AzureWave AW-NM288SM Guide

AW-NM288SM
I IEEE 802.11 b/g/n Wireless LAN Module
Layout Guide
Rev. 01
1
The information contained herein is the exclusive property of AzureWave and shall not be distributed, reproduced, or disclosed
in whole or in part without prior written permission of AzureWave.
Revision History
Document
Release
Date
Version 0.1
2016/08/26
Description

Initial Version
Initials
Approved
N.C. Chen
N.C. Chen
2
The information contained herein is the exclusive property of AzureWave and shall not be distributed, reproduced, or disclosed
in whole or in part without prior written permission of AzureWave.
INTRODUCTION
This document provides key guidelines and recommendations to be followed when creating AWNM288SM layout. It is strongly recommended that layouts be reviewed by the AzureWave
engineering team before being released for fabrication.
The following is a summary of the major items that are covered in detail in this application note.
Each of these areas of the layout should be carefully reviewed against the provided
recommendations before the PCB goes to fabrication.

GENERAL RF GUIDELINES

Ground Layout

Power Layout

Digital Interface

RF Trace

Antenna

Antenna Matching

GENERAL LAYOUT GUIDELINES

THE OTHER LAYOUT GUIDE INFORMATION
3
The information contained herein is the exclusive property of AzureWave and shall not be distributed, reproduced, or disclosed
in whole or in part without prior written permission of AzureWave.
1. GENERAL RF GUIDELINES
Follow these steps for optimal WLAN performance.
1. Control WLAN 50 ohm RF traces by doing the following:

Route traces on the top layer as much as possible and use a continuous reference ground
plane underneath them.

Verify trace distance from ground flooding. At a minimum, there should be a gap equal to
the width of one trace between the trace and ground flooding. Also keep RF signal lines
away from metal shields. This will ensure that the shield does not detune the signals or
allow for spurious signals to be coupled in.

Keep all trace routing inside the ground plane area by at least the width of a trace.

Check for RF trace stubs, particularly when bypassing a circuit.
2. Keep RF traces properly isolated by doing the following:

Do not route any digital or analog signal traces between the RF traces and the reference
ground.

Keep the balls and traces associated with RF inputs away from RF outputs. If two RF
traces are close each other, then make sure there is enough room between them to
provide isolation with ground fill.

Verify that there are plenty of ground vias in the shield attachment area. Also verify that
there are no non-ground vias in the shield attachment area. Avoid traces crossing into the
shield area on the shield layer.
3. Consider the following RF design practices:

Confirm antenna ground keep-outs.

Verify that the RF path is short, smooth, and neat. Use curved traces or microwave
corners for all turns; never use 90-degree turns. Avoid width discontinuities over pads. If
trace widths differ significantly from component pad widths, then the width change should
be mitered. Verify there are no stubs.

Do not use thermals on RF traces because of their high loss.
4
The information contained herein is the exclusive property of AzureWave and shall not be distributed, reproduced, or disclosed
in whole or in part without prior written permission of AzureWave.

The RF traces between AW-NM288SM WL_BT_ANT pin and antenna must be made
using 50Ω controlled-impedance transmission line.
5
The information contained herein is the exclusive property of AzureWave and shall not be distributed, reproduced, or disclosed
in whole or in part without prior written permission of AzureWave.
2. Ground Layout
Please follow general ground layout guidelines. Here are some general rules for customers’
reference.

The layer 2 of PCB should be a complete ground plane. The rule has to be obeyed strictly
in the RF section while RF traces are on the top layer.

Each ground pad of components on top layer should have via drilled to PCB layer 2 and
via should be as close to pad as possible. A bulk decoupling capacitor needs two or more.

Don’t place ground plane and route signal trace below printed antenna or chip antenna to
avoid destroying its electromagnetic field, and there is no organic coating on printed
antenna. Check antenna chip vendor for the layout guideline and clearance.

Move GND vias close to the pads.
3. Power Layout
Please follow general power layout guidelines. Here are some general rules for customers’
reference.

A 4.7uF capacitor is used to decouple high frequency noise at digital and RF power
terminals. This capacitor should be placed as close to power terminals as possible.

In order to reduce PCB’s parasitic effects, placing more via on ground plane is better.
4. Digital Interface
Please follow power and ground layout guidelines. Here are some general rules for customers’
reference.

The digital interface to the module must be routed using good engineering practices to
minimize coupling to power planes and other digital signals.

The digital interface must be isolated from RF trace.
5. RF Trace
The RF trace is the critical to route. Here are some general rules for customers’ reference.

The RF trace impedance should be 50Ω between ANT port and antenna matching network.
6
The information contained herein is the exclusive property of AzureWave and shall not be distributed, reproduced, or disclosed
in whole or in part without prior written permission of AzureWave.

The length of the RF trace should be minimized.

To reduce the signal loss, RF trace should laid on the top of PCB and avoid any via on it.

The CPW (coplanar waveguide) design and the microstrip line are both recommended;
the customers can choose either one depending on the PCB stack of their products.

The RF trace must be isolated with aground beneath it. Other signal traces should be
isolated from the RF trace either by ground plane or ground vias to avoid coupling.

To minimize the parasitic capacitance related to the corner of the RF trace, the right angle
corner is not recommended.
If the customers have any problem in calculation of trace impedance, please contact AzureWave.
Correct RF trace
Right-angled corner
Via on RF trace
Incorrect RF trace
7
The information contained herein is the exclusive property of AzureWave and shall not be distributed, reproduced, or disclosed
in whole or in part without prior written permission of AzureWave.
6. Antenna
All the high-speed traces should be moved far away from the antenna. For the best radiation
performance, check antenna chip vendor for the layout guideline and clearance.
7. Antenna Matching
PCB designer should reserve an antenna matching network for post tuning to ensure the antenna
performance in different environments. Matching components should be close to each other. Stubs
should also be avoided to reduce parasitic while no shunt component is necessary after tuning.
8
The information contained herein is the exclusive property of AzureWave and shall not be distributed, reproduced, or disclosed
in whole or in part without prior written permission of AzureWave.
8. SHIELDING CASE
Magnetic shielding, ferrite drum shielding, or magnetic-resin coated shielding is
highly recommended to prevent EMI issues.
9. GENERAL LAYOUT GUIDELINES
Follow these guidelines to obtain good signal integrity and avoid EMI:
1. Place components and route signals using the following design practices:

Keep analog and digital circuits in separate areas.

Identify all high-bandwidth signals and their return paths. Treat all critical signals as
current loops. Check each critical loop area before the board is built. A small loop area is
more important than short trace lengths.

Orient adjacent-layer traces so that they are perpendicular to one another to reduce
crosstalk.

Keep critical traces on internal layers, where possible, to reduce emissions and improve
immunity to external noise.

However, RF traces should be routed on outside layers to avoid the use of vias on these
traces.

Keep all trace lengths to a practical minimum. Keep traces, especially RF traces, straight
wherever possible. Where turns are necessary, use curved traces or two 45-degree turns.
Never use 90-degree turns.
2. Consider the following with respect to ground and power supply planes:

Route all supply voltages to minimize capacitive coupling to other supplies. Capacitive
coupling can occur if supply traces on adjacent layers overlap. Supplies should be
separated from each other in the stack-up by a ground plane, or they should be coplanar
(routed on different areas of the same layer).

Provide an effective ground plane. Keep ground impedance as low as possible. Provide
as much ground plane as possible and avoid discontinuities. Use as many ground vias as
possible to connect all ground layers together.
9
The information contained herein is the exclusive property of AzureWave and shall not be distributed, reproduced, or disclosed
in whole or in part without prior written permission of AzureWave.

Maximize the width of power traces. Verify that they are wide enough to support target
currents, and that they can do so with margin. Verify that there are enough vias if the
traces need to change layers.
3. Consider these power supply decoupling practices:

Place decoupling capacitors near target power pins. If possible, keep them on the same
side as the IC they decouple to avoid vias that add inductance. If a filter component cannot
be directly connected to a given power pin with a very short and fat etch, do not connect
it by a copper trace. Instead, make the connection directly to the associated planes using
vias.

Use appropriate capacitance values for the target circuit, and consider each capacitor's
self- resonant frequency.
10. Stamp Module stencil and Pad opening Suggestion
Stencil thickness：0.10~0.12mm
Function Pad opening size suggestion: Max. 1:1
PS: This opening suggestion just for customer reference, please discuss with
AzureWave’s Engineer before you start SMT.
Example:
10
The information contained herein is the exclusive property of AzureWave and shall not be distributed, reproduced, or disclosed
in whole or in part without prior written permission of AzureWave.
11
The information contained herein is the exclusive property of AzureWave and shall not be distributed, reproduced, or disclosed
in whole or in part without prior written permission of AzureWave.
11. The other layout guide Information

Make sure every power traces have good return path (ground path).

Connect the input pins of unused internal regulators to ground.

Leave the output pins of unused internal regulators floating.

High speed interface (i.e. UART/SDIO/HSIC) shall have equal electrical length. Keep
them away from noise sensitive blocks.

Good power integrity of VDDIO will improve the signal integrity of digital interfaces.

Good return path and well shielded signal can reduce crosstalk, EMI emission and
improve signal integrity.

RF IO is around 50 ohms, reserve Pi or T matching network to have better signal transition
from port to port.

Smooth RF trace help to reduce insertion loss. Do not use 90 degrees turn (use two 45
degrees turns or one miter bend instead).

Well-arranged ground plane near antenna and antenna itself will help to reduce near field
coupling between other RF sources (e.g. GSM/CDMA … antennas).

Discuss with AzureWave Engineer after you finish schematic and layout job.
12
The information contained herein is the exclusive property of AzureWave and shall not be distributed, reproduced, or disclosed
in whole or in part without prior written permission of AzureWave.
12. Mechanical Drawing
• Package Outline Drawing
13
The information contained herein is the exclusive property of AzureWave and shall not be distributed, reproduced, or disclosed
in whole or in part without prior written permission of AzureWave.
•Top View of PCB Layout Foot Print
14
The information contained herein is the exclusive property of AzureWave and shall not be distributed, reproduced, or disclosed
in whole or in part without prior written permission of AzureWave.