Review NC, DNC, and Reserved Pins Before Creating a Symbol

A pin marked NC, DNC, reserved, or test should not be assigned a connection policy from its abbreviation alone. Device documentation may distinguish a pin with no internal connection from one that must remain unconnected or be held in a specified state. Capture that distinction when creating or reviewing the symbol. Record package-specific exceptions beside the affected pin rather than burying them in a general library note.

In its TLC2201-SP support response, Texas Instruments distinguishes NC from DNC. This is useful context, but the exact device and package documentation remains the authority for your design. Do not turn a response about one part into permission to reuse every NC pad as a routing point.

Build a pin disposition table

Include exposed pads and pins whose function changes with package or operating mode. If the documentation is ambiguous, raise a specific question identifying the full part number and the proposed connection. Keep the answer with the library record.

Make the CAD model reflect the requirement

A no-connect marker communicates deliberate nonconnection to the schematic checker. It does not establish that the manufacturer’s requirements permit nonconnection. Likewise, hiding a pin for a cleaner drawing does not remove the physical pad or make arbitrary board copper acceptable.

Review the footprint separately. Check that restricted pads are not inadvertently connected by a copper fill, pad-number reuse, or inherited thermal-pad assignment. Where a physical pad is retained without a net, inspect the fabrication copper around it rather than assuming the schematic marker controls every geometric detail.

Recheck during substitutions

1. Compare the proposed part’s full pin table with the approved one.
2. Identify every changed NC, reserved, test, or supply requirement.
3. Review symbol and footprint treatment for those pins.
4. Inspect the placed board and any connected copper.
5. Regenerate checks and manufacturing outputs after approval.

A mechanically compatible replacement can assign a function to a formerly unused contact. That makes the board treatment of the old pin part of the substitution decision, not an incidental library detail.

Complete the review when every physical contact has an explained disposition. Keep unresolved pin requirements visible; suppressing a warning is not a substitute for resolving the component documentation. Use the pin-map audit to verify the rest of the package at the same time.