Standardization for System-On-Module connection?

[Jacob Hrbek]

   I am working on an OSHW rugged tablet for which i want to make the PCB
   modular, hackable and economical for fabrication.
   To do that i was thinking that i can take an inspiration from OLIMEX's
   SOM-204 project which is a solution of 2 Printed Circuit Boards
   ("PCBs") where one PCB is the "Module Board" which has the chip, ram
   and anything that is specifically relevant to the chip and is usually
   4~12+ layers that slots in an "Evaluation Board" which has various
   connectors, devices, etc.. and is significantly larger in size and 1~4
   layers.
   The idea is that the "module board" can be fabricated in high
   quantities thus making the cost of fabrication for high layer PCBs not
   painful (can go as high as 1500+ EUR/USD in low quantities) that can
   then be slotted in a "platform board" which is a very economical to
   fabricate (usually around 25 EUR for 5 of them) so it can be adjusted
   to any formfactor and project and then combined with "module board"
   from a distributor for the cost of the components + fabrication
   (usually it's cost of the components + ~10 EUR)
   And because the "module board" can be basically used for anything this
   way then it's fabrication in high quantities makes sense economically.
   But the solution by OLIMEX is limited on 204 pins as it's using DDR3
   SODIMM connector with 204 pins where the obvious solution would be to
   use DDR5 SODIMM which has 262 pins, but i think that there are
   alternative solutions that would make that platform more functional
   which i want to brainstorm.
   So i've written down the issue and ideas
   in [1]https://git.dotya.ml/kreyren/OSHW-System-On-Module and i want to
   propose it as standard that people can integrate in their project (thus
   lowering the cost of "module board" where the cost goes down the more
   popular the module board is to buy) while enabling anyone to make any
   OSHW/Free and Open Source Hardware Designs and fabricate them locally
   for a cost that the generic consumer can afford painlessly.
   In practice the abstract of making said tablet is:

    1. Downloading the libre KiCAD designs for the "platform board" and
       sending them to local PCB fabricator (~25 EUR for 5 PCBs)
    2. Buying the "Module Board" - For reference i bought OLIMEX's A20-SOM
       ([2]https://www.olimex.com/Products/SOM/A20/A20-SOM) locally for 13
       EUR/USD including shipping, first hand costs 35 EUR/USD
    3. Download the chasis implemented in OpenSCAD/LibFive (projected to
       be generatable depending on what devices and configuration the user
       wants) and put that on a 3D printer (optionally using pre-optimized
       print to skip the slicer phase and get reproducible results (for
       technical materials as the chasis is designed to be printed using a
       PolyPropylen + GF30 which is very difficult to print)
    4. Source additional components such as touch screen display, etc.. -
       Projected to have a list of compatible monitors and mediawiki for
       people to add where these can be bought locally.. I can get a 10"
       touch screen display for <5 EUR from a e-recycling center which
       usually has a lot of them (and the chasis is functional design that
       can be generated to fit the display), ~30 EUR from second hand and
       30-80 EUR online e.g. OLIMEX sells one for 78
       EUR [3]https://www.olimex.com/Products/OLinuXino/LCD/LCD-OLinuXino-
       10/open-source-hardware
    5. Put it all together to get fully libre tablet for ~40 EUR + cost of
       the components and fillament + 3D print, assuming that people have
       access to 3D printer or makerspace where they can use one (I have
       access to the 3D printer for free sponsored by city of Brno to all
       citizens and local makerspace costs ~5 EUR to use for a day outside
       of membership or asking makerspace member to let you in and print
       it for them for the cost of fillament) that you can adjust to any
       kind of computing you want for ~25 EUR for new platform PCB.

   Brainstorm, merge requests and anything relevant to the project is very
   appreciated!

   -- Jacob "Kreyren" Hrbek

References

   1. 
https://git.dotya.ml/kreyren/OSHW-System-On-Module/src/branch/central/README.md
   2. https://www.olimex.com/Products/SOM/A20/A20-SOM/
   3. 
https://www.olimex.com/Products/OLinuXino/LCD/LCD-OLinuXino-10/open-source-hardware