A net class can survive a schematic update while its membership changes. The class name still appears in a rule, yet a renamed signal may no longer receive the intended clearance or routing requirement. Audit the member set after synchronization, especially when hierarchy or bus naming changes.
Altium’s class documentation describes classes generated from design structure and user definitions, with synchronization behavior controlled by project settings. Establish where each important class is defined so the schematic and PCB do not compete as undocumented sources of authority.
Record the expected set
For a critical class, list the intended nets and why they belong together. Use circuit function and pin endpoints to support the list. A name such as HIGH_SPEED is insufficient when reviewers cannot tell whether it includes clocks, data, strobes, or only a particular interface.
Distinguish classes used for browsing from classes used to apply design requirements. A navigation group may tolerate broad membership, while a clearance or topology rule can have material consequences if unrelated nets are included.
Compare before and after synchronization
| Set difference | Review question |
|---|---|
| Removed member | Was the net deleted, renamed, or unintentionally excluded? |
| Added member | Does the new signal require the same constraint? |
| Empty class | Does a rule now target no intended objects? |
| Overlapping membership | Which applicable requirement takes precedence? |
Review the proposed update before applying it, then inspect the resulting PCB classes. The proposal and final state are both useful: the former explains the intended change, while the latter confirms what the board actually contains.
Verify an affected requirement
- Select a representative retained member.
- Select a renamed or newly added member.
- Select a nearby net that should remain outside the class.
- Inspect the effective requirement for each.
- Run the relevant design-rule checks.
Checking only the number of members can miss replacement errors. An unintended addition and an unintended removal leave the count unchanged. Compare identities and inspect the circuit context of differences. Preserve aliases or rename mappings where they are needed to explain the change.
If the tool regenerates a manually maintained class, resolve the ownership and settings rather than repeatedly repairing the PCB by hand. Document any intentionally PCB-only class so later engineers understand why it is not reproduced by schematic data.
Close the review with the corrected class definition and the resulting constraint evidence. The differential-pair audit applies the same principle to pair objects, whose two-member relationships need verification in addition to broader class membership.
Move from reading to a build-ready project
Use the fabrication and assembly checklists to prepare drawings, production files and test requirements.
Open the DFM checklist