Tuesday, January 28, 2014

Not one direction, a new direction

I decided to change up bityExpress a bit given what I've learned on the last few board builds.   The upgrades include:
  • The entire design is now single-sided SMT.  This should be much easier to paste and assemble myself.  I'll only need to order one stencil, and I won't have to worry reflowing the board twice or deal with back-side components preventing the board from being level while I paste the top-side.  There may be a SI (signal integrity) price to be paid for moving the decoupling capacitors a little farther away from the FPGA's power pins, but this layout still exceeds Altera's guidelines. I'd also like to start testing my SI rules-of-thumb.
  • I've removed the JTAG programmer and switching power supplies that I've already validated.  They really only added cost and assembly time at this point.  I'll consider re-adding them if I ever decide to build the board in larger volumes.
  • The board is now much more rectangular than it was.  This should make it fit better inside OSH Stencil's jigs;  Pasting should be easier and faster.

3D model of bityExpress-C
I ordered the updated card from OSH Park today and was assigned to today's panel!

1 comment:

John Sloan said...

I forgot to mention that I bumped up all of my vias to 20 mils (5 mil annular rings rather than 4 mils). I also restored my BGA pad size to the (slightly larger) Altium defaults for Altera's F484 package.