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38 The PCB Design Magazine • October 2015 drill file. Either one of these can cause commu- nication delays. 7. Communicate With Your Fabricator ASAP In order to facilitate the best communica- tion, you need to meet with your chosen fab- ricator as soon as possible in the design cycle. Check with them for validation of any imped- ance you may have. Make sure these notes do not conflict either. Be sure to: Check for proper reference planes. Make sure impedance traces do not traverse multiple splits or lack ref-planes altogether. Dif- ferentiate between single-ended and differen- tial type structures by a tenth or a hundredth of a mil. Again, fabricators cannot resolve these small increments, but this allows the fabricator to uniquely select just the impedance tracks for any resizing that may be necessary to meet de- sired impedances. Make sure the space between differential pairs is consistent throughout the run. Allow for process deviation, setting up a part as .1 mm trace and space on half-ounce starting copper does not leave room for any trace resizing that may be necessary to meet the impedances if di- electric cannot be altered. When calling out materials, call out the 4101/# such as 4101/126. This will allow the fabricator to use any material that falls within the /126 criteria. Calling out a specific material may limit the pool of fabricators that can build the board. Avoid creating same net spacing vio- lations when terminating differential pairs, and do not "wrap" the differential pairs around the terminus. 6. Annular Ring must be Adequate and Communicated in Plans Make sure all pads for plated through-holes have sufficient annular ring. The general rule of thumb is .010" MIN larger than the FHS (finished hole size) for signals and .015" MIN for internal relief/antipads. For vias, you may want to specify +.003" /- the entire hole size. This tells the fabricator in no uncertain terms they are indeed vias and can be drilled smaller if necessary. 5. Check Your Edges For scored parts, do not pour metal any closer to the part edge than .015" for an .062" board, and at least .009" for an .031" thick part. 4. Check Your Drill Aspect Ratio If your drill aspect ratio is greater than 10:1, be sure to consult your chosen fabricator. 3. Communicate uncommon Materials If using an uncommon material type, make sure you call the chosen fabricator to make sure it is something they stock or can get quickly. 2. File Naming When exporting Image files avoid the use of control characters in the file names. And finally, the Number 1 thing to remember to help you streamline your design through fab process: 1. Consult Your Fabricator Be sure to consult your fabricator and dis- cuss any deviations you may require. Be spe- cific about any special needs for the part, such as extremely tight tolerances or additional edits necessary. This is the key to accelerating your design process. PCBDESIGN Mark Thompson is in engineer- ing support at Prototron Circuits. his column, The Bare (Board) Truth, appears bimonthly in The PCB Design Magazine. To read past columns, or to contact Thompson, click here, or phone 425-823-7000, ext. 239. the bare (board) truth SPEEDING uP THE DESIGN CYCLE: 10 THINGS TO REMEMBER " in order to facilitate the best communication, you need to meet with your chosen fabricator as soon as possible in the design cycle. "

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