When you are playing with circuits having nano to pico second rise times then PCB track size, shape and spacing affect the circuit performance both as intended and as a "transmitter".
The days of the PCB layout just being a matter of squeezing all the bits into the available space have long gone. If you are designing products intended for use in the European Union, then I suggest you have a good look at the EU
EMC Directive and the associated generic harmonized standards for emission and immunity.
If you want to discuss this further, I am happy to assist.
Dave Hoover wrote:
> I'm fairly new to this group and really enjoy
> absorbing as much as I can from here. Being as
> I'm from the PCB fab side, I'm always tantalized
> (YANKED) into the electrical properties side
> of circuits/PCBs. Now I have a question.
> I have a customer (phone card manufacturer) who
> indicates that teardropping trace to pad junctions
> increases the the capacitance enough to completely
> change his EMC characteristics of the trace.
> Can this be so? (Sanity Check time)
> Next, there was ground pours around pads that had
> an octagon shape. We contourized the clearance which
> made it circular. Can this do the same EMC impact?
> In an industry where I've always been told that for
> reliability reasons we should always do the above
> mentioned for DFM. Now......in an RF environment the
> same reliability things change the designed in
> characteristics? I'm lost..........
> Any and all responses will be greatly appreciated.
> David Hoover
> Field Application Engineer
> McCurdy Circuits
> (714) 974-0401 ext 34
> (714) 974-3596 fax
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