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Page 98 of 131

JANUARY 2022 I DESIGN007 MAGAZINE 99 • Preferred set: rotate each thermal 45° to the plane and add spokes that are 90° apart • Spoke width: Preferred: 0.010" Minimum: 0.006" • To prevent exposed copper at board edge of routed panel, keep copper 0.010" away from the PCB's perimeter • Minimum barrel of hole-to-copper spacing: 0.008" • To prevent exposed copper at board edge of scored panel, keep copper at 0.025" away from PCB's perimeter Internal Signal Layers • Preferred trace/space: 0.004"/0.004" • Minimum trace/space: 0.003"/0.003"" • Inner signal layers must have a positive polarity • Clearly label layer number and description • Minimum barrel of hole-to-copper spacing: 0.008" • No thieving smaller than a 0.030" feature size is allowed • Relieve all copper internal to part from route paths by at least 0.010" • Provide thieving inside all open and breakaway areas, if permitted by the customer Outer Layers • Preferred minimum trace/space: 0.004"/0.004" • Minimum trace/space: 0.003"/0.003" • Keep all pad edges at least 0.050" from gold features or they will be gold plated • On the solder-side, leave a 0.200" x 0.400" area to add a date code box, ID, UL logo and cage code, etc. • Layout of circuitry on the board has a major influence on the way the panel actu- ally electroplates; try to avoid unbalanced copper area on the outer layers. Solitary traces will over-plate, while isolated holes will over-plate to yield finished hole sizes under specifications • To maximize plating distribution, allow the fabricator to add square thieving to low-density areas on the outer layers (such as breakaways or substantial unused spaces within the PCB) • For boards with edge connecters, there must be at least 0.050" of soldermask between the soldermask clearance of the nearest via hole and the top of the edge connector area; if this spacing is violated, mask will be extended onto the edge con- nector until 0.050" is achieved Understanding the cost drivers in PCB fab- rication and early engagement between the designer and the fabricator are crucial elements that lead to cost-effective design success. Fol- lowing your fabricator's DFM guidelines is the first place to start. DESIGN007 Anaya Vardya is president and CEO of American Standard Circuits and an I-Connect007 columnist. To contact Vardya or read past columns, click here. Additional content from American Standard Circuits: • The Printed Circuit Designer's Guide to… Fundamentals of RF/Microwave PCBs by John Bushie and Anaya Vardya • The Printed Circuit Designer's Guide to… Flex and Rigid-Flex Fundamentals by Anaya Vardya and Dave Lackey • The Printed Circuit Designer's Guide to… Thermal Management by Anaya Vardya • RealTime with… American Standard Circuits, three discussions: flex and rigid flex PCBs by Anaya Vardya and Dave Lackey; RF/microwave PCBS by Anaya Vardya and John Bushie; and thermal management by Anaya Vardya, John Bushie, and Dave Lackey • You can also view other titles in our full I-007e Book library here.

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