Should Pin 21 of BLUENRG-M2SA be grounded?

[ASang.2]

Hello,

I am using the BLUENRG-M2SA in my design. In the BLUENRG-M2 datasheet at https://www.st.com/resource/en/datasheet/bluenrg-m2.pdf, it is stated that all GND pins must be grounded. However, in the BLE module integration design guidelines (DT0142) at https://www.st.com/resource/en/design_tip/dt0142-ble-module-integration-design-guidelines--stmicroelectronics.pdf, it is recommended to leave the top portion of the module overhanging the edge of the PCB, which will make it impossible to connect Pin 21 of the BLUENRG-M2SA to GND.

I am really confused by the 2 contradictory statements in these documents. Which one should I follow:

1. Connect Pin 21 to GND, which means that the module cannot overhang the edge of the PCB - or -
2. Do not connect Pin 21 to GND and leave the module overhanging the edge of the PCB

Any guidance would be appreciated.

Thank you

[Winfred LU]

Connect Pin 21 to GND.

If antenna cannot be mounted in an overhanging position, then the followed guidelines must be made to keep area clear of copper:

1. Never place the ground plane or route copper traces directly underneath the antenna portion of the module
2. Never place the antenna close to metallic objects
3. Keep wiring, components, and objects away from antenna
4. Do not place the antenna in a metallic or metalized plastic enclosure
5. Enclosure walls should be 1 cm or more away from the antenna in all directions

as recommended in Figure 3:

 

[AGoss.1]

Hello,

It's STEVAL-IDB008V1M

Under BLUENRG-M2SA is copper with VIAs.

Is it normal?

Note:

• All unused pins should be left floating; do not ground

• All GND pins must be well grounded

• The area around the module should be free of any ground planes, power planes, trace routings, or metal for 6 mm from the module antenna position, in all directions.

• Traces should not be routed underneath the module 

[ASang.2]

Yes. It is normal.

• The area around the module should be free of any ground planes, power planes, trace routings, or metal for 6 mm from the module antenna position, in all directions.

This is about the area around the module antenna. There should be not copper 6mm from the antenna position.

• Traces should not be routed underneath the module 

Vias are not traces. The vias just stitch the ground planes together.

Thank you

[SPhil.3]

I'm not sure if the discrepancy between the recommended keep out area in Figure 3 and the evaluation board (STEVAL-IDB008V1M) layout in Figure 4 of the DT00142 BLE module integration design guidelines was properly answered.

The 6th bullet under the basic guidelines says, "Add an uninterrupted ground plane on host board, directly underneath the top shielded zone of the module."  The note in Figure 3 then indicates that there should be no components or copper on any layer 6mm from the top edge of the BlueNRG-M2 module.  The BlueNRG-M2SA evaluation board floods all layers under the entire module with ground.  This is in direct contradiction with the note in figure 3.

On my layout (see photo below), I removed copper from any layer 6mm from the edge of the the BlueNRG-M2SA module.  This has the ground plane starting at about pins 2 and 18 on the module.

 Should the layout match the guidelines or the evaluation board layout?

Thanks for your assistance -