My board had a big blob of thermal paste spilling over the side of the chip which made it impossible to count the pins when trying to locate the reset pin, I tried angling the board in the microscope but ended up having to scrape it away.
I was super careful using the back of an exacto-knife and some tweezers and it it seems to have come away ok but the pins were still slightly obscured and I was off by one when counting.
Board still works (though I was sweating when I turned it back on…) but I was wondering if you had any general tips for this situation, i.e. how to clean a board properly without potentially damaging any lines etc?
Sloppy thermal paste is a pretty common problem - probably more common than anything that is intentionally used to prevent reverse engineering a board.
Typically, if I’m analyzing a target, i want 3 devices: One I expect to destroy, One I intend to use and analyze, and One I hope to keep as the pristine 'golden copy. In this case - i’d do the board level analysis on the ‘destroy’ board, which is the one i’d likely take apart completely and use to determine what the components are and where all the board traces go.
In the event you’ve got only one copy of a device - or even if you have three and are working on your ‘destroy’ board - there’s several options for removing most things. In general, it’s just a matter of finding the right solvent. In practice, I just start with the most mild ones and ramp up until it’s beyond my material safety tolerance. This usually means I try to gently ‘mechanically’ remove stuff first - peeling it off. After that I progress to isopropyl alcohol, and then possibly acetone. If none of that works, i let it dry completely and try heat. If all that fails, i go for rougher mechanical removal - whether that means chipping or sanding.