[gta02-core] FYI: PCB/SMT parameters

[Werner Almesberger]

For checking PCB making and SMT compatibility, I compiled this list of
board parameters:

- PCB size is about 10 x 6 cm2.
- PCB has 8 layers, 1 mm overall thickness.
- Minimum trace width is 4 mil, with a 4 mil clearance between traces
  and between traces and pads.
- Surface finish is probably ENIG (need to confirm)
- Not sure about the laminate.
- PCB has components on both sides, about 10% on one, 90% on the other.
- Total number of components on the PCB will be about 350-450.
- Approximately 120-160 of the components on the PCB are unique.
- There are about 20 components that don't have a standard chip
  package (connectors, buttons, shields, etc.)
- Largest component is currently a 27 x 18 mm2 SIM/SD combi-cardholder,
  but we may add an LGA module of about 30 x 25 x 3 mm3.
- Largest chip is a 14 x 14 mm2, 0.5 mm pitch 332-FBGA (SC32442)
- Smallest component is 0402.

I left a bit of wiggle room for the modem and such.

- Werner