Tuesday, November 30, 2010

Sulphuric acid decapsulation

Something I've been meaning to try for some time. Somewhat arbitrarily I decided to go analog, the victims were a 741 op amp and a 555 timer. The torture:
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
-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.
-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.
-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.

Monday, November 8, 2010

Back to Troy, NY

After spending the summer in Cambridge, MA and back to SF Bay area for a few weeks, I've been back to Troy, NY. What makes Troy special? I'll tell you...
Luxurious homes
Expensive cars
Booming industry
And fine art
Okay, so its not quite as bad as I make it look, but most of these were taken pretty close to my apartment. To be fair, they've been knocking down a lot of the old buildings and graffiti is pretty rare except when this construction wall went up at RPI and people went nuts. I'll omit those pictures as if the first pictures don't get me hate mail, I get the feeling RPI might give me a "strong suggestion" to take down the latter.
Now that the small talk is out of the way, on to business. Although I haven't been posting anything, a lot has been happening. First, the microscope I previously mentioned never came, but eBay refunded me. However, my room-mate bought a metallurgical microscope with USB camera, so I'm better off than ever. Being off campus now, I also have less restrictions and don't have to deal with RA BS and such. One perk of my apartment is that I got some lab space in an area that's being remodelled. Its going to go away in January, but I'm hopefully moving out then anyway, so that shouldn't really effect me. The end effect of this is that I'm finally getting a chance to do all of the stuff I wanted to before and actually have some time and space to try things out.
I've imaged a bunch more IC pictures. In particular, I have images of discrete transistors, fully delayered 7404 hex-inverter, and other ICs.
3906 top metal
Old TMS320 logo section
On that note, a die image archive was started at http://intruded.net:8080/wiki/ Since I like Wiki's, I got myself an account and you should expect to see any die images I publicly release to appear there. I posted a few from a bit back, but haven't gone on a rampage yet. One of the things they are working on is getting a "Google Maps" style IC viewer for larger ICs. A crude test page is at http://intruded.net:8080/map/ (you'll have to zoom to correct level).
Map view test for large ICs
Regarding http://siliconpr0n.wikispaces.com/, I recently got permission from Sergei P. Skorobogatov to include images from his Semi Invasive Attacks paper on the Wiki as long as they are credited to him. So, along with the other material I've been accumulating from my own research, expect some rapid expansion on the Wiki in the near future.
After delayering a few 7400 series ICs, I've realized I had in fact been at the transistor layer before, but just didn't understand what I was looking at. Probably bad been confused by all of the MOS pictures I had seen? In any case, I tried a 74163, but found it was too complex to start with. I could only recognize a handful of components. A few days ago I delayered a 7404 which should provide a much cleaner reference circuit since its small and more or less split into 6 regular units. Unfortunately, I let it sit for a while without agitating it, so it crystallized a bit, but should be fine for my purposes.
7404 transistors
A quick overview of the techniques I currently use and why. Most ICs are in epoxy. I boil them in 70% nitric until the epoxy is removed. Lacking an ultrsonic cleaner, I wash them in room temp 3% HF for about a minute to clean the surface. This takes a thin layer off the top, which removes most debris. Then, depending on how patient I'm feeling, either room temperature or near boiling 3% HF to delayer the IC. If I want to keep it suitable for live analysis (mostly my roommate has been doing this), a Dremel "drill press" with a small endmill is used to make a cavity above the die. We use a rough estimate, usually slightly above the pins, to guess how far to go down. The package is pre-heated to 300F and a drop is put on top, allowed to etch, and washed with acetone before it dries out. Heating the acid doesn't seem to make a difference as its heat is negligible (plus transfer cool off) compared to many IC packages. I also played around briefly with another low cost method that is more automatic but less selective, I'll try to post something on that soon.
Finally, I'm interviewing with various companies and looking for a job, so if you think you might be interested in me, feel free to send me an e-mail at JohnDMcMaster gmail.com.