Protecting an Inductive PCB Sensor from Unintended Nearby Copper

An inductive sensing coil printed on a PCB interacts with conductive structures around it. A ground pour added during layout cleanup or copper thieving introduced for fabrication can change the sensor even though the netlist remains correct. Protect the intended electromagnetic environment in the manufacturing data as well as in the schematic.

Review the actual sensor family

Texas Instruments’ LDC sensor design guidance discusses minimizing nearby conductors around sensing coils, including ground and power planes. It also identifies device-specific differences in component placement. Use the selected converter and sensing topology to establish the appropriate layout requirements rather than applying one coil rule to every inductive design.

Mark the coil geometry, relevant capacitor, connection traces, intended target, and sensing distance. Inspect every copper layer beneath and around the coil. A keepout drawn only on the visible outer layer may leave an internal plane directly inside the sensitive region.

Carry restrictions into fabrication review

• Define the protected region and the layers to which it applies.
• State whether copper balancing or thieving is prohibited in that region.
• Review vias, test pads, mounting holes, and nearby connectors.
• Include shields, screws, brackets, and metal on adjacent assemblies.
• Compare the final manufacturing outputs with the approved sensor layout.

For example, an automatically filled ground plane on a new stackup can alter the coil environment without producing a conventional connectivity error. An electrical DRC pass does not demonstrate that the sensing structure was preserved.

Measure the final structure

Characterize the sensor with the intended target and mechanical assembly. Record converter settings, target position, environmental conditions, and any relevant raw measurements. Compare against the design model while keeping the model’s assumptions visible.

Evaluate tolerance extremes that affect coil-to-target distance and alignment. If a nearby metal part changes between product variants, measure those variants rather than assuming a common calibration is sufficient. The target is intentionally influential; unintended metal can be influential too.

The released package should include the sensor keepout, the permitted fabrication additions, and the configuration used for validation. Ask the fabricator to flag proposed copper changes in that region before production. When the stackup, enclosure, or coil geometry changes, reassess the response instead of carrying forward old calibration constants by default. This makes the sensor’s behavior a controlled result of the physical design rather than an accidental consequence of whichever copper and metal happen to surround it.

Archive the approved copper images with the characterization results so later comparisons can identify physical changes quickly.