Thoughts about cost optimization and risks
Added 2016-04-22 05:33:10 +0000 UTCTalking with a friend about FPGA development boards made me realize how painful it would be to have the FPGA fail on the verification board, knowing it would be in BGA and next to a bunch of other components.
$400 isn't that steep of a price for such a project, but burning up 3/4th of it by accident would be a big disappointment for everyone.
To minimize the risks, I came to consider a two-board solution:
* A big 2-layers board with all the connectors, 68k work RAM, flash, level converters and DACs.
* A smaller 4-layers board with only the FPGA and its configuration memory.
Since only the FPGA requires a 4 layers board, it would be a waste to route everything else on the same big and expensive board. Furthermore, if the FPGA dies for some reason, only part of the system would need replacement (or a revision).
I was looking for some mezzanine connectors for that solution and couldn't really find reasonably priced and sized ones to route ~180 I/Os. 0.4mm pitch next to plastic is scary, and 3 pairs of $4 connectors isn't very cost efficient.
Then I came across SODIMM connectors: cheap, vertical versions available, 200 pins, and doesn't require another connector on the plugged board !
I need to re-evaluate costs, but I guess making a separate FPGA module and switching to 2 layers for the "motherboard" will easily save $50 and lots of stress during the smoke test :)
