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LARA-R2 series - System Integration Manual

UBX-16010573 - R02

Objective Specification

Design-in

Page 121 of 148

2.12

Thermal guidelines

Modules’ operating temperature range is specified in

LARA-R2 series

Data Sheet

[1].

The most critical condition concerning module thermal performance is the uplink transmission at maximum
power (data upload in connected-mode), when the baseband processor runs at full speed, radio circuits are all
active and the RF power amplifier is driven to higher output RF power. This scenario is not often encountered in
real networks (for example, see the Terminal Tx Power distribution for WCDMA, taken from operation on a live
network, described in the

GSMA TS.09 Battery Life Measurement and Current Consumption Technique

[16]);

however the application should be correctly designed to cope with it.
During  transmission  at  maximum  RF  power  the  LARA-R2  series  modules  generate  thermal  power  that  may
exceed 2 W: this is an indicative value since the exact generated power strictly depends on operating condition
such as the actual antenna return loss, the number of allocated TX resource blocks, the transmitting frequency
band,  etc.  The  generated  thermal  power  must  be  adequately  dissipated  through  the  thermal  and  mechanical
design of the application.
The  spreading  of  the  Module-to-Ambient  thermal  resistance  (R

th,M-A

) depends on the module operating

condition. The overall temperature distribution is influenced by the configuration of the active components
during the specific mode of operation and their different thermal resistance toward the case interface.

The Module-to-Ambient thermal resistance value and the relative increase of module temperature will
differ according to the specific mechanical deployments of the module, e.g. application PCB with different
dimensions and characteristics, mechanical shells enclosure, or forced air flow.

The increase of the thermal dissipation, i.e. the reduction of the Module-to-Ambient thermal resistance, will
decrease the temperature of the modules’ internal circuitry for a given operating ambient temperature. This
improves the device long-term reliability in particular for applications operating at high ambient temperature.
Recommended hardware techniques to be used to improve heat dissipation in the application:



Connect each

GND

pin with solid ground layer of the application board and connect each ground area of

the multilayer application board with complete thermal via stacked down to main ground layer.



Provide a ground plane as wide as possible on the application board.



Optimize antenna return loss, to optimize overall electrical performance of the module including a decrease
of module thermal power.



Optimize the thermal design of any high-power components included in the application, such as linear
regulators and amplifiers, to optimize overall temperature distribution in the application device.



Select the material, the thickness and the surface of the box (i.e. the mechanical enclosure) of the
application device that integrates the module so that it provides good thermal dissipation.

Further hardware techniques that may be considered to improve the heat dissipation in the application:



Force ventilation air-flow within mechanical enclosure.



Provide a heat sink component attached to the module top side, with electrically insulated / high thermal
conductivity adhesive, or on the backside of the application board, below the cellular module, as a large part
of the heat is transported through the GND pads of the LARA-R2 series LGA modules and dissipated over
the backside of the application board.

For example, the Module-to-Ambient thermal resistance (R

th,M-A

) is strongly reduced with forced air ventilation

and a heat-sink installed on the back of the application board, decreasing the module temperature variation.
Beside the reduction of the Module-to-Ambient thermal resistance implemented by proper application hardware
design, the increase of module temperature can be moderated by proper application software implementation:



Enable power saving configuration using the AT+UPSV command (see section 1.14.16).



Enable module connected-mode for a given time period and then disable it for a time period enough long to
properly mitigate temperature increase.