Hello !
I'm developing my first commercial electronics product and I have reason to some believe some people will want to steal the contents of RAM (there is a history of IP theft in that domain). On top of that, I use the RP2040, which doesn't have an internal flash (and thus any form of security measure). Finally, patents are way too expensive for one random guy like me.
Given that, I'm still trying to make it very hard to reverse engineer the device. Aside from any software things like encrypting the firmware in place or making it hell to read the ASM, I was planning to use a potting compound to prevent access to the electrical components.
At first I tried some random epoxy off Amazon (meant to make fantasy jewelry & other mold-based things - Dr Crafty). That didn't work very well. I could scrape off the cured epoxy with a knife, and I could cut it too, and once there was enough of a dent, I could remove it by hand and it would separate from the PCB. So clearly, far from enough adherence to the PCB.
Fine then, maybe I should use something
meant for potting compounds as my potting compound. So I got some MG Chemicals 8810 Black Rigid Urethane. Unfortunately that's not working out very well for me either.
Two observations here: I put what I would consider a "normal" amount of coating on the right PCB, and it would seem bubbles have formed as in, the volume at least tripled. ... In fact the PCB does not fit in its enclosure anymore.
In my subsequent tries, I put few droplets, and I get something that, while having significantly grown in volume, at least doesn't render the PCB unusable. That's a very annoying behavior I didn't expect, and I'm not sure is expected. Also, I would guess that these bubbles lower the resistance, I mean, I can pierce them with a knife...
Secondly, I find this not that hard to remove. It's not as easy as the epoxy I used previously, but I would expect someone determined to be able to remove enough of it to access the interesting parts without any need of resorting to hazardous chemicals, in other words, it doesn't do the job.
We're very far from what I can read about the efficiency of these compounds in places like
https://www.eevblog.com/forum/repair/removing-black-little-rubbery-feel-potting-compound/ where people agree it's very difficult to remove, for instance I read
"To make a long story short: Theres no "chemical" way to remove it without damaging the parts or PCB that i know of.
If it's the soft stuff, you just remove it with a cutter piece by piece, hoping it does not stick to well to the plastic foils around caps etc.
The problem is, once you cleared the PCB, i may be impossible to tear the PCB from the resin underneath without breaking it.
If it's the hard resin: Forget about it. I'm not saying it can't be done, but it's a fools errand. "So, what am I doing wrong here ? It should be noted that since I was mixing droplets (10 droplets of A, 5 droplets of B...) the 2:1 ratio may not be perfect.. but still. What is this "hard resin" ? Am I using the wrong chemical ? Or just doing things wrong ? On that note, if I could use a chemical that doesn't behave like yeast, that'd really make my life simpler.
Thanks !
Regards, JB