Test stand for the Characterisation of Thermal Interface Materials from the macro level up to the nano level

Transcription

1 13th LEIBNIZ CONFERENCE OF ADVANCED SCIENCE April 2012 NANOSCIENCE 2012 Test stand for the Characterisation of Thermal Interface Materials from the macro level up to the nano level Mohamad Abo Ras Berliner Nanotest und Design GmbH and Fraunhofer Institute for Electronic Nanosystems (ENAS) Page 1

2 Outline Application of Thermal interface Materials Characterization of thermal interface materials New platform for different modules for the characterization of TIM Characterization capabilities Interesting results Summary Page 2

3 Motivation Page 3

4 Applications of thermal interface materials Examples of TIM applications TIM1 (die to package or to heat spreader) TIM2 (package or heat spreader to heat sink) Solder and Underfill Type of TIMs: Grease, adhesive, pad, gap filler, solder, mono metal, etc. Electrical conductive, electrical insulating Source: Shin-Etsu Aims & Challenges High thermal conductive Low thermal interface resistance Low bond line thickness Large contact area Source: Nanopack Page 4

5 Importance of Thermal Interface Materials Market analysis for Thermal Interface Materials & Thermal Management Technologies Market size: +10.3%/year: 6.8 B in B in 2013 Market share: In 2007: Computer industry: 57%, Telecom: 16% In 2013: Medical: 12%, Office electronics: 12% Main actors: Bergquist, Chomerics, Thermalloy, Lytron, Power Devices, DoW Corning, Shin Etsu, Denka, Arctic Silver, Wacker Chemie, Thermarcore, Hereaus,... field of application Avionics Aerospace High Brightness LEDs Power electronics. Microprocessor Data centers Automotive Etc. Page 5

6 Example: Power Transistors TO-220 Package: typically used for power MOSFETs, IGBTs, Bipolar Transistors, etc. Gate Junction Buried Oxide Silicon substrate TIM 1 Lid / Spreader TIM 2 T Junction R thj-c T Case Heatsink R thc-a Sources: specification sheet of ST Microelectronics L78xxAB series of regulators Ambient T Ambiant Thermal Interface Materials and Heatsinks represent more than 90% of the thermal resistance Page 6

7 Nanotechnologies to improve heat transfer Multi modal particles Polymer fibres & metallic alloy Surface microstructuring Nano sponge interfaces Vertically aligned CNT Nano-scale optimization TIM optimization Surface optimization Nano-scale optimization Increase thermal conductivity Increase thermal conductivity Reduce BLT Reduce interface resistance Increase thermal conductivity Improve phonon transfer Advanced technologies need advanced test systems Page 7

8 Characterization of Thermal Interface Materials Page 8

9 Methods for Characterization of TIMs Transient methods Transient Flash Steady state methods ASTM-D5470 Synthesized dynamic models JESD 51: Thermal measurement of component packages Disadvantage of ASTM D5470: No real conditions, use two Cu bar No characterization of adhesives or solders No in-situ measurement of BLT Samples are tested under high pressure Page 9

10 Characterization of Thermal Interface Materials R th,int1 R th,tim Basic principle Rth, eff T Q R th, eff th,int1 th, TIM th,int2 R th, eff R R th,0 R 1 d A bulk R R th,int2 y b a x 10 Gel TIM #1 Bulk and interface contribute to Rth R th [K/W] R th, λ TIM Folie#2 Linear function d [mm] Page 10

11 The New Platform with different Modules TIMA-Platform Testing of nonadhesive TIMs Testing of adhesive TIMs High accuracy testing Testing of highly conductive TIMs Reliability testing of TIMs Costumer specific modules Page 11

12 TIMA Platform Water cooler Stepper motor Incline sensors 30 arcsec resolution LVDT Distance mester 1µm resolution Incline sensor 2 axes Goniometer Load cell Load cell 2 axesgoniometer ± 200N 30 arcsec resolution Incline sensor Modul e Water cooler L V D T Stepper motor 0,25µm steps case PMMA Universal platform for different modules for characterization of all types of TIMs Page 12

13 Standard characterization of TIMs T Module for adhesive TIMs Heater T1 T2 T3 T4 T5 T6 TIM Metal socket Metal socket Water cooler Q Following values and dependences can be calculated by these modules bulk eff Rth 0 Rth Rth Rth f f f f T p Rz p T Module for non-adhesive TIMs Thermal test chip Tc TIM T1 T2 Metal socket T3 Water cooler Q TIM socket Micrometer screw aligning plug spring Tool for assembling of thermal adhesives Aluminium socket Characterization under real conditions Different configurations possible depending on desired contact partners, i.e. Al, Cu or Si Measuring the actually heat flux Design allows to incorporate analysis by FIB, SEM and/or EDX Rapid test method using a test socket Curing at high temperature is possible T=180 C Low cost testing (test socket < 50 ) In situ measurement of BLT and pressure Page 13

14 Assessment of Accuracy and Parasitic of TIMA Tester Total Error Evaluation Temperature measurement by TTC and NTC Need high accuracy calibration Need precise constant current source Heat flux measurement Geometry of metal socket Thermal conductivity of metal socket Form of T-sensors (NTC) Accuracy of T-Sensors Very High High T Tc T1 T2 T3 Thermal test chip TIM Metal socket Water cooler Q BLT measurement use high accuracy LVDT Tilt use goniometers and tilt sensors Convection and radiation Free convection by use protective case Radiation checked by IR-Camera High Highmedium Low T T1 T2 T3 T4 T5 T6 Heater TIM Metal socket Metal socket Water cooler Q Page 14

15 Accuracy of temperature measurement NTC-Sensors: Adapted design (Cylinder, 1mm diameter) Non-linear behavior (should be calibrated for the range of use) TTC-Sensors: Adapted design (flat, full area heater) Diode as T-sensor, linear behavior , NTC 3,4 3,3 R [ ] U [V] 3,2 3, , , T [ C] T [ C] Page 15

16 High precision calibration chamber calibration process (exemplary) -20 C < T < 175 C Avg. heating rate 10 K/min Avg. cooling rate 5 K/min Accuracy < 0.01 K multiple parallel measurement greatly insulated chassis (< 0.01 W/mK) water cooling 37-pin data bus 350W power (heating / cooling) Page 16

17 Reproducibility of the measurement One TIM was measured 10-times under: Same BLT Same pressure Same temperature In different times Variation < 5% Page 17

18 Interesting results measured by standard modules What can be measured by these modules? Page 18

19 Standard characterization of greases R th,eff [K/W] 2,4 2,2 2,0 1,8 1,6 1,4 1,2 1,0 0,8 0,6 0,4 0,2 λ=5 W/mK BLT min =600µm Rth min =1.2 K/W 0, λ=2 W/mK BLT min =50µm Rth min =0.1 K/W BLT [µm] λ=5 W/mK BLT min =100µm Rth min =0.1 K/W Bulk λ is the half of the story Rth 0 and min BLT are very important T Tc T1 T2 T3 Thermal test chip TIM Metal socket Water cooler Q Page 19

20 Standard characterization of adhesives Aluminium socket R th,eff [K/W] λ=1 W/mK λ=7 W/mK BLT [µm] TIM T socket Micrometer screw aligning plug spring Tool for assembling of thermal adhesives T1 T2 T4 T3 T5 T6 Heater TIM Metal socket Metal socket Water cooler Q Page 20

21 Influence of temperature on thermal conductivity 4,0 One thermal grease Measured at different temperatures (50 C, 70 C, 90 C and 110 C) T on TIM [ C] λ bulk [W/mK] Rth 0 [mm² K/W] 50 4,9±0,1 10±3 70 4,5±0,1 13±3 90 4,2±0,1 14± ,9±0,1 11±3 R th,eff [K/W] 3,5 3,0 2,5 2,0 1,5 1,0 0,5 50 C 70 C 90 C 110 C BLT [µm] λ 25 differences at thermal conductivity between 50 C and 110 C Unfortunately lower performance at higher temperature Page 21

22 Thermal resistance as function of pressure 3,0 Three thermal greases were measured under different pressures 100 kpa 700kPa Rth=f(p) d=f(p) Further options: Pressures from 0 to 2 MPa are possible Bond line thickness as function of pressure at different temperatures d [µm] Rth,eff [K/W] 2,5 2,0 1,5 1,0 0, p [kpa] p [kpa] Page 22

23 Influences of curing conditions on thermal conductivity of thermal adhesives eff [W/mK] eff [W/mK] ,3 1,2 1,1 1,0 0,9 0,8 0,7 0,6 0,5 0,4 0,3 0,2 0,1 0,0 MD140 PC3001 1K/min 10K/min 1K/min 10K/min Curing speed SHT6F (150 C) SHT6F (170 C) 1K/min 10K/min 1K/min 10K/min Curing speed Temp. [ C] Al Curingprofiles with different heating rates 10 K/min 1 K/min MD140_1K/min Adhesive High lambda Al 20µm 4µm Time [min] Al 10 K/min 1 K/min MD140_10K/min Adhesive low lambda Al 20µm 4µm Page 23

24 Further module accelerated in-situ measurement of reliability and aging behavior of thermal interface materials Page 24

25 Background Low thermal mismatch Low thermal mismatch High thermal mismatch T Nonadhesive TIM Adhesive TIM Pump out or Dry out Substrate TIM Die Heat sink Delamination or crack Page 25

26 Measuring principle (Patented) Steppe r motor Variation of BLT or pressure by stepper motor In situ measurement of BLT and pressure In situ measurement of thermal resistance of TIM Computer controlled long term testing Incline sensor 2 axes Goniometer Kompression Expansion Incline sensor Load cell Thermal test chip TIM Metal socket L V D T Δp or Δd F TTC TIM MS TTC TIM MS Expansion time Kompression Water cooler Schematic of the long term testing ΔR th time Page 26

27 Further module Characterization of highly conductive TIMs Page 27

28 Silver Sintering for High-Lambda Connection AlN T, p, t 4 Oppermann, Hutter, Klein, IZM Berlin Chip on DCB SAM Page 28

29 Microstructure of Silver - Die Bond, Sintered Sintered Plated 1 µm 1 µm Low T,p,t sintering High T,p,t sintering highly porous continous µ-structure, grain formation Different process parameters (T, p, t) produce different microstructrures Oppermann, Hutter, Klein, IZM Berlin Technology development necessary Page 29

30 Characterization: High Lambda Test stand contact area for Ag-Joint Specimen, used as in real die-bonding process with Ag-metalisation, d by x-sect Vacuum chamber for thermal char (1 mbar) Schematic for high-lambda Tester (Cu meas. by laserflash) Accuracy < ± 5 %, equivalent to ± 10 W/mK at possible 420 W/mK for pure Ag Correlation to simulation T along Cu-bars of Specimen Page 30

31 Sample # Influences of sintering forces on thermal and mechanical properties of sinter silver Sintering force[n] Shear force[n] BLT [µm] Area [mm²] λ [w/mk] , , Sintered at 270 C λ [w/mk] 180±10 Sample 60N Sample 90N 1µm Sample 60N Sample 90N 10µm Sample 60N Sample 90N 2µm ,20 n.a , ±20 1µm 10µm 2µm , , ±30 Sample 120N Sample 120N Sample 120N [W/mK] Thermal conductivity Shear force sintering force [N] F [N] LM of shear area 1µm LM of gross section Higher sintering forces lead to: higher thermal conductivity higher shear forces 10µm FIB of gross section due to densification and microstructure evolution 2µm Page 31

32 Further module High Accuracy Characterization Module Characterization of small effects e.g. surface modification by nanotechnologies Page 32

33 Nanosponge Technology Apply on Si-die on wafer level Au Nanosponge Plating Alloy Dealloying 2 µm Au massive Oppermann, Wunderle, IZM Berlin Plating base Cu Page 33

34 Nanosponge Structure open porous 15 nm pores 20 %vol Au 300 nm Oppermann, Wunderle, IZM Berlin FIB image of the nano-sponge Au-structure Page 34

35 Thermal Enhancement by Nanosponge Thermal Enhancement Potential hi Au density hi-λ large contact area low Rth,0 Compressibility Roughness Surface Energy Conforming to filler particles reduces R th,0 at interfaces, excess adhesive can be aborbed <> point contact Increased mechanical interlocking for Adhesives on Au Surfaces (few 10 nm are enough) Interdiffusion possible for contact formation (nano-scale effect) Structure tuneable mechanical properties tuneable Page 35

36 Most Accurate Characterization Method: Si-TIM-Si T-Sensors AlN- substrate Thin film heater F CVD Ox Equipotential surfaces AlN- substrate Ceramic Substrate Nanosponge both sides Front Wire-bond Si TIM Si Micro water cooler bumps Back Local heat flow sensor Local T sensor Nanosponge Local thickness sensor Thin film T- and j - Sensor Glass passivation, double sided Page 36

37 Summary Adhesives pads Substrates Greases Solder Mono metal TIMs can be measured PCM Film Gap Filler Rth=f(T) Rth=f(p) Rth=f(Rz) Values can be measured λ Bulk Rth 0 Rth eff Rth=f(t) Rth=f(process) λ eff Page 37

38 Thank you very much for your attention! Time for questions? Some of this work was carried out within the BMBF Project CharTIM This funding is gratefully acknowledged Contact: Page 38