Wednesday, February 24, 2016

Progress on the ALU board

With six copper layers to play with, routing the ALU board has gone from challenging (if not nightmarish) to relatively easy. When routing vertical traces I no longer have to consider how I'm going to get VDD to the various pads, and routing nets to the connectors is mostly a matter of keeping routing lanes free of vias to avoid having to weave around them.

Here's a snapshot:

The six-layer stackup is:

Layer Color Usage
1 Red Top: SMD pads, simple routing
2 Hatched Red Ground plane — not shown
3 Dotted Green Unused, probably inter-board nets
14 Light blue Mostly vertical routing
15 Hatched Blue VDD (power) plane — not shown
16 Blue Bottom: Mostly horizontal routing

All of the VDD and GND nets have been routed. Ratsnest shows only 58 airwires remaining, though that will rise when I finish assigning inter-board nets to connector pins.

At this rate I could have both the ALU and ID boards completely laid out in a week or three. That assumes that I decide to keep using FDV301 and BSS83 FETs as high-side push-pull drivers and not switch to DMN26 parts.

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