Recommended PCB Stack-up for BALFHB-WL-02D3

[MoralkaraLynn]

My team and I have been working on the design of a radio module using the STM32WLx5 MCU. To simplify the RF front end, we decided to go with the BALFHB-WL-02D3.

In the BALFHB-WL-02D3 Datasheet, the below mentioned board stack-up is recommended for the best RF performance. This stack-up comes up to a 1.085mm board thickness (which is non-standard)

We had a few questions on the stack-up:

• Our local manufacturer had some issues while manufacturing the desired board thickness. What would be the effect on the RF performance if we were to use a standard 1mm / 1.2mm board thickness (details below)?

• We are also looking forward to using the Rogers PCB Substrate (RO4003C, RO4350B etc). As the dielectric constants of FR4 and RO has a drastic difference, the RO board stack-up should be significantly different. What would be the dimensions if we were to use a Rogers Laminate as the Prepreg?

Thanks,

MoralkaraLynn

[BenoitB]

Hello Moralkara,

With BALFHB-WL-02D3, Total thickness is not important effect on the performance. The important parameter to respect in the stack up is the thickness of the dielectric2 (it is necessary to be close 0.160mm) between top layer and first ground inner layer.

The second stack may be suitable because the two prepregs are approximately 0.150mm

On your stack up, we don’t see inner layers. Do you have inner layers?

It is important to respect the layout of the datasheet and to have a ground plane under the BALFHB-WL-02D3 on the first inner layer with dielectric2 around 0.160mm.

Please find all CAD resources information associated with BALFHB-WL-02D3 to obtain the layout and associated BOM recommendation with this link:

STDES-WL5U4IHH - 4-Layer Reference design based on IPD "BALFHB-WL-02D3" with STM32WL UFQFPN MCU - High Band - High Power - STMicroelectronics

Don't hesitate if you need more information

Best Regards

Benoit Bonnet