VIA shielding recommendation for 30GHz

Thread Starter

yef smith

Joined Aug 2, 2020
693
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.

1698779254885.png
 

Janis59

Joined Aug 21, 2017
1,819
General thumb-rule - lambda half means maximum linkage, lambda/4 means small linkage but measurable, lambda/10 - practically negligible linkage and lambda/40- not existent even theoretically, it works like the common one piece. For example - optical glass roughness - lambda quarter - the milk colour begin to clear, lambda/10 - for most of lenses good enough, lambda/40 - ideal for most demanding applications.
 

Thread Starter

yef smith

Joined Aug 2, 2020
693
Hello Janis59,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.
 

Janis59

Joined Aug 21, 2017
1,819
Look for the example in NRF025L application note. There for gnd-ing is used a countless series of rivets, some 20 or about so pieces. By the way, inductance is thing eay to calculate.
 

PadMasterson

Joined Jan 19, 2021
63
You didn't mention the Dielectric thickness or Dk but using a Megtron6 material and the Coplanar waveguide you showed, I used the Saturn calculator to come up with a few numbers.
1699033141945.png

Since the side plane fills are part of the RF path, your vias should be at a minimum of 1/4 wave length and depending on the size, I think if you can get them at .05" apart you should be OK. The pads of the vias can be tangent to the plane shape so you don't have bumps along the edges. The material used, copper thickness and Dk thickness will be factors also including any plating you might use. I would suggest silver plating if you want to use plating, at that frequency, I think ENIG is going to give you higher losses but lots of people use it. You can check with material vendors also, like Rogers for more information too. Good luck!
 
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