The Hitchhiker's Guide to PCB Design

The Hitchhiker's Guide to PCB Design

Issue link:

Contents of this Issue


Page 80 of 115

81 PCB Documentation Finishing the routing, drilling, and design-checking completes only the graphic portion of a design, but there are other aspects of the design which the CAD data cannot address alone. For instance, CAD data defines the shape of an exposed component land, but not the metalized finish. CAD data defines the geometry for solder resist clearance and the graphic strokes for the assembly legend, but cannot define their color or composition. This graphic CAD data is not able to address the material requirements of the PCB, like temperature rating and structure. Graphic CAD data defines mostly geometric, nominal values for the features which are shown and this is critical for a designer to under- stand. There are no perfect manufacturing operations—every bit of CAD data will be subject to manufacturing tolerances. How will the effect of manufacturing variance and so many other aspects of the design be addressed? Data and machinery run the PCB process while graphic PCBA documentation is required to start the process. Graphic media is a tangible source for quotation and setup reference. The ability to view the finished PCB using a manufacturing print helps to start the fabrication process with the end in sight. Graphic PCB documentation also helps to close out and finalize the PCB process by giving the inspection stakeholders a graphic example of what the finished PCB will look like and provides notes and specification for its final electro-mechanical configuration. "Keep in mind the fabrication and assembly drawings each serve two purposes. They help the fabricator and assembler —serving as a guide, showing material basics—but they also serve as an inspection document for the quality assurance personnel." The Fabrication Drawing There are up to thirteen basic documentation elements which will need to be included in the fabrication drawing: Pro-Tip from Mike Brown

Articles in this issue

view archives of The Hitchhiker's Guide to PCB Design - The Hitchhiker's Guide to PCB Design