Post 3 — From Copper to Netlist: Connectivity Extraction and Schematic Reconstruction (Done Like an Engineer)
At the heart of PCB reverse engineering is connectivity: which pins connect, through what structures, and with what intent.
1) Start with functional partitioning
Before chasing nets:
Identify sub-systems:
power input + protection
DC/DC stages and rails
MCU/FPGA domain
sensors/actuators
comms interfaces (USB, CAN, Ethernet, RS-485, RF)
Mark them on an annotated photo.
This “block map” gives you context: the same topology patterns repeat across products.
2) Build a rail map early
A rail map is a table:
Rail name (e.g., +5V, +3V3, VCORE)
Source component (converter/regulator)
Loads (ICs, connectors)
Sense/feedback network components
Power-tree clarity prevents schematic chaos later.
3) Connectivity capture methods (choose based on complexity)
A. Visual tracing (single/double-layer, sparse boards)
Strong when traces are visible and simple
Use continuity checks to confirm ambiguous jumps
B. Image-based layer alignment (more systematic)
Create aligned top/bottom copper images
Mark vias and through-hole pins
Build a net table from repeated patterns
C. X-ray-assisted inference (multilayer)
Helps infer planes (GND, VCC) and via fanouts
4) Net naming conventions (save your future self)
Adopt consistent net labels:
GND, VIN, VBAT, +5V0, +3V3
interface: USB_D+, CAN_H, CAN_L, SCL, SDA
control: EN_BUCK1, PGOOD_3V3, RESET_N
clocks: XTAL_IN, XTAL_OUT
5) Schematic reconstruction: top-down beats bottom-up
Instead of drawing every passive first:
Place major ICs and connectors
Add power blocks (regulators, inductors, diodes)
Add interfaces (termination networks, ESD)
Add passives around each IC (decoupling, pull-ups, RC filters)
Validate against common reference designs and expected pin functions
6) Validation checks (catch errors before layout)
Every IC power pin has decoupling and correct rail
Ground pins are truly ground
Differential pairs have plausible routing and termination
Feedback networks match regulator topology
Protection devices are oriented correctly
No impossible shorts (rail-to-rail without reason)
