Issue link: https://iconnect007.uberflip.com/i/1512857
38 DESIGN007 MAGAZINE I DECEMBER 2023 Geometric interference: In terms of a PCB design, this is a condition in which a mechani- cal feature on a finished PCB could come into unwanted contact with a significant counter- part, thereby affecting further assembly or elec- tromechanical performance. Geometric dimensioning and tolerancing (GDT), as covered in the pages of ASME Y14.5 and IPC-2615, is easy to understand if you speak the language. So is Mandarin. How- ever, there is a void in the PCB design industry when it comes to conveying what is required on fabrication drawings for PCB outlines. It seems that those who speak and document PCB dimensioning and tolerancing have little patience for those who do not. e apparent state of PCB dimensioning and tolerancing knowledge in the industry is likened to the state of the city of Babel where the language is confused. ere is an elephant in our indus- try's inspection room, and it is not backed up against three mutually perpendicular datum planes. ere are dozens of process steps a PCB goes through before completion. One of the final steps is to de-panel or excise a PCB assem- bly from its supporting panel structure so it can move on to its next assembly level where it must fit well. Can you imagine building and shipping a thousand simple PCB assemblies to a final assembly plant and getting a message Target Condition Feature Column by Kelly Dack, CIT, CID+ Designing Unconventional Geometries