Which stackup to choose for JLPCB FR4 up to ~10GHz

Question

I am aware that 10GHz on FR4 is not ideal, but this is an hobby project and I can tolerate some losses. The 10GHz on the PCB is minimal (probably only a short coplanar waveguide or microstrip with 2 passive components to an SMA connector).

I am planning to have the PCB (4 layer) manufactured at JLPCB controlled impedance service. When reading some discussions on the internet, many use the JLC7628 stackup. It seems to me I can better use the JL3313 stackup.

• 3313 lower Er (4.05 vs 4.6 for 7628)
• 3313 thinner prepreg between top layer and inner layer (0.0994mm vs 0.2104mm for 7268)

Calculated tracewidth for 3313 is quite narrow ~0.15mm vs ~0.3mm for 7268.
0.3mm is easier to match to a 0.3mm SMA connector pin, which I consider an advantage in favor of the 7268.

Any suggestions/experiences here which route to go ?

Answer 1

It really depends on the material of the PCB. If you just went with Isola FR408 YMMV because the dielectric constant might vary from your calculations of the design

Here is an example that a user posted of 60mm lines 6GHz on FR4 from Oshpark. You'd expect about a -3dB loss at 10GHz if you assume the graph is linear.

Source: https://www.eevblog.com/forum/rf-microwave/9-10ghz-and-fr4/

If that doesn't work then I'd probably go with another material that has better dielectric constant specs like a rogers material (expensive) or another material:

• PPE and PPO resin – it’s a suitable option for 1-10GHz frequencies. These secure an excellent all-round performance of your PCB.
• Modified epoxy resin – these are an excellent choice for frequencies between 1GHz and 10GHz. Generally, they are affordable and a reason as to why they are so popular. Source: https://www.ourpcb.com/pcb-materials.html