Routing High-Speed differential signals on top and bottom?

Hi,

I plan to design aboard with 10 Gbps (~35 ps rise/fall time) transceiver.

TI High-Speed InterfaceLayout Guidelines recommend:

(http://www.ti.com/lit/an/spraar7e/spraar7e.pdf)

"When possible,route high-speed differential pair signals on the top or bottom layer of thePCB with an adjacent GND layer. TI does not recommend stripline routing of thehigh-speed differential signals.".

 

Do you think this is agood rule of thumb?

On one side this willavoid via stubs, on the other hand the signal goes to the full via lenght (inmy case 60 mil) which will cause more insertion loss compared to a short via to the next signal layer.

 

Assumed that you have enough space to route only on top and bottom:

Are there otherdisadvantages when using stripline routing / advantages of microstrip line routingthat can explain this recommendation? 


thank you for your feedback

Christian

MegaOhm 4 years 18 days

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Answered byOld_School 4 years 5 days
Hi MegaOhm,

  Low pin out connectors (USB2.0) and ICs (TQFP48 packages) can be easily routed on only 1 surface layer.  

  Yes, routing with only top layer from the IC pin to connector pin surface mount will produce the best possible RF performance.  If vias must be used they should be either back drilled or laser micro via spanning 1 to 2 layers to minimize via stubs.  You also need to cut back your GND plane by using larger anti-pad clearance to reduce the parasitic capacitance between your signal via and your GND plane.

Cheers!
OS