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The layout of a printed circuit board can be done manually using CAD, or alongside an auto-router. You will find that the best results are achieved by using at least some manual routing because the design engineer is better able to judge how the circuitry should be arranged. Often times, boards that have been auto-routed end up with completely illogical track routing. While the program can optimize the connections, it also sacrifices any amount of order that an engineer can put in place through manual routing. Auto-routed boards are also harder for an engineer to repair or debug. There are several layers within a CAD printed circuit board. When using illustration, the layers will be colored and compressed into one overlay image. However, when you are actually laying out the boards, it is best to use actual size check plots during the design process. Overlays usually have to be enlarged and printed out to show all the detail, but an actual size print with mounting holes and cutouts is a great check tool. Prints are helpful because you can place them inside the actual enclosure and see how it will be positioned in relation to all the other parts. Components can also be placed up against the pad markings, allowing you to check the dimensions. There are a few variables that determine how wide your tracks can be, such as current flow, space available, size of parts, and electromagnetic interference. When designing the track layout, pinpoint where the current needs to dodge from one side of the board to the other to avoid any obstacles. You should try to find the shortest regular path between the connected points. While designing the loop area, consider impedance, susceptibility and signal on the tracks. These days printed circuit boards are automatically assembled and tested, but there are some people who still like to install and repair them by hand. Whether you love or hate working on a printed circuit board will depend heavily on the quality of its design. Machine test points only need to be plain pads or lands. There are some test points that are intended for engineering test or modification, which can be labeled with circled pads. If you really want to create a great printed circuit board, add a complete silkscreen identification overlay that contains important information that will assist people in serving and installing the product. Aside from functionality, the chief distinguishing feature between a purpose-built product and a general-purpose controller is the silkscreen overlay. The silkscreen is the best method for labeling connectors, replaceable parts, orientation, and even installation notes. You could also use it as a backup for manufacturing notes, even though those are normally included in the BOM.
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