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30 DESIGN007 MAGAZINE I JUNE 2023 Is CAD data output enough to move your design through to global manufacturing suc- cess? Form, fit, and function are oen referred to in the context of part interchangeability. How well will parts fit together with other parts aer rolling off a manufacturing produc- tion line? Without key specification limits for these physical performance requirements, a PCB design is destined for quotation delays, no-bids, or outright manufacturing rejection. ese can kill time-to-market product devel- opment goals. CAD Data is Absolute If you have ever opened a CAM file gener- ated from your CAD layout tool, you have seen hundreds of numeric values, each representing a geometric data point in the design. Some of these values specify where the center of a trace is to be located aer printing, plating, and etching. Some values represent a location for the center of a hole to be drilled or a milling path for a slot or board edge. Some of the data tells a machine how fast to spin and where to rotate or move to perform the work. All CAD layout tools output absolute data, and those points nominally represent the exact, theoreti- cal position—the target condition—of a geo- metric feature. CAD Data Doesn't Account for Manufacturing Process Tolerance Manufacturing tools, machinery, and mate- rials introduce a vast, complex set of subjec- tive variables for which the manufacturer must adjust to match the manufactured part feature to the absolute dimensional design data points. But since perfection in manufacturing is nearly impossible to achieve, the challenge for the manufacturer is to know how far a processed Keeping Your Design on the Road Target Condition Feature Column by Kelly Dack, CIT, CID+ Figure 1: Two drill data files.

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