KB: Resolving 'Unknown Pin' Validation Error During PCB Import in Altium Designer
Created: November 11, 2025 | Updated: November 11, 2025
Altium Designer
When importing schematic changes into a PCB layout using Altium Designer’s Engineering Change Order (ECO) process, users may encounter a validation error labeled "Unknown Pin." This error occurs because the system attempts to validate net assignments before the associated footprints are physically placed. Although the error appears during validation, it does not affect the final result. Executing the ECO in two passes—first placing footprints, then assigning nets—ensures successful validation and correct net assignment.
Solution Details
Validation Error: 'Unknown Pin' During PCB Import
Why the 'Unknown Pin' Error Occurs
During the ECO validation phase, Altium Designer checks whether each proposed change can be executed. For footprint-related changes, it first validates whether the footprint can be placed. However, since the footprint is not yet physically placed, the system cannot assign nets to its pads. This causes the validation for net assignment to fail, resulting in the "Unknown Pin" error.
Impact of the Error
This error only affects the validation phase and does not indicate a critical issue. Once the ECO is executed and the footprints are placed, the system can correctly assign nets to the pads. Therefore, the error does not impact the final PCB connectivity or design integrity.
Recommended Workflow to Avoid the Error
To ensure a clean and error-free ECO process, perform the ECO in two passes:
- First pass: Place footprints without assigning nets
- Second pass: Assign nets after footprints are placed
Step-by-Step Instructions
- In the PCB document, go to Design » Import Changes from [Project Name].
- Click Validate Changes.
- Locate any net assignment items showing the "Unknown Pin" error.
- Right-click one of these items and select Disable all of the same kind to temporarily skip net assignments.
- Click Execute Changes to place the footprints.
- Repeat Design » Import Changes from [Project Name].
- Click Validate Changes again — the validation should now succeed.
- Click Execute Changes to complete the net assignments.
Additional Notes
- This issue typically occurs even when the schematic has zero compilation errors.
- It is safe to proceed with executing the ECO despite "Unknown Pin" validation errors, as long as the final result is correct.
- Running the ECO in two passes ensures proper validation and net assignment.