I see two problems with mounting the SoC on the bottom, it needs a special case/cooling solution and you need to have a more expensive process if you want to mount 'heavy' components on both sides of the board during manufacturing (wrt reflow soldering, but also inspection steps).
I use a Fischer 14x14x14mm heatsink for PGAs on my Rock64 at the moment, and during kernel compilation on all cores which takes about half an hour, the temperature ususally does not rise above 70-72C which is still a good margin before throttling starts.
http://www.fischerelektronik.de/web_fisc...ndex.xhtml
They also have more low profile solutions with 6mm and 10mm heigth:
http://www.fischerelektronik.de/web_fisc...14x14x10_/$productCard/parameters/index.xhtml
I use a Fischer 14x14x14mm heatsink for PGAs on my Rock64 at the moment, and during kernel compilation on all cores which takes about half an hour, the temperature ususally does not rise above 70-72C which is still a good margin before throttling starts.
http://www.fischerelektronik.de/web_fisc...ndex.xhtml
They also have more low profile solutions with 6mm and 10mm heigth:
http://www.fischerelektronik.de/web_fisc...14x14x10_/$productCard/parameters/index.xhtml
Come have a chat in the Pine IRC channel >>