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Design007-July2021

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JULY 2021 I DESIGN007 MAGAZINE 63 locations, etc. It's up to the engineering team to confirm with the supplier what is expected, what is acceptable, and what is agreed upon to produce and deliver a PCB at the required level and quality. We don't want the supplier to have to make assumptions or guess, and a good supplier will not do so anyway. Instead, a good supplier will hit you with a "technical query," while your job is stopped and placed in a hold- ing pattern, until you clarify any concerns from the supplier. Cherie Litson: You obviously think that the fab- ricator can follow your outline somehow. Only if you send them a route file will they be able to do that. You need to have dimensions and tolerances on those dimensions and notes so that the board can be built and checked prop- erly. If not, then you get what you get, which will probably not be quite what you wanted. Gerbers are stupid camera "open, draw, close" files, and they are only for exposing what cop- per to keep. ey are effective for the copper, but not for a board edge. (ere's no copper there, or should I say, there shouldn't be.) Having a dimensioned drawing helps to clar- ify any misinterpretation of the files you are sending, even if you're sending ODB++ or IPC-2581 files. ere have been many times where I missed checking a box in the output soware and things got crossed up. When fabricators had a picture of what my inten- tions were, they could contact me if there was a mismatch. Carl Schattke: e short answer is no, they are not required. Long answer: ere are a few reasons to be more specific in our documenta- tion. I like to have a layer reserved for the board routing profile. is can be imported and used by the manufacturer. Adding dimensions lets the manufacturer know that they are doing this right, and they can check the value. Also, add- ing dimensions lets incoming inspection at the PCBA vendor check to make sure the routing was done correctly and that the image is regis- tered to the board outline properly. You have to add the dimensions needed so that they can be checked if you don't want to have that be a possible failure mode. Rick Hartley: When dimensions on the drawing match the information in the electronic files, this tells the fab and assembly people that we are paying attention and gives them a better sense of confidence that all the dimensions are correct. Are they strictly needed? No, but they can be helpful. Lee Ritchey: Yes, it is vital to dimension a PCB on the fab drawing. How else will a fab- ricator determine how to bid on it? Gerber data is rarely given to a fabricator until a P.O. is issued. DESIGN007

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