Designators

Overview

Designators are small component-identifying pieces of text that usually reside on both the circuit schematics and the top and bottom silkscreen layers of a PCB design.

A 0603 resistor and it's designator inside a CAD packages PCB design file.
A 0603 resistor and it’s designator inside a CAD packages PCB design file.

Resetting Designators

There are pros and cons to resetting the designators on a PCB:

PROS

  • You get to re-order┬áthe designators, this is especially true if there are now “gaps” (e.g. R8 and R10 exist, but there is no R9) after component changes have been made.

CONS

  • Component numbers may no longer match up between versions. This can be confusing when people refer to a component as “U7” on one version, but it is “U4” on the next.
  • Changing designator text lengths may cause silk-screen violations on PCB. For example, if the designator used to be “C96”, and is renamed to “C102”, it will now be longer and may, say, run into a copper pad on the PCB.
  • Component targeted rules and other design methodologies┬ámay stop working correctly if the CAD package uses the designators to identify the component. This is true with Alitum when defining classes and rules based of the designators.

 

  • Another problem can be that Altium (as of 14.1) does not update modified designators in rules. If you define a class or room with R1, R2, and R3, and those get changed to R11, R12, and R13, the rules will still have the original designators.

    • Thanks for the info, I have encountered the same issue before, and I have updated the cons list above.

      Regards, Geoff