Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!tut.cis.ohio-state.edu!gem.mps.ohio-state.edu!ginosko!uunet!sjsca4!bach!jones
From: jones@bach (Clark Jones)
Newsgroups: sci.electronics
Subject: Re: OTP (really?) EPROMS
Keywords: EPROMS X-rays
Message-ID: <1989Oct13.232523.3999@sj.ate.slb.com>
Date: 13 Oct 89 23:25:23 GMT
References: <841@dms.UUCP>
Reply-To: jones@bach.UUCP (Clark Jones)
Distribution: usa
Organization: Schlumberger ATE, Tempe, AZ
Lines: 28

In article <841@dms.UUCP> albaugh@dms.UUCP (Mike Albaugh) writes:
>
>	Suppose for the sake of argument that somebody had access to
>a fair number of "One Time Programmable" EPROMS that were already
>programmed. Is there a way (like, f'rinstance X-rays) to erase them
>anyway? 

Many years ago, I heard of one chap in the UK who could not afford an EPROM
eraser, so he would mail his EPROMs, along with return postage, to his
friend in Belfast.  The EPROMs would return blank.  The tale speaks, if true,
(a) of the agressiveness of the x-ray equipment that the Royal Post Office
was using for screening packages and (b) the rather leakyness of the floating
gate insulation glass used at the time.  There have been great strides made
in the latter since the early '70's.  This can be seen by the lack of any
mention of either time or read-cycle limits to data retention in the data
books.

Personally, I wouldn't use an x-ray erased EPROM in any system where future
reliability was of _ANY_ consequence, such as in a game cartridge to be
sold.  However, if I had a bunch of the things, and they were in packages
other than "cer-dip" with the soldered-on lids, and had ready access to
an x-ray source _with appropriate shielding_, I might give it a try for
things such as providing more EPROMs for debugging cycles.  If the OTP
EPROMs were in "cer-dip" packages, I'd just pry off the lids and be
careful thereafter to not leave them out in the rain.  :-)

Disclaimer: The opinions expressed above are mine and not those of Schlumberger
because they are NOT covered by the patent agreement!