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26 DESIGN007 MAGAZINE I AUGUST 2020 Feature Interview by the I-Connect007 Editorial Team Editor's note: When this interview was con- ducted, Mark Thompson, CID+, was in engi- neering support at Prototron Circuits. Mark is now a senior PCB technologist with Monsoon Solutions, a design and engineering bureau in Bellevue, Washington. In his position in the CAM department at Prototron Circuits, Mark Thompson has seen his fair share of puzzling data and documenta- tion. He discusses some of the difficulties he's encountered with designers' fab notes and provides designers with a number of points to consider the next time they send out a design. Andy Shaughnessy: Mark, give us a taste of some of the more common problems you see with customers' fab notes. Mark Thompson: From where I sit as an engi- neer in a fabrication environment, the big- gest thing I see is designers who produce boiler- plate notes that they get from their CAD system. A lot of them have templates Mark Thompson's Most Wanted: Accurate and Complete Fab Notes that are already embedded in their system. They can just call it up and say, "Notes 1–14 are golden. We're going to put those on." Ultimately, if it doesn't have anything to do with the job, get rid of it because it's going to cause additional grief and phone calls from the fabricator. There is some information that your fab notes should absolutely have, including standards, a board class, and material type. Flatness is another; if flatness is critical, put in tolerance for flatness. If it's a board that is massively dielectrically challenged, with very thin dielec- trics on one side and very thick dielectrics on the opposing side, whether you add additional metal on the outside or one is a solid plane and one is a full signal, it can still end up with some modicum of warpage. Warpage being an issue, flatness is a callout that you're going to want to have in your drawing. We also need hole tolerances, dielectric thick- nesses, shape tolerances, and the overall board dimensions (is it 4" x 5"?), as well as surface finishes, immersion gold, immersion silver, deep gold, or HASL. All of the surface finishes have a tolerance and a thickness based on IPC standards that need to be adhered to. That's

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