4- Layer High-Frequency PCB with FR4 & Rogers Hybrid Lamination

Recently, KnownPCB has completed a 4-layer high-frequency PCB project with FR-4 and Rogers materials hybrid lamination structure.

This multilayer hybrid high-frequency board supports both high-speed signals and general functional circuits, it should ensure the electrical performance and the design of this hybrid high-frequency PCB must also consider the stability of manufacturing and cost control at the same time.

Therefore, the hybrid lamination technology is the critical part in this high-frequency PCB fabrication.

About this hybrid structure high-frequency PCB:

	Base Material	FR-4 + Rogers
	Layers	4
	Dimensions	-
	PCB Thickness	1.69mm
	Board Solder Mask Color	Green
	Silkscreen	White
	Surface Finish	ENIG

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4- Layer High-Frequency PCB with FR4 & Rogers Hybrid Lamination

How to achieve both high-frequency performance and manufacturing reliability on FR4-Rogers hybrid PCBs?

In the design of high-frequency circuit board, Rogers materials have a dielectric loss and stable electrical performance, and can be applied to critical high-frequency signal areas. And FR-4 materials prossess a good machinability and cost advantages, it is suited for non-RF regions.

For more comparison between Rogers and FR-4, please read Rogers® vs. FR-4 Materials

As the result, by using FR4-Rogers hybrid lamination, a high-frequency PCB can achieve an optimal balance between high-performance and cost control.

However, due to the differences in dielectric constant, coefficient of thermal expansion (CTE) and mechanical performance between FR-4 and Rogers, the difficulty of stackup design and manufacturing control of a high-speed and high-frequency is significantly increased.

The manufacturing risks of high-frequency PCB with hybrid materials：

1. The differences in material CTE will result in PCB warpage (bow and twist) and distortion.

Learn more about PCB warpage

2. It is difficult to control interlayer bonding strength, which can lead to the risk of PCB delamination.

3. Tolerance deviation of dielectric thickness will affect the stability of impedance.

4. In the multilayer high-frequency structure, layer-to-layer misalignment will be amplified and have impact on the performance consistency of overall RF circuit board.

In order to avoid the risks above, KnownPCB have made manufacturing solutions for this multilayer high-frequency PCB with hybrid materials as below:

1. PCB warpage that caused by CTE differences:

During the pre-prduction stage, KnownPCB reviewd the CTE of FR-4 and Rogers materials. By controlling and optimizing the lamination temperature, pressure and thermal cycling curves, we have reduced the accumulation of internal stress between FR-4 and Rogers, and the risk of this RF board warpage.

2. Insufficient interlayer bonding force:

According to material characteristics, we have choosed suitable bonding solutions and lamination parameters to ensure a stable bonding between FR4 and Rogers materials.

3. The influence of dielectric thickness:

In the DFM review, KnownPCB has controlled the thickness of critical high-frequency layers and optimized material distribution based on impedance requirements, so as to ensure superior and stable transmission performance of high-frequency signals.

4. Multilayer interlayer misalignment

We have reduced the offset effects that caused by material expansion and contraction through engineering compensation, lamination control and high-precision alignment management.

Final Result

The 4-layer high-frequency PCB with hybrid FR-4 and Rogers materials has achieved stable transmission of high-frequency signals, and at the same time has prossessed good electrical performance and long-term mechanical reliability.