Information Security
deletion flash-memory
Updated Mon, 30 May 2022 02:23:16 GMT

Which temperature ensures permanent erasure of data on flash?


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.




Solution

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.





Comments (1)

  • +0 – Thanks! I took 80°C from some unrelated, random specification as a safe upper limit for storage (e.g., 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! — Nov 17, 2021 at 22:23  


External Links

External links referenced by this document: