Issue link: https://iconnect007.uberflip.com/i/1500943
36 DESIGN007 MAGAZINE I JUNE 2023 the part is guaranteed to fit and function with other mating parts in the next assembly. PCB fabrication and assembly drawings are still the common means to communicate toler- ances. ere has been much headway in doc- umentation automation. But with next-gen- eration PCB designers entering the industry without training, we are now seeing automati- cally output PCB drawings missing the very specifications that they are intended to convey. Long ago, PCB designers learned the founda- tional aspects of the trade as a branch of a more in-depth design draing program offered by community colleges. ese programs helped teach the language of engineering: documen- tation concepts (including geometric con- struction), third-angle projection, ANSI stan- dard drawing practices, and the fundamental aspects of geometric dimensioning and toler- ancing (GDT), to name just a few. With very few of these school programs available to teach the documentation process, manufacturing engineers are oen le scratching their heads while trying to quote or produce a PCB. CAD tool suppliers have done only half the job by evolving capabilities to perform draing and documentation. As in all things, capability without under- standing can be as dangerous. e industry continues to see an onslaught of documenta- tion output by new designers who are "running with scissors." Now, with auto-dimensioning capability, we are seeing dozens of unneces- sary dimensions added to parts inappropri- ately, causing double-dimensioning night- mares. We see auto-generated PCB stackup details embellished with laminate attributes which were clearly not understood by the designer and cannot be produced. Who will finish educating our designers on how to wield these tools? Global Autonomous Design and Manufacturing Still a Distant Vision In driving school, we learned that the prima facie speed limit means, "Do not drive faster or slower than conditions permit." Always safely adjust for the surrounding conditions. Anyone who designs a PCB must be in touch with the prima facie limits of manufacturing specifica- tion and tolerance capability. Our industry continues to preach this prima facie concept through DFM. But this concept has become so subjective it is rendered meaningless to our global manufacturers. How can designers incorporate DFM if they don't know the pro- duction supplier or manufacturing capabili- ties? PCB designers are the last to know where in the world their design may be produced as it scales to volume. Free DFM reviews by onshore prototyp- ing services read much differently than DFM reviews from China, Ireland, India, or Viet- nam. Adjusting a CAD tool's DRC settings to consider every supplier's unique manufactur- ing limitation in hope of achieving DFM is a distinct challenge. It seems global suppliers are unwilling to share their limitations unless you send business to them. So, what are the options? Top DFM 'Speeding Tickets' Issued by Suppliers • Failure to provide design geometry to meet IPC-6012 manufacturing process and class specification • Failure to provide tangible dimensions and tolerances defining form, fit acceptance criteria • Failure to provide IPC-D-356 netlist (ODB++ is not utilized sufficiently offshore) • Failure to declare copper thickness specification as "base" or "finished" • Failure to locate an intelligent design origin relevant to the PCB such as a mounting hole • Failure to allow for generic laminate material substitution Where can an inexperienced designer learn more? IPC holds PCB design classes, such as