If you have not read about the “Stateless Laptop” proposal, please read it, it covers modern Intel firmware/hardware security issues:
http://blog.invisiblethings.org/2015/12/23/state_harmful.html
One part in the article talks about how to trust silicon:
The physical protections mentioned above do not, however, resolve the problem of the attackers subverting the laptop hardware at manufacturing or shipment stages. This includes, naturally, a potentially conspiring laptop vendor. In order to address this latter problem we — the industry — need to come up with reliable and simple methods for comparing PCBs with each other. A tool analogical to ‘diff’, only working for PCBs rather than on files. Such a tool, implemented as a software, could e.g. take two (sets of) photos taken by the user of the two boards to compare. The photos might be taken with an ordinary camera, or, in a more sophisticated setup, using X-ray imaging to reveal also the internal layer wiring. This inititive has already been proposed by other researchers recently (e.g. [@appelbaum_technical_action_plan]), so it is not unreasonable to expect some progress in this area in the near future.
So when Make Magazine retweated a recent PCB Xray project, I thought of the above:
Homemade X-Ray Inspector Reveals PCB Secrets
Anyone who has ever tried to reverse engineer a printed circuit board is familiar with the frustration of tracing out the connections by eye and by multimeter. It’s a long process, and if there are multiple layers to the board, you may not even get the full picture. It would be a lot easier if you could just see through the board. On an industrial scale, X-ray inspection machines are used for this, but as you might suspect, they’re not cheap. So, hardware hacker John McMaster built his own.
Firmware Security 