The CC2340R5, along with the RF matching network and antenna, requires a large copper pour on the bottom layer of the board to provide a low impedance path to ground. In a two-layer design, this means that mainly only the top layer is available to route signals to and from the CC2340R5. Take care to make sure that the necessary bypass components are still placed as close to the IC as possible. Multiple vias underneath the CC2340R5 provide a low impedance path to ground for the device. Figure 4-1 shows the CC2340R5 WCSP footprint and wiring on the flex PCB.

Remember to consider the width of the signal traces to the balun and RF antenna in two-layer design cases. With the most rigid PCBs, it is often possible to find reasonable width traces that provide matching to design impedances. In the case of a 2-layer design, the thickness of the board, the PCB design rules, and the desired cost of the boards limits the maximum characteristic impedance of these traces. If matching is not possible, TI recommends keeping these traces as short as possible. Additionally, a pi-type matching network using 0201 footprints was left to allow matching with lumped elements. Perform RF impedance matching with the patch adhered to the skin of a wearer to emulate the environment of use.

Figure 4-1 CC2340R5 Routing on 2-Layer Flex Patch With Ground Plane Shown in Blue