4mil vs 8mil via

[ktr]

Hello, I am thinking the practical difference in using a 4 mil via vs 8 mil through hole, plated via in a standard 4-layer (RF-GND-PWR-GND) 62 mil (1.6mm) PCB board. Frequency is 1.4 Ghz. I know at higher frequencies via diameter becomes more important; however would there be a sizeable difference at L-Band ?

Kind Regards,

ktr

 

[thunderdantheman]

Unless you require extremely low S11 / S22 optimizing the vias will likely not have a huge effect within the L band. I would be trying to keep RF on a single layer though.. 4mil vias will likely cost more! Via dimensions are pretty hit and miss at high freq and don't really follow typical rules... really need an FEA EM tool to work it out. But that being said, by removing inner unused pads, back drilling, blind & buried vias, and or using HDI with microvias I've been able to meet (and exceed - ) compliance with PCIe3 and USB3 without such tools. Leaving the mid layer pads on coupling vias is argued to make them more capacitive hence lower impedance.. This makes sense.. but I've never tested it.