Questions on 5.8GHz PCB layout

Dear all,

I have got some questions on 5.8GHz PCB layout with Rogers material.The first one is that should i use microstrip line or CPG for RF lines? And the second one is that can i use solder mask or not?Even for gold-plating?

Please avvise and tell why, thanks!

At your frequency you can prototype on FR4 with or without solder mask and afterwards move to Rogers. If you will use Rogers it just be easier to get right dielectric constant, but more expensive. In your case i would use microstrip lines and solder mask.
By CPG what do you mean? Coplanar guide? I can't see how it helps. Maybe to reduce radiation losses. But Rogers is already have very low loss, so coplanar guide effect seems to be neglible relative to good substrate loss. Maybe on some thick FR4 coplanar guide will make difference.
About solder mask. There was a topic here, about trying to simulate solder mask effect. Conclusion was solder mask effect is neglible up to 20GHz or so, and simulating it makes no sense as solder mask thickness varies even on a single PCB, and also there is thickness jump along copper edges. And at 5.8GHz it must be very long line to make some shift in phase.
About gold-plating, i have seen some PCBs where gold-plating without green mask was destroyed, maybe by enviromental conditions or wrong plating manufacturing process, but still worked ok.
Also, i asked one time about manufacturing on RO4003, and was given an anwer that there is only gold plating available, and they explained that tin plating can damage copper layer somehow, bent or something. Although i have seen PCB on RO4003 with tin plating.

i have NEVER had good luck at 5.8 GHz with FR4. I would recommend a thin rogers or other microwave material.

For short runs, like chip to chip, microstrip is fine. For longer runs, CPG is better, because it radiates a whole lot less

Thank you sir, my TRx line is short and Tx power is not high, then maybe ustrip line is ok by your advice,thanks.



HI Sir,

Thanks for the detailed advice.I'll use Rogers' 4350(dielectric constant is 3.48)for the prototype and use ustrip line,gold-plating or solder mask is to be decided.