Low-cost high-frequency RF multilayers?
There's no such thing as "can't be done"!

As soon as RF materials become multilayer, many designers initially shy away from the high manufacturing costs that such designs traditionally entail. Leiton GmbH has therefore specialized in cost-effective hybrid solutions that only use expensive RF materials where they are actually needed. The rest remains a conventional FR4 multilayer and therefore cost-effective.

Laminar technique

In particular, pure RF prepregs are rare and expensive for many manufacturers. However, if you take a closer look at the RF requirements, it becomes apparent that such RF prepregs are not necessary at all. This is because the frequency-sensitive layers are often planned on top and bottom locations to the nearest inner layers. In conventional multilayers, prepregs and copper foil are used. But the so-called laminar technique makes it possible to press pure Rogers cores on the outer layers. Thus, no prepreg is necessary here and the required thickness can be freely selected according to the Rogers cores, e.g. from the standard Rogers 4000 series.

Stack-ups of up to 12 layers are not uncommon

Below or after these outer layer cores are conventional FR4 prepregs, which do not have good RF properties themselves, but no longer have RF relevance at these points in the structure. This is how Rogers FR4 hybrid bodies are created. As long as two coordinated RF layers are always followed by at least one layer without RF relevance, a setup can be varied as desired. Stack-ups of up to 12 layers are not uncommon. In order to counteract curvature, symmetrical superstructures are always preferred, but asymmetrical superstructures are also technically feasible if the developer accepts slight imperfections in terms of flatness.

In addition, many technologies from the field of rigid printed circuit boards can be implemented here with almost no restrictions. These include HDI requirements such as fine conductors, blind, buried, stacked or laser VIAs, as well as depth milling or DK slots and DK contours.

Examples for Rogers-FR4-Hybrid-Multilayer

4-Layer Hybrid Multilayer - 1,55mm Laminar Füllkern

5-Layer Multilayer Hybrid Roger RO4350B FR4 Laminar