General Design Considerations

Table 1. General Design Considerations
Thermal
1	The proximity of ground vias must be close to each ground pad of the module.
2	Signal traces must not be run underneath the module on the layer where the module is mounted.
3	Have a complete ground pour in layer 2 for thermal dissipation.
4	Have a solid ground plane and ground vias under the module for stable system and thermal dissipation.
5	Increase the ground pour in the first layer and have all of the traces from the first layer on the inner layers, if possible.
6	Signal traces can be run on a third layer under the solid ground layer, which is below the module mounting layer.
RF Trace and Antenna Routing
7	The RF trace antenna feed must be as short as possible beyond the ground reference. At this point, the trace starts to radiate.
8	The RF trace bends must be gradual with an approximate maximum bend of 45° with trace mitered. RF traces must not have sharp corners.
9	RF traces must have via stitching on the ground plane beside the RF trace on both sides.
10	RF traces must have constant impedance (50-ohm Coplanar or microstrip transmission line).
11	For best results, the RF trace ground layer must be the ground layer immediately below the RF trace. The ground layer must be solid.
12	There must be no traces or ground under the antenna section.
13	RF traces must be as short as possible. The antenna, RF traces, and modules must be on the edge of the PCB product. The proximity of the antenna to the enclosure and the enclosure material must also be considered.
14	BDE recommends using double-shielded coaxial RF cable to connect with the U.FL connector with antenna if the U.FL variants are selected.
15	Do not place or run the RF cable right above or below the module.
16	If there are some other radios besides this module in the system, try to place them apart as far as possible. And ensure there is at least 25 dB isolation between the antenna port of every radio.
Supply and Interface
17	The power trace for VDD_3V3 is recommended to be at least 20-mil wide.
18	The VDD_1V8 trace is recommended to be at least 20-mil wide.
19	Make VDD_3V3 and VDD_1V8 traces as wide as possible to ensure reduced inductance and trace resistance.
20	If possible, shield VDD_3V3 and VDD_1V8 traces with ground above, below, and besides the traces.
21	SDIO/SDMMC signals traces must be routed in parallel to each other and as short as possible (less than 12cm).In addition, every trace length must be the same as the others. There should be enough space between traces-greater than 1.5 times the trace width to ensure signal quality, especially for the CLK trace. Remember to keep these traces away from the other digital or analog signal traces. It is recommended adding ground shielding around these buses.
22	SDIO/SDMMC and digital clock signals are a source of noise. Keep the traces of these signals as short as possible. If possible, maintain a clearance around them.

Thermal

1

The proximity of ground vias must be close to each ground pad of the module.

2

Signal traces must not be run underneath the module on the layer where the module is mounted.

3

Have a complete ground pour in layer 2 for thermal dissipation.

4

Have a solid ground plane and ground vias under the module for stable system and thermal dissipation.

5

Increase the ground pour in the first layer and have all of the traces from the first layer on the inner layers, if possible.

6

Signal traces can be run on a third layer under the solid ground layer, which is below the module mounting layer.

RF Trace and Antenna Routing

7

The RF trace antenna feed must be as short as possible beyond the ground reference. At this point, the trace starts to radiate.

8

The RF trace bends must be gradual with an approximate maximum bend of 45° with trace mitered. RF traces must not have sharp corners.

9

RF traces must have via stitching on the ground plane beside the RF trace on both sides.

10

RF traces must have constant impedance (50-ohm Coplanar or microstrip transmission line).

11

For best results, the RF trace ground layer must be the ground layer immediately below the RF trace. The ground layer must be solid.

12

There must be no traces or ground under the antenna section.

13

RF traces must be as short as possible. The antenna, RF traces, and modules must be on the edge of the PCB product. The proximity of the antenna to the enclosure and the enclosure material must also be considered.

14

BDE recommends using double-shielded coaxial RF cable to connect with the U.FL connector with antenna if the U.FL variants are selected.

15

Do not place or run the RF cable right above or below the module.

16

If there are some other radios besides this module in the system, try to place them apart as far as possible. And ensure there is at least 25 dB isolation between the antenna port of every radio.

Supply and Interface

17

The power trace for VDD_3V3 is recommended to be at least 20-mil wide.

18

The VDD_1V8 trace is recommended to be at least 20-mil wide.

19

Make VDD_3V3 and VDD_1V8 traces as wide as possible to ensure reduced inductance and trace resistance.

20

If possible, shield VDD_3V3 and VDD_1V8 traces with ground above, below, and besides the traces.

21

SDIO/SDMMC signals traces must be routed in parallel to each other and as short as possible (less than 12cm).In addition, every trace length must be the same as the others. There should be enough space between traces-greater than 1.5 times the trace width to ensure signal quality, especially for the CLK trace. Remember to keep these traces away from the other digital or analog signal traces. It is recommended adding ground shielding around these buses.

22

SDIO/SDMMC and digital clock signals are a source of noise. Keep the traces of these signals as short as possible. If possible, maintain a clearance around them.