electronics cooling applications with ansys icepak 12.0

© 2009 ANSYS, Inc. All rights reserved. 1 ANSYS, Inc. Proprietary© 2009 ANSYS, Inc. All rights reserved. 1 ANSYS, Inc. Proprietary

Electronics cooling applications with ANSYS Icepak 12.0

Electronics cooling applications with ANSYS Icepak 12.0

Fadi Ben AchourANSYS Inc.Fadi Ben AchourANSYS Inc.

© 2009 ANSYS, Inc. All rights reserved. 2 ANSYS, Inc. Proprietary

Contents

• SIwave-ANSYS Icepak Coupling – SIwave and ANSYS Icepak

Overview– One-way Load Transfer– Advantages and Limitations– Joule Heating and Conductivity

Sensitivity examples• Fan modeling

– Moving reference frame (MRF)– Using multilevel meshing form HDM mesher


SIwave

• What is SIwave?– Hybrid 2.5D full wave EM

field solver– Models layered structures– Analyses performed

• Signal Integrity• Power Integrity• Electromagnetic

Compatibility/Interference


SIwave: DC IR Solution

Voltage Loss Distribution Current Density Distribution

I2R Distributed heat source

Add Sources and Sinks for easy analysis

Links to ANSYS Icepak


ANSYS Icepak

ANSYS Icepak is robust and powerful computational fluid dynamics (CFD) software for electronics thermal management of packages, boards and systems.

• Steady State and Transient– Conjugate Heat Transfer– Conduction– Convection– Radiation

• Package, Board, and System Level Analysis


Flexible Automatic Meshing

• Highly Accurate Conformal Meshing– Represents the true shape of electronic components– Accurately resolves fluid boundary layer– Hexahedral, tetrahedral and hex-dominant options

Multi-level hex-dominant mesh on a heat sink-fan assembly

Pin fin heat sink, mesh follows the geometry without any approximation.


• Working to Integrate Tools– Initial one-way data exchange of DC power distribution– Available in SIwave 4.0 and ANSYS Icepak 12.0– Applicable for package and PCB thermal distribution

Integration of Tools

Current Density Power Distribution Temperatures


Coupling Advantages

• Straight forward, easy to understand and use• Independent SIwave and ANSYS Icepak

meshes• Independent SIwave and ANSYS Icepak

solution sequences and post-processing• All ANSYS Icepak thermal-flow capabilities

are supported• Accuracy control of load mapping

– Min thermal cell size– Min power loss per cell


Joule Heating ExampleDemonstrate the benefits of tools Integration

• Help PCB designers make more informed decisions on:– Power dissipation – Current constraints– Thermal issues

• General Procedure1. Run “DC IR Drop” analysis in

SIwave2. Transfer Joule heating data

from SIwave to ANSYS Icepak3. Run thermal simulation with

ANSYS Icepak

SIwave (Trace Layers) 2.5 D Model

Icepak (Tracer Layers and Components) 3D Model


SIwave Modeling Details

Single Via from VRM on top layer down to supply plane, VCC

Package Sink Locations


• Export Power Dissipation to ANSYS Icepak– Min Thermal Cell Size: 3 mm– Min Power Loss Per Cell: 0.05 milliwatts

Export Power Dissipation

Output files (.OUT) that ANSYS Icepak reads will be located in the project directory.


Import Joule Heat Distribution

2 mm & 0.1mW (More Detail)

10 mm & 50 mW (Less Detail)

Specify .out files from SIwave for each layer.


Results: Current Density from SIwave & ANSYS Icepak Temperature Contours

ANSYS Icepak :Temperature Contours

SIwave :Current Density

Joule Heating (included)


Results: Max Temperature on Components

71%

21%

Tem

pera

ture

(C )

U1 U2

U6

U5

U7

U13U9 U10

Temperature (C) Temperature (C)

PCB 70 120

U1 63 64

U10 40 42

U11 52 52

U12 57 55

U13 31 33

U14 59 63

U2 70 85U3 43 44U4 68 67U5 32 32U6 31 31U7 53 57U8 47 50U9 38 40

With Joule heatWithout Joule heat


• Increased temperature leads to reduction in electric conductivity or increase electric resistance

• Increased in electric resistance leads to higher joule heating loses• Increase in joule heating leads to a second order increase in

temperature and electric resistance

Electrical Conductivity Of Copper : s1 = s2 / [1 + a * (T1–T2)] , a= 0.0040 /C

Sensitivity Analysis on Electric Conductivity

Temperature (C) Conductivity (S/m)

Case#1 25 5.81E+07

Case#2 50 5.28E+07

Case#3 75 4.80E+07

Case#4 100 4.37E+07

http://www.ndt-ed.org/EducationResources/CommunityCollege/Materials/Physical_Chemical/Electrical.htmReference:

Where: s1 = conductivity value adjusted to T1s2 = conductivity value known or

measured at temperature T2a = Temperature CoefficientT1 = Temperature at which conductivity

value needs to be knownT2 = Temperature at which known or

measured value was obtained


Results: Voltage DropComparison Between Case #1 and #4

Case#1 Case#41.8v

1.77v

1.8v

1.77v


Results: Temperature Contours Comparison Between Case #1 and #4

Case#1 Case#4


Results: Max. Temperature and Total Power on the PCB

Case#1 Case#2 Case#3 Case#4

PCB 40.73 42.78 45.17 47.32

Component Name

Tem

pera

ture

(C )Temperature (C)

Tota

l Pow

er (

W)

Component Name

Case#1 Case#2 Case#3 Case#4

PCB 0.8079 0.887 0.976 1.072

Total Power (W)


Conclusions

• Initial integration work of ANSYS and Ansoft products is underway

• Easy, straight foreword methodology for electromagnetic thermal coupling

• Independent SIwave and ANSYS Icepak models

• Similar analysis environments• Creates the foundation for future

multiphysics coupling!– Transfer temperature profile back to SIwave


Need for advanced Fan Modeling with MRF: (Moving Reference Frame)

• Fan object allows for only simplified modeling of fan behavior – Pressure drop versus flow rate (P-Q) curve can be system dependent– Cannot model flow reversal in some regions on the fan surface– Does not incorporate the effects of blade geometry– Difficult to quantify the input for swirl?

• Moving reference frame model provides more accurate representation of the fan flow characteristics


Advanced Fan Modeling:Need for MRF – Swirl

MRF Fan

Fan Object

Wind tunnel comparison• Swirl – radial & tangential

flow components are better captured in MRF fan

• If swirl is not captured:– Flow penetration is

exaggerated - usually the case with fan object

– Fan object may show excessive cooling i.e.; lower temperatures


Advanced Fan Modeling:Creating MRF Fan/Impeller

1. Create fan/impeller model– Axial fan Model blades & hub as ANSYS Icepak CAD block – Impeller Model blades & hub as ANSYS Icepak polygon blocks/ CAD block – ANSYS Icepro recommended

2. Create cylindrical fluid block covering entire rotor (blade + hub)3. Ensure higher mesh priority to the rotor geometry inside the fluid block4. Create accurate body-fitting mesh using Multi-level Mesher-HD


Meshing fan geometry with Multi-Level Meshing

No Multi-level MeshMesh size = 0.4 mm; Count = 931k

Multi-level MeshMesh size = 2 mm; Count = 343k


Advanced Fan Modeling:Areas of Application

• Ideal MRF fan applications → where flow resistances are close to the fan– Active heat sinks– Telecom rack like system with cards near fan tray– “High density boxes” like power supply units

• Vendor’s fan curve may not be applicable in these cases – MRF fan does not rely on fan curve

• Fan object may not capture effect of radial and tangential flow components


Advanced Fan Modeling:Case Study 1: Fan Selection

Fan object : 1.41MType A (MRF): 1.55MType B (MRF): 1.44M

Which fan provides better cooling to the projector bulb: Type A or Type B ?

Type A Type B


TypeA TypeB Fan object

Advanced Fan Modeling:Case Study 1: Results


Advanced Fan Modeling:Case Study 2: PSU

Fan object

Fan object

MRF

MRF


Advanced Fan Modeling:Case Study 3: Telecom Rack

Failed Fan-Back flow into failed fan from adjacent fans-Recirculation of heated air


Conclusion

• SIwave-ANSYS Icepak Coupling – Enables more accurate simulation of joule heating in

PCB and package traces– Allows a more comprehensive and integrated

multiphysics design that reduces failures due to over heating and thermal-stress

– Users has options to incorporate second order effects of dependence of copper properties on temperature

• MRF fan modeling – MRF modeling enables more accurate predictions of flow

patterns and system pressure drop in high density electronics – MRF reduces error in predicting component temperatures– MRF provides additional accuracy in predicting flow

turbulence and system noise levels

electronics cooling applications with ansys icepak 12.0

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