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<wpwrak>
azonenberg: btw, with your chip disassembly procedures, could you strip a chip (e.g., an FPGA) to the point where it would still work but where you'd have little enough material between the silicon and the outside that you could obtain meaningful chip temperature measurements
<wpwrak>
e.g., to characterize the maximum heat dissipation ?
<wpwrak>
(assuming that this is an input/constraint for synthesis)
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<azonenberg>
wpwrak: You can remove the epoxy entirely using HNO3 and leave bond wires intact
<azonenberg>
then do IR temp measurements
<wpwrak>
(assumption: if you measure through the entire package, things will already be too diffuse to be able to tell if there are dangerous hot spots)
<wpwrak>
so your process is precise enough to do this ?
<azonenberg>
Using nitric acid, yes
<azonenberg>
these days i've been mostly doing sulfuric which is less precise but cheaper and easier to get
<wpwrak>
ah, i see. it's all in the acid then ;)
<azonenberg>
sulfuric reacts slowly so you have to heat it a lot and just soak it in the tank for like half an hour or so
<azonenberg>
nitric is much faster and more aggressive but if done right you can control it pretty precisely
<azonenberg>
if all you wnat is a bare die then sulfuric is fine
<azonenberg>
that's what a chip done using nitric looks like if prepared skillfully
<wpwrak>
that looks pretty great
<wpwrak>
point-etching into the package adds a nice touch, too ;-)
<azonenberg>
We drilled it first to a little above the die and then put the acid in the well
<azonenberg>
makes for a much cleaner decap and less risk of damaging the leadframe
<wpwrak>
nice :)
<azonenberg>
oh, and a lot faster too
<azonenberg>
less stuff to etch
<wpwrak>
does the acid heat up a lot ?
<azonenberg>
You have to heat it or it wont etch at any appreciable rate
<azonenberg>
normally you run the decap at 150C ish
<wpwrak>
ah :)
<azonenberg>
red fuming nitric can decap at room temp if you let it sit overnight
<azonenberg>
lower concentrations absolutely must be heated, as with sulfuric
<wpwrak>
once had some fun with HCl+H2O2. made a very peroxide-rich mix. the pcb was etched in mere seconds, but the process wasn't exactly running at room temperature :)
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<azonenberg>
lo,l
<azonenberg>
I use 1 part HCl to 6 parts 3% H2O2
<azonenberg>
at ~80C for aggressive etch or slghtly above room temp for controllable
<wpwrak>
i don't have any friendly heating equipment, so i prefer processes that work at room temperature. and that ...erm, self-heating experiment was with a good quantity of 35% peroxide :)
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<azonenberg>
lol
<azonenberg>
35%? Ok, lol
<azonenberg>
RCA-2 is 1 part conc HCl, one part 30% H2O2
<azonenberg>
... and 6 parts water to slow down the reaction to sane rates :P
<wpwrak>
yeah, that was roughly my mix, just with a less cowardly quantity of water :)
<wpwrak>
i think there was also a bit of 5% peroxide in there, so it wasn't *that* nasty. but still. definitely not a process that would need 20 minutes for anything.
<azonenberg>
Lol
<azonenberg>
I note also that RCA-2 is meant for *stripping* metal (when used at 85C that is)
<azonenberg>
Not for controlled etching
<azonenberg>
It works reasonably well for PCBs at a less elevated temperature
<wpwrak>
"Solution will bubble vigorously after 12 minutes, indicating that it is ready for use."
<wpwrak>
at least they didn't write "impatiently" :)
<azonenberg>
for wet etching IC-level features I normally use ten parts water to one part of RCA-2
<wpwrak>
s/12/1-2/
<azonenberg>
etch rate of that is a few hundred nm per minute i believe
<wpwrak>
more than sufficient for such fine structures
<azonenberg>
Yeah, and more importantly somewhat controllable
<azonenberg>
lol
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<Fallenou>
mwalle I fixed my toolchain with correct CSR numbers and now all MMU unit tests are passing perfectly OK :)
<Fallenou>
thanks for the pointer !
<GitHub192>
[lm32-binutils-mmu] fallen pushed 1 new commit to master: http://git.io/HiQKDg
<GitHub192>
lm32-binutils-mmu/master 0dcd80f Yann Sionneau: Update lm32 toolchain with new refactored lm32 MMU
<Fallenou>
toolchain is now updated on github as well :)
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