Motor Control Setup
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Because changing to 4 layers only gives you more routing resources - it does not automatically fix bad copper geometry, broken net continuity, or unfinished routes.
For Flux’s PCB workflow, stackup change is just part of setup; you still have to get through placement/grouping/routing, and the route stage is what actually classifies nets and applies routing priorities. In other words, 4 layers helps, but it does not by itself complete routing or resolve all copper conflicts
Why you can still see airwires
Airwires mean there are still nets that do not have continuous copper between the required pads. A stackup change does not remove those - it just gives the router more layer options. Flux review treats airwires as unresolved routed connections, and they stay until the route is actually completed
In your board, the remaining airwires were already concentrated on a few power nets:
So the likely reason is simple: those rails are still not fully connected, even though the board now has inner layers.
Why you can still get overlapping copper
Overlapping copper usually means two copper objects on the same layer occupy the same physical space in a way Flux considers invalid. Going from 2 to 4 layers reduces congestion, but it does not automatically:
- move old traces out of the way
- remove stale copper from the previous route
- fix a floating copper island
- reassign a trace to a different layer
- clean up fills that now collide with traces or other fills
That lines up with your earlier state where the board still had a floating copper issue after the 4-layer conversion. A stackup change can leave old geometry behind that still needs cleanup.
The most likely causes on your board
In order of probability:
Table
| Cause | Why it happens after 4-layer conversion |
|---|---|
| Old 2-layer routing still exists | Existing traces/fills were not fully reworked for the new layer plan |
| Partial trace stubs remain | Same-net traces exist but don’t quite connect, so airwires stay |
| Copper fills need refill/recheck | Plane/fill geometry may now collide or isolate regions |
| Router did not reprioritize critical nets | The route stage still needs clear power-net intent and room to work |
| Some copper is on the wrong layer | 4 layers help only if the critical routes are actually redistributed onto those layers |
Short version:
-
Unroute or delete leftover problem traces/fills
- Especially any old 2-layer compromises on the power nets.
-
Refill / recompute copper
- If there is a floating copper or overlap warning, stale copper geometry is a prime suspect.
-
Route the board again in order
- First: main 12 V rails
- Then: 5 V / 3.3 V
- Then: motor outputs
- Last: logic signals
That order matches the recommended PCB workflow: setup first, then route with net-type and current priorities, not the other way around
- Use the inner layers intentionally
- L2 Ground Plane
- L3 Power Plane
- Don’t keep forcing everything onto top/bottom just because that’s how the 2-layer version was being solved.
Your 4-layer board is probably not failing because “4 layers didn’t work.” It’s more likely that:
- you still have unfinished rails creating airwires, and
- you still have legacy copper/fill geometry creating overlap warnings.
So the fix is usually:
- clean out the leftover copper that no longer makes sense,
- then reroute with the 4-layer stackup in mind.
Give cleanup checklist
Check current DRC
Focus on Net 53
Finished working
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