Rogers | FR4 Hybrid | High Frequency | Cost Optimization

Rogers FR4 Hybrid Multilayer – Efficient PCBs with FR4 Cost Advantages

As soon as HF 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 HF materials where they are actually needed. The rest remains a conventional FR4 multilayer and therefore cost-effective.

Laminar technique

In particular, pure HF prepregs are rare and expensive for many manufacturers. However, if you take a closer look at the HF requirements, it becomes apparent that such HF 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 HF properties themselves, but no longer have HF relevance at these points in the structure. This is how Rogers FR4 hybrid bodies are created. As long as two coordinated HF layers are always followed by at least one layer without HF 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 impeHFections 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

FAQ

What Are Rogers Hybrid PCBs?
"Hybrid" refers to the use of different materials within a PCB layer stack-up, typically Rogers and FR4. In most cases, FR4 is used as prepreg to bond Rogers cores together.
What Are the Advantages of Rogers Hybrid PCBs?
A major limitation for the availability of Rogers multilayers is often the prepreg material. Due to limited shelf life, many manufacturers do not stock Rogers prepregs, restricting supplier options and increasing costs. If it is electrically feasible to use conventional FR4 prepregs, nearly all PCB manufacturers become viable suppliers, significantly reducing costs.
What Is Laminar Technology?
A standard 4-layer PCB is typically built with a 2-layer core in the center and pressed copper layers on the top and bottom (1+2+1). In laminar technology, two 2-layer cores are directly pressed together in the middle (2+2).
When Should Rogers-FR4 Hybrids Be Preferred?
The more cost-effective hybrid technology is particularly useful when controlled impedance or high-frequency performance is only required on or between the Rogers layers, while the FR4 layer has minimal impact on signal integrity.
What Are the Disadvantages of FR4-Rogers Hybrids?
Asymmetrical layer stacks can lead to slight warping due to different thermal expansion rates. Signal integrity is primarily limited to the pure Rogers layers.
What Prepregs Are Used in Rogers Hybrids?
Typically, FR4 prepregs (PP) are used because they offer higher availability and lower costs.
Are FR4-Rogers Hybrid HDI PCBs Available?
Yes, Rogers-FR4 hybrids can also be manufactured as HDI (High-Density Interconnect) PCBs. Options such as buried vias, blind vias, SBU (Sequential Build-Up), plated slots, and depth milling are fully possible.