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98 DESIGN007 MAGAZINE I JANUARY 2022 Article by Anaya Vardya AMERICAN STANDARD CIRCUITS Introduction One of the biggest challenges facing PCB designers is in not understanding the cost driv- ers in the PCB manufacturing process. is article is the latest in a series that will discuss these cost drivers (from the PCB manufactur- er's perspective) and the design decisions that will impact product reliability. Design Guidelines A standard recommendation is that all pad- to-trace intersections be tear-dropped when- ever the pad diameter minus the plated hole diameter is less than 0.020". is will increase interconnect reliability on the signal layers is process is designed to provide addi- tional metal at the critical junction of a pad and a run (trace). When an order is drilled and mis-registration occurs, it has been theorized that a long-term reliability issue can arise if the mis-registration occurs at the junction of the DFM 101: Signal Layers pad and the trace. Adding metal at this loca- tion helps ensure that an adequate connection is made and maintained. e tear-dropping process involves adding secondary pads at the junction of an existing (primary) pad and a circuit run. ese secondary pads are sized 0.002" smaller than the primary pads, and the center is placed 0.003" away from the center of the primary pad. is tooling is conducted using IPC standards for tear-dropping and has proven to be highly reliable and effective. Internal Power/Ground Layers • Provide a layer number and description on the artwork • Clearance pads must be a minimum diameter of 0.020" larger than the nominal finished hole size • When placing thermal pads, size the outside diameter using this formula: OD = FHS + 0.020" Minimum: OD = ID + 0.010" • Rotation of thermals and addition of spokes is customer dependent

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