I’ve been working with the BeagleBone Black and discovered today that I had a bad SD card. Not only could I not access it, but it was also getting hot. Instead of just throwing it away, I decided to do what any other curious person would do – I removed the solder mask so I could get a look at the layout.
These devices are basically just PCBs with flash memory molded into the substrate. I do a lot of PCB layouts, but this was particularly impressive to me, given the trace/space distance and the free form trace routing. Due to the transfer speeds and layout requirements some of the traces are probably length-matched, which would help explain the routing. Also, this is done in a very restrictive form factor.
I got some images with my digital microscope, so you can really see the detail.