It is reported to be an 8 layer PCB. Probably atleast a 2-3+ HDI.
PCB Layer 4/8 (Now from the back, flipped for ease of alignment.) Another solid ground plane.
PCB Layer 5/8 (flipped) Power planes.
PCB Layer 6/8 (flipped) Two sneaky DDR memory pairs routed on this layer.
PCB Layer 7/8 (flipped) ground plane - Note: 2 cutouts in this plane, that seem to correspond to SW signals of DCDC buck converters. I've never seen that before? Maybe to reduce capacitance on the SW pin?
PCB Layer 8/8 (flipped) bottom layer
Pinout Mapping (WIP):
a dump of the SPI communication (and the decoded flash data) can be found here: