Autorouting in PCB Design
PCB design begins with a schematic.
The schematic can be a simple paper drawing on simple boards or captured in a CAD program for more complex boards, such as Altium or OrCAD. The connections on the PCB should be identical to the schematic, but while the schematic is readable, the PCB design is arranged to be functional. As a result, there is rarely any visible correlation between the schematic and the layout.
PCB design can be performed manually (using a CAD tool such as Altium Designer, PADs, or Allegro) or in combination with an Autorouter. The best results are always achieved using manual routing because the design engineer can exercise better judgment in arranging circuitry than an autorouter program. Many autorouted boards are often utterly illogical in their track routing because the program has optimized the connections but sacrificed any small amount of order that may have been put in place by manual routing.
Although autorouters have become much stronger tools, there is still no comparison between an autorouted board, and a hand routed board. Generally, autorouted boards are slightly more challenging for a technician to repair or debug for this reason. Furthermore, manufacturing yield is often decreased with autorouted boards. 911EDA does not autoroute any board unless we receive specific instructions from our customer.
The PCB design project consists of several layers (911EDA has designed boards up to 24 layers) for illustration purposes. The holes, outline, and component identification layers can be combined into one diagram. A PCB will usually have mounting holes and may have cutouts. By cutting an actual size check plot and placing it in the enclosure, you can see how it will be positioned in relation to other parts. We can also put components against the pad markings as a quick double-check of sizing.
911EDA puts a lot of effort into PCB design. It is somewhere where the quality of design can make a difference. These days, most circuit boards are automatically assembled and tested. But even with the automated process, there are still people working on most boards. A quality design can make all the difference between a product that is easy to work on and one that fights the process.
The silkscreen contains essential information that assists people in servicing and installing the product. A complete silkscreen identification overlay is used on most boards, and the quality of this is another way to make a better product. Aside from functionality, the overlay is the primary distinguishing feature between a purpose-built and general-purpose product. On a purpose-built product, terminals might be labeled as "+12v red" "-pwr black," "solenoid+" "solenoid-" whereas a general-purpose product might be labeled as: "A1 A2 A3 A4".
For dense surface mount boards, it is often necessary to leave off component values, and sometimes it is even required to omit the component designators. The silkscreen is the primary method for labeling connectors, replaceable parts, orientation, and even installation notes (for instance, "Remove J3 while replacing the battery - observe battery polarity").
Read our article Should I use the Autorouter in Altium PCB Design?
