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Features of PCB Design for STM32WB

Microwave tracing of printed circuit boards must be carefully worked out. Let's consider the main aspects of PCB design for STM32WB. Let's start with impedance matching. It is known that to reduce signal reflection it is necessary to match the impedance of the source, receiver, and transmission line.

The impedance of a transmission line depends on its geometry and the location of the supporting surface. By the reference surface, I mean a conductive layer with zero potential, the geometrical dimensions of which significantly exceed the dimensions of the conductive line. Let's list the main factors influencing the wave impedance of the transmission line:

• Line type: microstrip, strip, coplanar

• Line width

• Distance to the support layer H (dielectric thickness).

• Dielectric material parameters (dielectric constant)

• The thickness of the conductive layer, which is more influenced by the thickness of the conductor T1, to a lesser extent by the thickness of the copper of the reference layer T2;

• Solder mask thickness

The impedance of a transmission line depends on its geometry and the selected PCB layer stack. Depending on whether the priority is stack or geometry, there are two approaches to design. The first approach is that the developer of the board sets the geometric dimensions of the conductors convenient for him, and then selects the layer stack and production technology for them. However, it is far from always possible to find the required stack within the technological limitations of the PCB manufacturer.

A situation may arise in which even if the manufacturer is able to produce a board on a given stack, its cost will be much higher than the typical one, especially when it comes to a small series or a prototype. Another approach is to select a generic stack from the manufacturer.

Each PCB manufacturer has recommended solutions, the use of which ensures the minimum production cost. But in this case, you will have to select the geometry of the transmission lines for the available parameters, and this does not always suit the developer. Both approaches require the developer to work closely with the manufacturer.