PCB for my USB peripherals. (Proteus Ares) 2005

Designing your circuit can only get you so far.  Sooner or later you have to build something.  Years past it was possible to prototype simple circuits on veroboard or breadboards.  These days, many of the designs I use call for surface mount components even at the prototype stage.  The complexity and the clock speeds are such that it is necessary to build PCBs.  Usually if the design has been produced using schematic capture, a netlist can be exported.  The netlist effectively contains a 'roadmap' of all the junctions.  This can then be ported to the PCB CAD package.  This ensures that everything that needs to be connected is connected.  This then produces a rats-nest, where all the components are placed on the board with green lines showing what is connected to what.  Then each green line needs to be routed to enable the copper line to connect the parts.  For simple boards, this can be done automatically using an autorouter - but it will usually screw it up.  Its quite an addictive game to route boards by hand.  Everything conforms to a grid, blue is bottom, red is on top.  You can switch sides, but tracks on the same side cannot cross, or be too close.

Even if you have produced a board that conforms to these design rules there are other problems to consider for high speed or production designs.  Its imperative that track lengths are checked to ensure correct signal propagation, even at the speed of light we can run it to difficulties in pulses arriving late if they been a long way!  Also its important to be careful of the board layout to ensure EMC (ElectroMagnetic Compatibility).  This means making sure that your design does not emit string interference to other systems and is not subject itself to going nuts in the presence of external interference.

The Same PCB After Production (PCB Train)

When happy with the design, it can be produced using a wet etch system by corroding away the copper leaving just the tracks.  We can do this in the department, but again, for complex designs with lots of vias (tracks that swap sides) or 4 layer boards, its easier to have them produced outside.  All I need do is send them a gerber cad export file from the PCB package.  Five days later the PCB arrives on my desk.  Then its a case of soldering all the components including surface mount by hand, and hoping that its correct.  Minor screw ups can be fixed by cutting the tracks and re routing them using very fine enamelled wire, other screw ups can be bodged with firmware fixes!