The first build of a new PCB design should be used to identify minor cosmetic and technical problems as well as to provide a board to test the design.  While any PCB shop will notify you of design problems serious enough to cause delay, it is less likely you will get a comprehensive list of less critical faults which may cause aggravation (or worse) in production or in the field.  DRC programs are great, as is a large amount of time examining the design details on the computer, but the best way to catch those last few glitches is if the designer assembles a board by hand or works closely with the assembly shop, making a hole size adjustment here or a reference designator move there, so the next fab spin will be clean.  Some shops will give you a virtual placement of the components on the design in PDF format so you can see how each part fits the land patterns, making it easy to identify clearance and land issues during design stage.  In this example the actual pads are shown in red, superimposed on the gerbers before the fab is started.  This is a valuable tool to quickly spot footprint errors, particularly if many new library parts are in the design.
2012 www.artcoengineering.com
Other Articles:
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PTC Fuses
About Reference Designators
Origin of Artco
About PCB Prototyping
Dryer PCB Failure
Avoiding Problems
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First Prototype Build