coupling effects during thermo- fluidic analysis of flip ... nowak.pdf · t. nowak imaps thermal...

T. NowakIMAPS Thermal Management2017 La Rochelle

11

Coupling Effects during Thermo-Fluidic Analysis of Flip-Chip

Devices with Peripheral Components – CFD Simulation

and Experimental Study

- Torsten Nowak -

17/02/02 IMAPS Thermal Management La Rochelle

[email protected]


CONTENT

1. BTU?2. Motivation for the topic3. Parametric studies4. Experimental setup5. CFD modeling6. Validation results7. Summary and outlook

2


Foundation: 1st July 2013 Brandenburgische Technische Universität (BTU) Cottbus-Senftenberg 8.200 students for research and near to technical applications About 21 % of the students came from more than 100 different countries

208 Professors and Junior-Professors 645 Academic Employees

BTU = Awesome buildings + state-of-the-art equipment + modern learning methods

3

FACTS AND FIGURES

Library, Campus Cottbus

Percentage of international students


4

INTERNATIONAL CORRELATIONS

The BTU actually cooperates with more than 235 partners in 49 countries.


Department Electronic Circuit TechnologiesProf. Dr.-Ing. Ralph Schacht

Department Aerodynamics and Fluid MechanicsProf. Dr.-Ing. Christoph Egbers

5

FACULTIES

FACTS AND FIGURES


Motivation

6

Source: ansys.com

Vorführender

Präsentationsnotizen

The idea behind…


Motivation

Aim of this essential study are the knowledge of thermal impacts and action-related dependencies of Thermal conductivity of a Printed Circuit Board (PCB) coupled by Thermo-fluidic convection via fluid flow

Parametric analysis of thermal coupling effects in dependency of: Distances between components (d): 8 or 16 mm Different fluid flow velocimetry (v): 0 … 5 m/s Power losses of active thermal test dies (Pv): 0 … 4 W Different obstacles between active components Thermal conductivity of the PCB (λ): 4L or 2L Multiple test boards for rack system analysis (xn) 7

Possible obstacles

Tem

pera

ture

-di

strib

utio

n?

Fluid measurement and visualization??


Design and possibilities of the test PCB

8

3 Thermal Test Chips (TTC), assembled in Flip-Chip (FC) technology 5 NTC‘s in SMD technology for board level temperature monitoring

NTC 1

Card edge connector forTTC T-measurement

Card edge connector for TTC heating and NTC T-measurement

T-Sensor position

16 mm

16 mmd

TTC 1 TTC 2 TTC 3Fluid flowdirection

NTC 2

NTC 3NTC 4NTC 5

130 mm80

mm

24 mmHeating

areaHeating

area

Solderpads

Tsens

3,2 mm

3,2 mm

Hea

ter-

strin

gs

1x TTC cell

Possible position foran fluid flow obstacle

Vorführender


Making first steps


Schematic sketch of the test assembly in wind tunnel measurement section

The TTC data measurement and heating control will be realized by in-situ monitoring by LabVIEW with external trigger box

9

(cross section) (top view)


Experimental setup in wind tunnel

CONNECT, Stokes Laboratories, University of Limerick, Limerick, Ireland

10

IR-Cam

Measurement section DiffusorContraction

DAQ / Electronic

Fan speed control

IR Cam control

Sensor / heat control

Air inlet

Ventilator

4 m

1 m

0,6

m

0,3

m


Experimental setup in wind tunnel- Measurement section -

11

Test board

PCB holder

View through honeycomb filter inlet

IR-Cam

PCB test board

PCB holder

IR transparent window

Measurement section of the wind tunnel system

IR measurement with adopted emissivity (black varnish, ε = 0.92) on PCB test surface (capacitor as

an obstacle instead of TTC2)

PCB holding system with card edge connectors (capacitor as an obstacle instead of TTC2)


Particle Image Velocimetry / PIV

12

Measurement of particle motion, not fluid motion!

Source: http://www2.cscamm.umd.edu/programs/trb10/presentations/PIV.pdf


Particle Image Velocimetry / PIV- Setup and first results -

Measurement and resolution of fluid flow near thermal boundary layer of TTC2

13

PIV flow visualization

BubbleLeading edge

Leading edgeTTC 1 TTC 2

PIV vector plot

Laser sheet(low fire)

TTC 1TTC 3

Lens

Lens

Camera

Laser

Thermal boundary layer(laminar flow)

PCB

5 m/s


MODELING

14


CFD modelingMeasurement section, dimensions, boundary conditions

15

Name value

Ambient temperature (wind tunnel walls) 298 K

Outlet pressure 0 Pa

Inlet velocity (T = 298 K)0 … 5 m/s

Distance between TTC’s 8, 16 mm

Distance from PCB-edge to TTC1 24 mm

Name x [ mm ]

y[ mm ]

z [ mm ]

FR4 90 130 1.6

TTC 16 16 0.670

PV Volume TTC 16 16 0.1Solder bump (Cu + SnAg) 0.1 0.1 0.75+0.25

UF / Solder bump volume 16 16 0.1

Wind tunnel / measurement section

300 1000 300

PCB holder 105 140 20

Fluid flow help 105 35 (center) 20 0

300

mm

Outlet

Inlet

Wallp = 0 Pa T = 298 K (const.)

v = 0…4 m/s


CFD modelingPCB dimensions, material data

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PCB card holder and PCB dimensionsMaterial Thermal Conductivity [W/mK]

FR4-4L Cu (x / y / z) 17.4 / 17.4/ 0.314

FR4-2L Cu (x / y / z) 0.8 / 0.8 / 0.3

Air (25 ˚C) 0.0261

FR4 (x / y / z) 0.8 / 0.8 / 0.4

Under fill (UF) 0.63

SnAg 52

Cu (galv.) 300

Cu 380

Si 150

UF_SodlerBump,eff 3.82

PCB holder 0.27

PCB cardcarrier (acryl glass)

PCB

20 mm

cap


CFD modelingPCB solder bumps and under fill

PCB-, TTC- dimensions as cross section Power loss will be generated in thin silicon die (active area to bottom)

in a separate volume The ‘solder bump / under fill’ volume will be modeled as thin layer (100 µm)

17

1.6 mm

0.57 mm0.1 mm

Chip (Si)

PCB (FR-4)

Contact as ‚thin layer‘ modeled (100 µm),Instead of under fill layer with tiny solder balls (30 µm)

Power loss in this thin Si volume (16 x 16 x 0.1 mm³)


CFD modelingMesh setup and boundary conditions

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The fluid properties were set to: Morphology ‘Continuous Fluid’ for ‘Air at 25 °C’

Heat transfer ‘Thermal Energy’ incl. ‘Viscous Dissipation’

Turbulence option ‘Shear Stress Transport’, ‘Automatic’ wall func.

Mesh: A total number of 9,329,078 elements (Tetrahedral for the wind tunnel, Wedges and Hexahedral for PCB, -holder) as 2,451,995 nodes were required.


CFD results- Flow contour plot / distribution in wind tunnel -

Flow velocity distribution of wind tunnel: air direction flow from left to right

19


CFD results, examplePCB test design 4L8-A/B

20

With

out o

bsta

cle

Cap

acito

r 2C

apac

itor 3

PD,TTC1 = 2.5 W, v = 1.43 m/s

Temperature [K]Velocity [m/s]

h = 11 mmd = 8 mm

h = 15 mmd = 13 mm

h = 11 mmd = 8 mm

h = 15 mmd = 13 mm

TTC2 TTC2


Simulation resultsExample with capacitor

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Capacitordimensions

Height[mm]

Diameter[mm]

2 11 83 15 13

PCB testdesign 4L8

0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.50

5

10

15

20

25Pv,TTC1 = 2.5 W w/o cap

cap2 cap3

∆TTT

C [K]

v [m/s]

0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.570

75

80

85

90

95

100

~10

%

Pv,TTC1 = 2.5 W

cap2 cap3

T cap/T

w/o_

cap [

%]

v [m/s]

Vorführender


The increase of obstacle size have an influence by temperature reduction of nearby TTC’s. Convective heat transfer by fluid flow (air) is reduced. Only conductive heat transfer along the PCB board have temperature influences from TTC1 to TTC3. The cap-size influences the heat transfer by 10 %.


Comparison between simulation and experiment

Example with capacitor: The increase of obstacle size have an influence by temperature reduction of nearby TTC’s. Convective heat transfer by fluid flow (air) is reduced. Only conductive heat transfer along the PCB board have temperature influences from TTC1 to TTC3.

22

PCB test design 4L8-B

1 2 3 40

1020304050607080

v = 1 m/s TTC1-Sim TTC1-Exp TTC3-Sim TTC3-Exp

∆TTT

C [K]

PV,TTC1 [W]


Summary / Outlook

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Development of analytical model equations for thermo-fluidic coupling effects with consideration of interferences of peripheral components between in FC technology assembled unhoused bare dies

Validation of experimental and numerical data for calculation of thermo-fluidic factor


Thank youfor your attention!

[email protected]


07Aero Dynamics and Fluid Mechanics in Cottbus

Laboratories Aero- and Fluid Dynamics


Faculty 3 – Chair of aerodynamic and fluid mechanics campus Cottbus

Wind tunnel ‘Göttinger’ setup:- Section of measurement

A = 0,6 m x 0,5 m (rectangle)- closed / open for PIV/LDA- Velocimetry Umax.= 50 m/s

(closed measurement section)- Rated speed

Urs. = 40 m/s ± 0,1 m/s- Intensity of turbulence: Tu < 0,1 %

26Address for VisitorsBuilding 3ASiemens-Halske-Ring 1403046 Cottbus / Germany

LabLaboratories 3DSiemens-Halske-Ring 1503046 Cottbus / Germany

https://www.b-tu.de/fg-aerodynamik-stroemungslehre/forschung/ausstattung/windkanal

For fluid visualization and measurement methods (e.g. LDA, PIV) a three way opticalaccess for the measurement section will be necessary.

Prof. Dr.-Ing. Christoph Egbers

coupling effects during thermo- fluidic analysis of flip ... nowak.pdf · t. nowak imaps thermal...

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