PCB stackup for legacy Mojo V3 board

Help Request
1

I adopted the Mojo V3 back in 2016 as a base for a factory test jig which is still in use today. Now that Xilinx sorted out the situation with Samsung Foundry for fab space, Spartan-6 FPGAs are available once again after a big shortage. I thought it couldn’t hurt to make a few extra boards as a backup, so I took a look at the Mojo V3 Eagle files available here.

The PCB layer stackup shown in these files is very strange:

MojoV3_stackup
MojoV3_stackup965×619 23.6 KB

First, I’ve never seen a stackup that’s this asymmetrical. A clue that makes me think something is wrong is that the overall thickness adds up to 1.99mm, but my caliper measurement on a physical Mojo V3 board reports 1.56mm. Do you know what’s going on here and what is the correct stackup for this PCB?

2

That was just the default stackup in Eagle way back when.

The Mojo doesn’t have any special requirements. It was just generic 4-layer 1oz outer 0.5oz inner copper.

The Au and Pt are different and have impedance controlled traces for the DDR.

1 Like
3

Ah, OK. So the Mojo was never fabricated with this stackup. It’s just what was in Eagle by default. Gotcha. Thank you so much.