The victim (I snapped the pins off since they are easy to remove and had more of an impact of nitric reactions):
Initial setup:
I didn't take a picture of this, but the solution started to turn brown and diffuse out around the IC before too long. Began to turn darker:
And eventually black:
The acid behaved differently in the 555 flask (misty, no creeping along sides in 555 vs creeping and no mist):
After draining and some initial acetone rinse:
The die is seen in the leftmost object. I've been told that sulphuric is useful for live decapsulation and it certainly shows here. Much of the "wiring" was preserved despite prolonged exposure to acid. Nitric on the other hand would have obliterated these. Not as visible, but also all of the bond wires were preserved.Since they were both analog ICs made by ST, it less likely that they were different epoxies. Both used fresh acid. Probably due to some contamination in the flasks.
I'll try to update with some IC pictures. Nitric tends to leave a lot of residue. This on the other hand had overall clean dies, although one of them had sort of a grainy appearance, maybe from certain residues? Apparently the 555 didn't have a passivation layer and the 741 did which resulted in scratches on the 555 after I was careless during plucking and didn't realize it wasn't protected.
In summary, this is what I thought
Advantages
-Less fumes than nitric acid, MIGHT be safer with less equipment / ventilation. With the cover on my glassware and the top being somewhat cold from the environmental temperature, it seemed to reflux the acid and I didn't even really notice the fumes. Contrast with nitric where fumes are an inherent problem from the nitrate decomposition.
-Inexpensive
-Readily availible materials? Battery acid and drain cleaner are readily availible. Battery acid tends to be purer and would likely need to be distilled first, but drain cleaner (ex: Bull Dozer) is much stronger but with contaminants. In any case, generally not a controlled substance and one should be able to order it without too much trouble.
Disadvantages
-Higher working temperature. Might literally take your hand fall off if you spilled on it. When I was younger a single drop of cold concentrated sulphuric landed on my hand and caused a severe burn to which I'm reminded to this day by a scar. I can't imagine what a broken boiling beaker could do.
-From the solution turning black and the lack of bubbles, no clear indication of when its "done." Combined with the larger cool down time of the acid and glassware, this can make it inefficient for doing small batches.
Overall, probably a good compromise for those that want to try some of this stuff
-Grainy appearance on dies? Need to look more into what that came from
With this in mind, one good application might be to use it as a wash after nitric. Since I've found issues with particulate residues after nitric, a brief sulphuric bath might be able to clear them off. I think sulphuric works at lower (ie room) temperatures, albeit much slower, so it might not even require heating. I'll probably try to soak a fully encapsulated IC overnight and see how it goes as a starter.
Hi,
ReplyDeleteso far I had only limited success with conc. (96%) sulfuric acid.
Like you, I threw a few chips into a beaker with the acid. I heated it up and at about 90°C the acid started to turn black (i.e. it started to etch away the epoxy).
However, I was only successful with one chip. All others (especially the DIP packages in which I also milled a small cavity to reduce the amount of epoxy over the die) were not affected very much.
I suppose that's because the epoxy composition is different for chips from different manufacturers.
Since we're working with very similar acid concentrations, I would be interrested to which temperature you heated up the solution.
I was reading that for decapsulation with sulfuric acid, the acid is usually heated up to 225-250°C (boiling point is 337°C).
What I would like to do is to drop the acid into the milled cavity on the chip package, so that the rest of the package is being conserved.
Did you also try fuming sulfuric acid ?
I would also have lower concentrations of nitric acid (53%).
However, so far I did not make any experiments involving heating up or mixing the acid, as my fume hood has not arrived yet and the NoX gases that can occur with nitric acid are pretty dangerous.
Did you already experiment with that (i.e. a mixture of sulfuric and nitric acid) ?
Did you try hot nitric acid ? Which concentrations ?
cheers,
Stefan
I have a post on more advanced H2SO4 techniques that I started to write before you posted but haven't got a chance to push out, I think you'll really like it.
ReplyDeleteI've actually had very good results with H2SO4. I shoot for 150 - 160 C. It seems to work on almost all of the epoxies/chips I've tried so far with only one exception. Unfortunately I don't know who made it as it was part of a lot of chips I was never going to do anything with and didn't want to take the time to track them. Above this temperature fumes seem to increase a lot and I'm not sure if I gain a lot. So, ~150 has seemed to be a pretty good compromise between speed, safety, and results. What brand chips are you using? I have some good pictures of epoxies vs how hard they are to etch, I'll see if I can post them somewhere in near future. Basically, higher acid epoxy vs glass content means much harder to etch. If its too high it will form a hard sediment rather than dissolve. I have not tried oleum as I have not seen a need for it.
One of the reasons why I've moved away from nitric is that it corrodes aluminium at lower concentrations where as H2SO4 is slow enough that you often don't notice.
I use a 3M industrial respirator with acid gas cartridges to help with fumes (3M 7800, http://intruded.net:8080/siliconpr0n/lib/exe/fetch.php?cache=&media=hf_gas_mask.jpg) and do things outside. I also use watch glasses to cover beakers which reflows and considerably reduces fumes. I'm working on assembling or buying a fume hood but neither has gone through yet.
I I've experimented a little with nitric/sulfuric but not real need for it. I've heard its useful for passivating (or at least helping) copper corrosion when using nitric, but I've found straight sulphuric good enough that it hasn't been necessary. You'll be limited by HNO3's decomposition point. H2SO4 won't work once contaminated by the excess water, so its really only good for assisting HNO3.
Consider joining my wiki (just moved to http://intruded.net:8080/siliconpr0n/doku.php?id=start) if you have an interest in this stuff! I'd love more contributions / collaboration including things that you tried and didn't work. e-mail me at <@> for an account.
e-mail is johndmcmaster at gmail dot com.
ReplyDelete