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

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". Most UV Eproms begin to erase when exposed to UV wavelengths shorter than 4000 A (Angstroms). I found the following statement concerning EPROM sensitivity to UV light on page 10-9 of the National Semiconductor 1984 "CMOS Databook" (and yes, I _am_ a packrat when it comes to old databooks :-) concerning the 27C16 (a very common older type of EPROM):

Erasure Characteristics: "... It should be noted that sunlight and certain types of fluorescent lamps have wavelengths in the 3000 A - 4000 A range. Data shows that constant exposure to room-level flourescent lighting could erase the typical NMC27C16 in approximately 3 Years, while it would take approximately 1 week to cause erasure when exposed to direct sunlight..." Also, one must keep in mind that the timeframes listed above are probably derived from studies of "freshly programmed" eproms. Most of the ones we would be interested in would already have a number of years of charge decay under their belts. I was unable to find a reference to a finite lifetime for UV Eproms, but I seem to vaguely recall that there is a limit (~10 Years? sounds short, but I seem to remember reading it somewhere. Does anyone have this number at hand?) The end result of all this is that if you have any equipment you consider valuable, and it has windowed EPROMS, make certain that the windows are covered with an opague sticker. You might also consider dumping their contents to a data file for archival purposes. (and possibly re-programming them to effectively "refresh" them). -al- -acorda(a)1bigred.com _______________________________________________ cctalk mailing list cctalk(a)classiccmp.org http://www.classiccmp.org/mailman/listinfo/cctalk