JLCPCB dielectric constant

[veeti]

Hello

Have people used JLCPCB for 6Ghz designs? I have understood that fr4 dk changes quite much over freq range. But they don’t offer anything else. I contact them but i only got  FR-4 dk @ 1MHz for response.

Or does someone have good alternative place to suggest - i only have used OSHPark.

br. Veeti

[eb4fbz]

FR4 Er not only changes with frequency, but also between manufacturers and batches. FR4 is just Flame Retardant type 4, which means it's a laminate made of woven glass reinforced epoxy resin. What weave design? How much epoxy? How much glass fiber? Who knows!

At high frequency, the losses are high and the weave makes the Er not constant along the surface. Better ask for 7628 and avoid 106 or 1080 weaves.

There are some better "premium" FR4 type laminates for RF. But your stackup must use cores on the RF layers instead of prepeg. RF layers are commonly routed on outer layers, and 4 layer boards are usually made of one core and two prepegs. You would have to use a 2 or 6 layer PCB, or order a custom stackup to have advantage of these laminates.

You can ask for controlled impedance too, but cost increases, and the high loss tangent is unavoidable. For certain applications it's sort of ok for 50ohm lines up to 6GHz, but forget about microstrip filters or impedance matchings.

[bd139]

PCBway will do Rogers laminate which has better defined microwave characteristics. I’ve never played with it though (yet)