Reference Designator Best Practices
Dropping the reference designators on your quick-and-dirty design might seem like a good place to save time, but most veteran designers can tell you multiple horror stories trying to figure out a board design later. Matching reference designators on the schematic to the board layout can be valuable. Moreover, telling the person doing the assembly where to put each component absolutely depends upon the reference designator.
There are a number of ways in which a designer can organize the reference designators.
A Simple Design Order
Number ranges to indicate which sheet of the schematic sheet 1 = 1xx, sheet 2 = 2xx, etc. This approach is particularly useful if you expect field-replacement of individual components will be your most likely ongoing task.
Number ranges indicate which side of the board the component was placed R100-R499 = top side, R500-R999 equal bottom side. This method is valuable when a component search will start with the schematic and end with locating the part on the board.
And, of course, there are many ways to mix the two:
Txyzzz = Top, X=component type, y = schematic sheet, zzz = component number
Bxyzzz = Bottom, X=component type, y = schematic sheet, zzz = component number
Production and field support folks will tell you this:
“I have worked in production, and I can wholeheartedly say that a properly annotated board makes a real difference. I always prefer a PCB-oriented systematic annotation to a schematic one. In the absolute majority of situations you need to find a specific component on the PCB based on the schematic, not the other way around.”
One thing to plan for is how sophisticated your CAD tool is about letting you renumber the components to follow your encoded logic once your design is complete.
Regardless of your naming conventions for reference designators, PCB123 will keep the schematic, layout *and* the BOM accurate and up-to-date, allowing you to more easily consult with the assembly team, and field services.