One method to transition controlled impedance lines from layer to layer is 
to form a coaxial line where the center via is your transmission line 
which is then surrounded by a ring of ground vias. Ground via diameter is dictated
by the dielectric constant of your substrate material.



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 \_   Mike McNulty             \_
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does anyone have any data concerning 50 ohm transmission lines
starting on the first layer and using vias to transport it to an inner layer.
I have looked at the IPC specs concerning microstrip etc.  good info.
unfortunately it just doesn't mention anything about how to get a 
impedance controlled line from one layer to the next.  I know that 
someone out there has done the numbers or knows where to go to
get them.  Please let me know 

thanks in advance.