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Which heat ensures permanent loss of data on flash memory, in particular, on consumer-grade USB thumb drives (e.g., http://www.amazon.de/dp/B085SXT9FS or http://www.hood.de/0094819941.htm )? How long should be the exposure to that temperature to erase, say, 50% of the data? Clearly, everything is gone at the melting point of the material (1410 °C for Si), but, perhaps, smaller temperatures above 80 °C would also work?

Note: I'm not asking for the safe storage or usage temperature (which is stated in a JEDEC specification), which is probably way below the temperature asked above. I'm also not asking for the temperature at which the memory cells regenerate.

GeekestGeek
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    Does this answer your question? [Have I properly destroyed my SSD?](https://security.stackexchange.com/questions/255136/have-i-properly-destroyed-my-ssd) I covered thermal degradation factors in my answer. – Polynomial Nov 17 '21 at 17:58
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    @Polynomial A linear extrapolation to high temperatures does not reflect the actual physical processes, because if it would, then, according to an answer there you would still have data left at any temperature, in partiuclar, at 1410°C. The degradation factor at 1410°C is (1410−82,5)×6+168 = 8133. In physical reality, it should be infinity because silicon melts at 1410°C. – GeekestGeek Nov 17 '21 at 18:30

2 Answers2

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No simple answer here.

Here is a non-exhaustive list of the modern-ish digital electronics failure modes.

  1. Temperatures below 120C are mostly safe even for prolonged exposure (like months). No, your 80C will not work. Boiling water doesn't work either, on more or less sane devices.

  2. Somewhat above this (~150..200C) plastic starts softening and tin starts melting, so whatever electronic device you heat that much becomes unusable because of physical disintegration (the integrated circuits will desolder and deform). The surface tension-induced deformation may tear off the tiny connections between the Si crystal and the external leads inside the chip, making the chips pretty much inaccessible without a piece of special chip-slicing equipment (and skills).

  3. Somewhat higher (~300C) the insulated gates of the flash memory will start leaking their charge rather quick (maybe minutes or even seconds for modern high-density memory). This will erase the flash memory making it all 0 or all 1 (depending on its controlling logic).

The wave or dip soldering happens in this temperature interval so short exposure (seconds) is still considered safe. Longer heating usually makes something stop working.

  1. Around the same temperature, silicon dopants that create P and N semiconductor types will diffuse on hours timescale, making the chip not only erased but circuit-less as well. 100C higher the same will happen for probably seconds.

It is up to you to declare the chip "erased" at some of these points.

devblack
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fraxinus
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  • Thanks! I took 80°C from some unrelated, random specification as a safe upper limit for storage (e.g., https://www.amazon.de/dp/B01M9988MV). So, it's not “my 80 °C”, and it is unrelated anyway. Anyhow, for me, the answer is your third item: 300°C. Thanks again! – GeekestGeek Nov 17 '21 at 22:23
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For non-destructive erasure, it's a matter of temperature versus time. NAND flash inherently loses charge over time, with the rate depending exponentially on storage temperature and on operating temperature when the data was written. Assuming the data was written at 35°C, a modern SSD stored at 55°C for two weeks will likely start seeing unrecoverable data loss, with further time needed for complete erasure.

It's probably more practical to go with either physical destruction or, if the device supports it, secure erasure. Even at 85°C, you're still looking at days of heating to erase it.

Mark
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  • Thanks and my question is more about USB thumb drives rather than proper SSDs. – GeekestGeek Nov 18 '21 at 23:22
  • @GeekestGeek, the only real differences between a thumb drive and a SSD are the shape and the interface. The storage chips are the same, as is the charge-loss rate. – Mark Nov 19 '21 at 00:22
  • Thx! As for the charge-loss rate, you say it. SSDs offer SMART capabilities, whereas USB drives don't. Consumer-grade SSDs are typically more reliable and prepared for long-term usage than consumer-grade USB thumb drives. The SSD technology differs: you have SLC, MLC, TLC, and heaven knows what there. – GeekestGeek Nov 20 '21 at 01:34