albaugh@dms.UUCP (Mike Albaugh) (10/12/89)
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? I'd ask the vendor, but I'm pretty sure the answer would be: "Hey, cheapskate, buy new ones" :-), and Enquiring minds want to know! (and I _am_ a cheapskate, so what...) I have to assume that they test these puppies somehow, and a complete test at wafer-probe sounds unlikely to me. So, should I run them through an airport security machine, get friendly with my dentist's X-ray technician, find a good deal on a used Therac ( 1/2 :-) ) or maybe just nestle them in next to the 1B3 in my old TV :-) Any Suggestions? I'll take email and post a summary if I get a usable suggestion. Mike | Mike Albaugh (albaugh@dms.UUCP || {...decwrl!pyramid!}weitek!dms!albaugh) | Atari Games Corp (Arcade Games, no relation to the makers of the ST) | 675 Sycamore Dr. Milpitas, CA 95035 voice: (408)434-1709 | The opinions expressed are my own (Boy, are they ever)
davidc@vlsisj.VLSI.COM (David Chapman) (10/13/89)
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? You'd better believe they test the whole thing with wafer probing. No semiconductor company worth its salt would ship partially-tested chips. Of course, before they're packaged the company can simply zap 'em in the tanning booth. In theory, the chips should also be tested after packaging (there is some loss - wires break, etc.). I think they could be erased after testing with X-rays. I quote my semiconductor materials textbook ("Device Electronics for Integrated Circuits", Richard S. Muller & Theodore I. Kamins, p. 452): The buried polysilicon layer in a FAMOS device retains the charge on the gate for any practical time period unless some source of external energy is able to liberate the electrons held there. A suitable energy source to excite them is photon irradiation which can give the electrons sufficient energy to pass over the barrier at the interface between the polysilicon layer and the oxide. As long as the plastic package is transparent to X-rays, you should be able to do it. So why do people buy these things in the first place? My guess is that the package simply costs less and so they're cheaper for people who aren't going to change the programming very often. Of course, there is a fair market for ROMs; OTP EPROMs are a pretty easy way of making ROMs without the masking expense or difficulty of changing the code. We at VLSI have stopped making larger ROMs (1Mbits is as large as we go) because no one is willing to commit to freezing code enough to make them in volume. They all worry about patches, bug fixes, etc. Think about it - 128 Kbytes is a lot of code! > Any Suggestions? I'll take email and post a summary if I get >a usable suggestion. E-mail doesn't seem to work well for me; sorry. A lot of stuff I send just bounces three days later. -- David Chapman {known world}!decwrl!vlsisj!fndry!davidc vlsisj!fndry!davidc@decwrl.dec.com
jones@bach (Clark Jones) (10/14/89)
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!
mmm@cup.portal.com (Mark Robert Thorson) (10/16/89)
davidc@vlsisj.VLSI.COM (David Chapman) says: > You'd better believe they test the whole thing with wafer probing. No > semiconductor company worth its salt would ship partially-tested chips. That's true when such testing is possible. FPLA's and PAL's, however, must be shipped with only partial testing because the fusemap can't be tested without burning it.
mmm@cup.portal.com (Mark Robert Thorson) (10/16/89)
jones@bach (Clark Jones) says: > 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 I find this a little hard to believe. I recall reading about x-ray erasure of plastic-encapsulated EPROM's in an old Intel memory design handbook, and I believe the figure they quoted was 100 rads.
phil@diablo.amd.com (Phil Ngai) (10/17/89)
In article <23127@cup.portal.com> mmm@cup.portal.com (Mark Robert Thorson) writes: |davidc@vlsisj.VLSI.COM (David Chapman) says: |> You'd better believe they test the whole thing with wafer probing. No |> semiconductor company worth its salt would ship partially-tested chips. | |That's true when such testing is possible. FPLA's and PAL's, however, must |be shipped with only partial testing because the fusemap can't be tested |without burning it. To pick a nit, there are plenty of UV and EE PALs now. More seriously, I have burned plenty of PALs and never had a failure to program. I don't know how the testing works but the bottom line is the products are very reliable. -- Phil Ngai, phil@diablo.amd.com {uunet,decwrl,ucbvax}!amdcad!phil Just say NO to the "War on Drugs".
davidc@vlsisj.VLSI.COM (David Chapman) (10/17/89)
In article <1989Oct13.232523.3999@sj.ate.slb.com> jones@bach.UUCP (Clark Jones) writes: <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? < <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. X-rays shouldn't be a problem; they're simply more energetic photons than the UV you normally use to erase an EPROM. Maybe you could call Intel (or any of the other EPROM vendors) and ask. -- David Chapman {known world}!decwrl!vlsisj!fndry!davidc vlsisj!fndry!davidc@decwrl.dec.com