If you consider designing a custom NIO (carrier board)for Bedrock SOM, starting from Bedrock Cartridge is the way to go.

Bedrock Cartridge provides the following:

• Highly effective 1st stage thermal coupling (TIM0) to the Ryzen die to a copper heatplate.
  Coupling the heatplate to a heatsink/cold-plate is easy. Coupling the die is challenging.

• Provision for mounting NIO securely with accurate spacing.

• Easy mounting of SOM to enclosure / heatsink / cold-plate.

• Thermal coupling for SOM’s DC-to-DC converters

• Mounting of NVME SSD
  Not present on SOM itself

• Securing and thermal coupling for SODIMMs

• RTC battery compartment

• Physical protection and rigidity to the SOM

• Rigid chassis for the Bedrock Deck with multiple threaded mounting holes

Bedrock SOM

If you decide to design directly with Bedrock SOM, it is advised to use Bedrock Cartridge as reference.