Thermal Management for Electronic Packaging

Transcription

1 Thermal Management for Electronic Packaging 03/02/2006 Guoping Xu Sun Microsystems

2 Outline CSE291: Interconnect and Packaging, UCSD, Winter 2006 Introduction Heat transfer theory Thermal resistance in electronic packaging Thermal design Thermal modeling Thermal measurement Page 2

3 Introduction Functions of Electronic Packaging Package protection Signal distribution Power distribution Heat dissipation Page 3

4 Introduction Packaging Hierarchy Chip Package Board System Rack Room Page 4

5 Introduction High end chip power trend 600 CPU Power, (W) UltraSparc [1] Power 4 [2] Itanium 2 [3] ITRS 2002 [4] ITRS Year Page 5

6 Introduction Cost performance chip power trend ITRS CPU Power, (W) Year Page 6

7 Introduction Power density in datacom equipment Page 7

8 Introduction Power density in datacom equipment Total power: 24KW Footprint: 15 sq. ft Power density: 1600W/sq. ft Sun Fire E25K Page 8

9 Introduction Impact of Device junction temperature Computing performance Reliability Fire hazard and/or Safety issues Page 9

10 Heat Transfer Theory Conduction Definition: Conduction is a mode of heat transfer in which heat flows from a region of higher temperaure to one of lower temperature within a medium (solid, liquid, or gases) or media in direct physical contact Fourier's law: Q = -KA(dT/dX) 1-D conduction: Q = -KA (T1-T2)/L Thermal resistance: R = (T1-T2)/Q = L/(KA) Page 10

11 Heat Transfer Theory Conduction Contact thermal resistance Page 11

12 Heat Transfer Theory Thermal conductivity of various packaging materials Material W/mK Aluminum (pure) 216 Aluminum Nitride 230 Alumina 25 Copper 398 Diamond 2300 Epoxy (No fill) 0.2 Epoxy (High fill) 2.1 Epoxy glass 0.3 Gold 296 Lead 32.5 Silicon 144 Silicon Carbide 270 Silicon Grease 0.2 Solder 49.3 Page 12

13 Heat Transfer Theory Convection Convection: is a mode of heat transport from a solid surface to a fluid and occurs due to the bulk motion of the fluid. Newton's law: Q= ha (Tw- Tf) Convective thermal resistance: R= 1/(hA) Effects of heat transfer coefficient Convetion mode: Natural convection, Foreced convection, phase change Flow regime: Laminar, Turbulent flow y Fluid y Flow velocity Surface condition Fluid Velocity distribution u(y) Heated surface T f Temperature distribution T w T(y) Page 13

14 Heat Transfer Theory Typical values of the heat transfer coefficient Page 14

15 Heat Transfer Theory Radiation Definition: Radiation heat transfer occurs as a result of radiant energy emitted from a body by virtue of its temperature. Page 15

16 Thermal Resistance -Package without heat sink Tb Ta Chip Tt Tj Package PCB Rja: Junction to air thermal resistance Rja= (Tj-Ta)/P Low value is good thermal perfromance Rjc: Junction to case thermal resistance Rjc = (Tj-Tc)/P Ψjt: Thermal characterization parameter: Junction to package top, NOT thermal resistance. Ψjb: Thermal characterization parameter: Junction to board Page 16

17 Thermal Resistance -Package with heat sink Ta Heat sink Package Die Ts Tc Tj Rja: Junction to air thermal resistance Rja= (Tj-Ta)/P=Rjc +Rcs+Rsa Rjc: Junction to case thermal resistance Rjc = (Tj-Tc)/P Rsa: External heat sink thermal resistance Rsa= (Ts-Ta)/P Page 17

18 Thermal Resistance -PBGA package example Tair Page 18

19 Thermal Resistance -Impact factors for package without heat sink Die size Package size, lead count Packaging material thermal condunctivity Material thickness in major heat flow path Number of vias Heat spreader or heat slug Air velocity and temperature PC Board size Board configuration and material Board layout Page 19

20 Thermal Design Conduction application Single material Composite material Q Die Substrate Tc Tj t i K in-plane Layer 1 Layer 2 Layer i Layer N Tc = Tj - QL/(KA) K Tthrough Uniform heating on the die Page 20

21 Thermal Design Conduction application Heat spreader Die Substrate R sb k A b 2 b A 3 b A A 1 A b A s s s kb A 1 k b b R A ba b ba tanh H R tanh H b b A b : Heat spreader base area A s : Heat source area H b : Heat spreader thickness K b : Heat spreader thermal conductivity Page 21

22 Thermal Design Convection application-heat sink design H f H b t f Fins H b Heat sink base L W Page 22

23 Thermal Design Convection application-heat sink design Thermal resistance: Heat transfer: Nu R hd k h air ba T b T Q inlet. mc p (1 e 1 ha 7.54 Laminar flow t o. mc p ) Nu hd k h air 0.024Re Pr 0.45 Turbulent flow Fin efficiency: Af o 1 1 A t f f tanh(mh ) mh f f Page 23

24 Thermal Design Convection application-heat sink design Total static pressure loss: P Kc 4 f Apparent friction factor f app calculation Fully developed flow friction factor f f app L D h K e 2 ch U 2 Culham and Muzychka (2001) David Copeland (2000) Re * Re * 0.57 f app L f Re Re 3.2L f Re b H f b H f b H f f Re b H f b H f b H 1 2 f 6.089b H 5 f Contraction loss coefficient K c K c K c Expansion loss coefficient K e K 1 2 K e f app e * L D h L Re Nt 1 W f t f b b Page 24

25 Thermal Design Convection application- Heat sink design Impact factors Air flow rate Available space Heat sink base and fin material Fin pitch and fin thickness Heat flux Heat sink technologies Page 25

26 Thermal Design Design methodology Define requirements Analyze given package design Identify major heat paths and paths for improvements Consider and assess potential improvements Detail analysis/modeling Build prototypes Thermal testing Page 26

27 Modeling Finite Element Method (FEM) Software: ANSYS Solve conduction problem within package or board Require input data: material propoerties, package/board construction/geometry Boundary conditions: Heat source distribution on the die or board Effective convective heat transfer coefficient on the surface of the package or board Page 27

28 Modeling Finite Element Method Procedure: Create package/board geometry or import from CAD file Mesh Input material properties and assign boundary conditions Solve Post-process Page 28

29 Modeling Finite Difference Method (FDM ) Computational Fluid Dynamics (CFD) Commercial software: Flotherm, Fluent Solve the temperature field and flow field Not only solve the conduction, also on convection, radiation and phase change Required input: Geometry, flow conditions, material properties including fluid Mesh dependent on the chosed model Page 29

30 Modeling Finite Difference Method (FDM ) Example Page 30

31 Measurement Packaging thermal parameters Mount package on a standard test board Mount thermocouple on top of the package center Mount thermacouple on board at the edge of package Put package in a standard test environment Wind tunnel to vary the air speed Apply known amount of power Measure temperature of Tj, Ta, Tb, Tt Calculate Rja, Ψjt, Ψjb Ta Tb Chip Tt Tj Package PCB test board Page 31

32 Measurement Packaging thermal parameters Page 32

33 Measurement Packaging thermal resistance Rjc All heat is removed from top of the package Page 33

34 Measurement Thermal interface material resistance Rcs Page 34

35 Measurement Thermal interface material resistance Rcs Page 35

36 Measurement Heat sink thermal resistance Rsa Air flow T inlet p Heat sink T outlet T 4 p 2 Thermal interface material Copper block Insulation T s T 2 T 3 Heaters Air flow test chamber Nozzle Blower Dimensions are not scaled R sa T s T Q inlet Heat source size: 25 mm x 25 mm T T Q ks A 3 2 s L Page 36

37 Measurement Heat sink thermal resistance Rsa The rmal Re s is tanc e, ( o C/ W ) Test data Present method (Eqs. 6-8) Teertstra [1] Copeland [2] Flow rate (m 3 /s ) Page 37

38 Q & A Page 38

39 Guoping Xu