The Hitchhiker's Guide to PCB Design

The Hitchhiker's Guide to PCB Design

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Page 79 of 115

80 Gerber Data Files for All Required PCB Artwork Layers This is the starting point for graphic CAM tooling. Referred to as "artwork" the supplier modifies this data to conform to their manu- facturing capabilities to meet finished feature requirements specified in the fabrication drawing. After the layout is complete, the software can output these files, each of which will become the basis for the etched copper pattern for each PCB layer. When outputting Gerber file data, use the very common RS-274X output. This selection utilizes special technology referred to as "embedded apertures" to create the artwork shapes. Industry Standard Design Continuity Verification Output IPC-2581 or ODB++ design output and an IPC-D-356 format netlist will help the PCB supplier check to make certain the artwork matches the design intent electrically before and after fabrication. The more intelligent and comprehensive the data, the better. Industry Standard Drill File A common output format is Excellon. Drill files define the nominal X, Y position of the holes, but keep in mind, the numeric values output from CAD software define the finished hole size, not the drill size. Drills must be larger than plated holes specified to compensate for plating thickness; the supplier will select the appropriate drill size. Neutral Database File Providing the source file for the complete design database allows a PCB supplier to access the source data needed to determine design intent. Unlike "dumb" graphic Gerber data, source data provides intelligent data, net names, and connectivity information which can be helpful in determining artwork anomalies and moving the design through the CAM process quickly. Intelligent source database formats are best output in IPC-2581 or ODB++, but some systems accept ASCII output of the original layout database.

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