Case study

Better electronic enclosuresby CFD simulation
SIENNA ECAD leverage Cradle CFD with conjugate heat transfer toenhance the cooling performance of a 12mm thick enclosure for a
PCB using Cavity and TIM design

SIENNA ECAD is one of India’s leading PCB design andanalysis engineering companies located in Bangalore,
India, with over 25 years of experience in the evolutionof the global electronics industry. They specialisein engineering services designing complex PCB
layouts, simulation and analysis of designs, librarymanagement, DFX and prototyping, and more to aid
their customers in segments including networking,power, transportation, semiconductor, IoT, andmedicine.
PCB Engineering team works with clients across theglobe, finding solutions for highly complex PCB design
problems meeting IPC specifications. Their PCB
Engineering solutions include High-Speed PCB Design,
SI Analysis (Time Domain and Frequency Domainanalysis), Power Integrity analysis, Thermal EMI/EMC
and Reliability Analysis.
The parent companies Sienna Corporation and Avalon
Technologies are Electronics Manufacturing Services
providers based in the USA and India with facilities inAtlanta, Fremont, Chennai, and Bangalore.

Cradle CFD enabled us to
get actionable insightsof the thermal flow inor design and quickly
identify the design flaws
that ensured that wecould innovate the designand create an enclosurethat helped address ourtemperature requirements
and size constraints.”
Suresh Nidasesi,
Project Manager (Design and Analysis),
SIENNA ECAD

scSTREAM drive better thermal design
One particular challenging PCB design project for thePCB Engineering team was incorporating two System
on Modules, SoM, each with over 1000 components
inside an IP64 compliant, dust-tight and no effect ofsplashing water, enclosure only 12mm thick. Further,
the team needed to find a design where the total power
dissipation of the system was below 250W, and it wasrequired to operate around the clock all year round in aharsh environment at an elevated temperature, exposed
to direct sunlight. Simply put, conditions made to makeelectronics fail.
The design space provided also created challenges as
the design needed to fit in a small space in an existing
enclosure; hence it was initially decided to evaluate themulti-board design with a custom heat sink that reliedon natural convection for cooling without fans or othercooling devices.
Initial design analysis by scSTREAM, a part of Cradle
CFD, showed that the temperature in the first design
reached as high as 250-280°C, while the maximum
temperature design target was set to 125°C for normal or
85-90°C for RF & high-speed components.
The CFD analysis contained the mechanical CAD
model of the enclosure and the ECAD of the two SoM
considered radiation and conjugated heat transfer,e.g. considering heat transfer of both fluids and solids.
The PCB had anisotropic material parameters to model
difference heat transfer in-plane and normal directions.

2Manufacturing Intelligence hexagonmi.com

Bottom heat sink

Top heat sink

The analysis demonstrated that the existingarrangement of the heat sink enclosure was inadequate
to manage the temperature. The team explored options
such as changing the heat sink parameters such as fin
sizes or length; however, this did not prove helpful in
reducing the temperature. Thus, innovative methods toovercome the challenge was needed.

contact with it as they were recessed in the PCB, thus
directly being exposed to it acting as a heat sink. TIM(PCM780SP) was further used to enhance heat transfer.
The team quickly adopted the scSTREAM model to thenew design changes, and simulation promptly showedthat the temperatures of the PCBs and the enclosure
were well was within the design target.

The team decided to explore the option of using a
Thermal Interface Material (TIM) and cavity design,where components are placed in cutouts, consequently
not connecting to the top or bottom PCB layer. In thisapproach, the enclosure design had each component

The CFD simulation helped the PCB Team meet thedesign target and the design phase rule out the initialdesign to reduce design interaction and avoid expensive
prototype testing with the help of thermal simulation
solutions provided by Hexagon.

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