[CCTALK] EPROM Life... Was: scanners & circuit boards...

From: Dwight K. Elvey <dwightk.elvey_at_amd.com>
Date: Thu May 16 15:55:13 2002

>From: "Corda Albert J DLVA" <CordaAJ_at_NSWC.NAVY.MIL>
>
>Now, I don't know the construction/nature of the tubes used
>in scanners, but I myself would be wary of photocopying or
>scanning a PC board with an unprotected (i.e. uncovered) EPROM
>window face-down on the scanning surface. My reasoning is
>as follows;
>
>Although a fluorescent tube in good condition shouldn't emit
>much UV, one has to remember the way such a bulb functions.
>The excited gas inside the tube emits almost entirely in the
>UV spectrum. This is converted to the visible spectrum by the
>phospor coating on the inside surface of the tube. Over time,
>I have seen some of the coating flake off the inside of old
>flourescent tubes, providing a bunch of small UV "windows".

 The fluorescent tubes used in offices usually have ordinary
glass and in plastic fixtures. I would suspect that the 3 year
period is rather pessimistic. Many scanners use halogen lamps.
These produce quite a bit of UV. Infact, a bare halogen lamp
can be used to erase EPROMs with a fan for cooling. It won't
be fast but it will erase. The glass plate in a scanner still
blocks much of the UV light that would cause damage. I wouldn't
think that running it through a scanner would remove more than
about a months worth of normal aging at most. Covering them
is simple and makes good sense. Still, it is a good idea to
store good data from EPROM's in a different form. I always
make both a *.BIN file and a printout of any of the EPROM's
and most of the ROM's that are in my older equipment. Cosmic
rays will eventually erase any EPROM is leakage doesn't do
it first.
 I have some 1702A's that were programmed over 20 years ago
that are working fine ( around 1972, almost 30 years ).

 On a side note, ceramic packaged parts will also scratch
glass.
Dwight
Received on Thu May 16 2002 - 15:55:13 BST