a
    photocurrent to flow from the floating gate back to the silicon
    substrate, thereby discharging the gate to its initial, uncharged
    condition (photoelectric effect
    <https://en.wikipedia.org/wiki/Photoelectric_effect>). This method
    of erasure allows complete testing and correction of a complex
    memory array before the package is finally sealed. Once the package
    is sealed, information can still be erased by exposing it to X
    radiation in excess of 5*10^4 rads
    <https://en.wikipedia.org/wiki/Rad_%28unit%29>,^[a]
    <https://en.wikipedia.org/wiki/EPROM#cite_note-6> a dose which is
    easily attained with commercial X-ray generators.^[6]
    <https://en.wikipedia.org/wiki/EPROM#cite_note-7>

    In other words, to erase your EPROM, you would first have to X-ray
    it and then put it in an oven at about 600 degrees Celsius (to
    anneal semiconductor alterations caused by the X-rays). The effects
    of this process on the reliability of the part would have required
    extensive testing so they decided on the window instead.^[7]
    <https://en.wikipedia.org/wiki/EPROM#cite_note-jmargolin_com-eprom-8>

"

Also, 600C(1100F) is a fair bit higher than what I remembered from last 
time I read this.

Maybe try it with one less-desirable microcontroller and the X-ray 
generator? And bake it at various temperatures and see if it 'recovers'?

-- 
Jonathan Gevaryahu
jgevaryahu at gmail.com
jgevaryahu at hotmail.com