Design Rule Checking (DRC) is also a very important activity at the end of a PCB design. It allows you to automatically check your PCB design for connectivity, clearance, and other manufacturing errors. With the large and complex PCBs being designed today, it is impractical to manually check a PCB design. This is where the DRC comes into its own, it is an absolutely essential step in professional PCB design.

Some examples of what the designer can check with DRC in various CAD systems are the following:

Ø Circuit connectivity. It checks that every track on your board matches the connectivity of your schematic.

Ø Electrical clearance. You can check the clearance between tracks, pads, and components.

Ø Manufacturing tolerances like min/max hole sizes, track widths, via widths, annulus sizes, and short circuits.

A complete DRC is usually performed after you have finished your PCB. Some packages however have the ability to do "real time" (or "online") DRC checking as you create your board. For instance, it wont let you connect a track to a pad it shouldn’t go to, or violate a clearance between track and pad. If you have real-time DRC capability, use it, it’s an invaluable tool.

Sometimes it is necessary to perform annotations, which are forward and backward. Forward Annotation is when you make changes to your existing PCB layout via the schematic editor. The program will take your schematic netlist and component designators, and import them into your PCB design, and making any relevant changes. Some packages will also automatically remove old PCB tracks that are no longer connected. You can do this at any time during your PCB layout. If you update your schematic, then you must forward annotate into your PCB design. You can do edits like this manually, but forward annotation automates the process.

Back Annotation is when you change one of the component designators (eg. "C1" to "C2") on your PCB and then automatically update this information back into your Schematic. More advanced back annotation features allow you to swap gates on chips, and perform other electrical changes. There should never be much real need to use back annotation.