VIA shielding recommendation for 30GHz

[yefj]

Hello, I have a microstrip trace of width W1 as shown below, regarding other dimentions like W3 i need recomendations in wavelength units.
fo example W3=lambda/20
but regarding the recommended radius R the distance of the trace from shielding W2 , VIA from shielding W4.What do you recommend regarding these distances?
Thanks.

 

[BigBoss]

They must be as close as possible in according within MRC of the PCB manufacturer.

MRC: Manufacturability Design Rules.

 

[yefj]

Hello,what the VIA dimentions?

 

[volker@muehlhaus]

You can choose a small via diameter that is within manufacturing rules. Not critical.

 

[yefj]

Hello ,via diameter also plays a role,the bigger the radius the more capacitance the shielding VIA will have .
the longer the length the more inductive the VIA will be.
if my signal is at 35GHz, what LC (S-param)responce should the VIA be so my trace will be shielded properly?

 

[volker@muehlhaus]

Hello ,via diameter also plays a role,the bigger the radius the more capacitance the shielding VIA will have .

This is correct, but it also depends on spacing between the vias. If you want to be accurate, use EM simulation on your layout and adjust the line width for desired line impedance, at the given via size and spacing.

Otherwise, following your own logic from your statement above, you want to use vias as small as possible (within design rules) to reduce the influence on capacitance C'

the longer the length the more inductive the VIA will be.

That is less of an issue, because the via only connects top ground and side grounds, which are almost same potential due to all the vias combined.