Inspection focused on the ESC motor outputs A_PAD, B_PAD, C_PAD, MOSFETs Q1–Q6, copper/via usage, and thermal bottlenecks.
Layout Context
Table
Item
Observed value
Board size
26 mm × 13 mm
Stackup
4-layer PCB
Copper thickness
0.035 mm / 1 oz on each copper layer
Power MOSFET layer
Bottom
Motor output pad layer
Bottom
Motor output pad size
2.5 mm × 2.5 mm each
MOSFET footprint
TPN22006NHLQ-FS
Default visible trace width
0.1524 mm / 6 mil
Thermal relief setting on inspected pads
Direct connect
Component density
Critical, about 73.1% component-area fill
Phase Mapping
Table
Output
Switch-node net / phase
MOSFETs
Driver
A_PAD
Phase A
Q1, Q2
U2 / MP1907AGQ-P
B_PAD
Phase B
Q3, Q4
U4 / MP1907AGQ-P
C_PAD
Phase C
Q5, Q6
U5 / MP1907AGQ-P
Findings
1. Visible routed traces are far too narrow for 40 A
The extracted layout geometry shows many route segments around the inspected regions at 0.1524 mm width. That is appropriate for signal routing, not for the 40 A phase, VBAT, or ground current path.
This means the high-current capability must come from copper pours / polygons, large pads, and distributed plane copper — not the visible 6 mil traces.
2. Output pads are large but need uninterrupted copper spreading
A_PAD, B_PAD, and C_PAD are each 2.5 mm × 2.5 mm bottom pads, which is a reasonable connector/solder land size for a compact ESC. The risk is not the pad alone; the risk is necking between:
MOSFET source/drain pads and the phase pad
MOSFET drain pads and VBAT copper
Low-side MOSFET source pads and GND copper
Any layer transitions used to spread current/heat
3. MOSFETs are compact and all on the bottom layer
All six TPN2R703NL MOSFETs are on the bottom layer. This is compact and good for short phase loops, but it concentrates heat in a small area. The full MOSFET group occupies roughly 13.29 mm × 11.44 mm, nearly the full board height.
4. Current sharing through vias was not positively verified
The automated review did not report current-density or via-capacity errors, but the layout extraction did not expose a clear via array dedicated to each phase, VBAT, and GND path. For a 40 A ESC, this is a risk unless the copper is intentionally spread across multiple layers through many vias.
5. Protected-polygon intrusion warnings are relevant to high-current copper
Current DRC reports 12 protected-polygon intrusion warnings. Because this design depends heavily on copper polygons for high-current carrying capacity, these warnings should be treated as important, not cosmetic.
Potential effects:
Unintended copper keepout/polygon clipping
Reduced effective copper width
Narrow thermal/current bottlenecks
Unexpected current crowding around intruding vias or pads
6. 1 oz copper is aggressive for 40 A on this board size
The stackup uses 0.035 mm copper on each copper layer. A 26 mm × 13 mm ESC can work at high current only if the layout uses broad, parallel copper areas, short loops, heavy via stitching, and strong heat sinking to motor/battery wires and airflow.
Likely Bottlenecks
Table
Area
Risk
MOSFET pad-to-phase-pad copper
Current crowding and resistive heating if narrowed by routing/polygon gaps
Low-side MOSFET source-to-GND return
Ground bounce, heat, and switching noise if return path is not a broad copper plane
High-side MOSFET drain-to-VBAT
Input ripple current and localized heating if VBAT pour is fragmented
Layer transitions
Via heating if current is forced through too few vias
Protected polygons
DRC warnings may indicate copper intrusions or reduced clearances in critical pours
Board density
Limited copper area for heat spreading and limited room for via arrays
Recommendations
Verify high-current polygons visually and electrically
Confirm A/B/C, VBAT, and GND are large copper pours, not only narrow traces.
Resolve the 12 protected-polygon intrusion warnings before relying on the pours.
Add or verify via arrays
Use multiple vias near each MOSFET drain/source copper island and near each motor pad.
Prefer dense stitching between bottom copper and internal/top copper for VBAT, GND, and phase copper.
Avoid neckdowns in phase/VBAT/GND copper
Keep the narrowest high-current sections as wide and short as possible.
Do not route signal traces or via keepouts through the center of phase-current copper.
Use direct-connect thermal settings for high-current pads
The inspected pads already show direct connect, which is correct for current and thermal performance.
Avoid thermal relief spokes on MOSFET power pads and output pads.
Consider heavier copper for production
2 oz outer copper, or thicker copper on all layers, would improve margin.
If staying at 1 oz, rely on airflow, short duty peaks, and wide copper sharing across layers.
Run a targeted current-density/thermal analysis if available
The present automated checks did not produce PI warnings, but that does not prove the path is thermally safe.
Use measured or simulated RMS phase current, expected airflow, copper thickness, and duty cycle.
Bottom Line
The layout is very compact and likely depends on copper pours for current capacity. The visible 0.1524 mm traces are not adequate for 40 A by themselves. The most important next step is to verify and clean up the high-current polygons, especially because protected-polygon intrusion warnings are present in the current DRC results.
Layout Context
Phase Mapping
Findings
1. Visible routed traces are far too narrow for 40 A
2. Output pads are large but need uninterrupted copper spreading
3. MOSFETs are compact and all on the bottom layer
4. Current sharing through vias was not positively verified
5. Protected-polygon intrusion warnings are relevant to high-current copper
6. 1 oz copper is aggressive for 40 A on this board size