Notes about assembly
The repository https://gitlab.com/iccfpga/iccfpga-som contains everything needed for the FPGA-module.
Some notes about:
- My prototype boards were manufactured by JLCPCB. They are cheap and have incredible capabilities for the price.
- If another manufacturer is used, they have to be capable of 6 layer, 1mm PCB thickness, 3.5mil tracks, 0.2mm drills, ENIG coating. It's highly recommended to let do 45° bevelling of the card connector because the card-socket could be damaged.
- Impedance is important! If you order a PCB at JLCPCB use JLC2313 prepreq.
- it's very hard to assemble manually. It uses BGA and QFN packages and resistors and capacitors downto to 0402 size.
- if it's assembled manually, the only way is to use hot air with solder-paste and solder-stencil.
- there is another solder-stencil in the repository which doesn't include BGA pads. It's only for manual assembly. With solder-paste it's almost impossible to set the BGA by hand on the PCB without smearing the solder-paste which would probably give shorts. If you do it manually, only apply a thin layer of sticky flux on the PCB before putting the BGA on top.
- it's recommended to first assemble everything without the BGA and check voltages of step-down-converters. After they are confirmed good, then assemble the BGA. The BGA is a 45$ part and it would be very painful to destroy it because a resistor of a feedback voltage divider was assembled wrong.