SLID bonding for thermal interfaces. Thermal performance. Technology for a better society

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Rafe Robert Byrd
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1 SLID bonding for thermal interfaces Thermal performance

2 Outline Background and motivation The HTPEP project Solid-Liquid Inter-Diffusion (SLID) Au-Sn SLID Cu-Sn SLID Reliability and bond integrity Alternative HT TIM technologies comparison Case study HT (>200 C) power controller Stationary performance Conclusions Acknowledgements

The HTPEP project objectives Develop a reliable packaging technology for power electronic systems operating at temperatures up to 250 C. Know-how on SiC component technology.

3 The HTPEP project objectives Develop a reliable packaging technology for power electronic systems operating at temperatures up to 250 C. Know-how on SiC component technology. Processes for packaging of SiC and passive components for HT application. Knowledge on failure mechanisms occurring in interconnects and materials during HT operation. Demonstrator.

4 Application Demonstrate the packaging technology in a power controller for a brushless DC motor for downhole applications. Packaging solution should enable the controller to operate for at least 6 months at an ambient temperature of 200 C and a junction temperature of 250 C.

Die attach and Thermal interface materials (TIM) Typical components Die attach: Fix components to substrate. Low thermal resistance. Electrically conductive.

5 Die attach and Thermal interface materials (TIM) Typical components Die attach: Fix components to substrate. Low thermal resistance. Electrically conductive. TIM 1: Fix substrate mechanically to a support structure. Ensure low thermal resistance. TIM 2: Low thermal resistance between support structure and external housing. TIM 2 Die attach TIM 1

Substrate technology Silicon nitride, Si 3 N 4 Thermal conductivity: up to 90 W/mK CTE: ~3.

6 Substrate technology Silicon nitride, Si 3 N 4 Thermal conductivity: up to 90 W/mK CTE: ~ C Flexural strength: MPa Durable and robust during thermal cycling SiC BJT Cu conductors

7 Die attach/interconnect technology: SLID SLID Solid-Liquid Inter-Diffusion Creates a bond that is stable at higher temperature than the initial process temperature Au-Sn SLID: up to 500 C Cu-Sn SLID: up to 670 C ~10 µm Au-Sn SLID As bonded Cu-Sn SLID As bonded

Solid-Liquid Inter-Diffusion (SLID) Uses a two-metal system: One HT and one LT melting metal. At process temp. above the lower melting point. Inter-diffusion causes IMCs to form. E.g.: Cu-Sn SLID, where a Cu Cu 3 Sn Cu bond is created.

8 Solid-Liquid Inter-Diffusion (SLID) Uses a two-metal system: One HT and one LT melting metal. At process temp. above the lower melting point. Inter-diffusion causes IMCs to form. E.g.: Cu-Sn SLID, where a Cu Cu 3 Sn Cu bond is created. This bond is stable up to 676 C (process temp of C). Before bonding at RT During bonding at T B Hi T m Lo T m Hi T m Hi T m Liquid Hi T m Thin low T m interlayer sandwished between high T m joint parts Melting of low T m interlayer and interdiffusion After bonding at T B Hi T m IMC Hi T m Homogeneous joint / IMC formation where solidification is isothermal

9 Au-Sn SLID Advantages: HT stability and reliability. Oxidation resistant. Relatively low processing temp. Mechanically robust. Au has three functions: Bonding. Diffusion barrier. CTE mismatch absorption. Disadvantages: Novel system relatively unexplored. High cost. Okamoto. H.. Au-sn (Gold-Tin). J. Phase Equilib. Diffus (5): p Liu. H.S.. C.L. Liu. K. Ishida. and Z.P. Jin. Thermodynamic modeling of the Au-In-Sn system. J. Electron. Mater (11): p

Die attach processing Bond Characterization The

100 at% Au Au ζ 90 at% Au10 at% Sn 90 at% Au10 at%

10 Die attach processing Bond Characterization The bond interface is a uniform Au-rich phase. identified by EDS to be the ζ phase (with a melting point of 522 C). 100 at% Au Au ζ 90 at% Au10 at% Sn 90 at% Au10 at% Sn T.A. Tollefsen et al.. "Au-Sn SLID bonding for high temperature applications". HiTEN 2011

11 Die shear strength (MPa) Reliability testing Die shear strength Superb bond strength: >78 MPa. 100 Unaged 500 cycles (0-200 C, 10 C/min) 1000 cycles (0-200 C, 10 C/min) Aged (6 months, 250 C) Substrate Hotplate Chip Clamp MIL-STD-883H 0 SiC Au ζ Au NiP Cu X-section T.A. Tollefsen et al.. "Au-Sn SLID bonding for high temperature applications". HiTEN 2011

12 HT TIM comparison chart Name Material base Effective thermal conductivity (W/m K) Degradation temperature ( C) 300 C Expected final layer thickness (µm) Estimated thermal resistance (mm 2 K/W) Au-Sn SLID Gold and tin 60 T m : ~10 ~0.17 Cu-Sn SLID Copper and tin 104 T m : <10 <0.10 Aptiv 1000 Aptiv 1102 Semi-crystalline polymer film Semi-crystalline polymer film filled with talc Low ( ) 200 Low Duralco 4703 Epoxy with Al 2 O 3 powder % ~50 ~20 Epo-tek 353ND Epoxy % ~4-6 ~40 Epo-tek H74 Epoxy % >50 2 >40 Epo-tek H77 Epoxy % >50 2 >76 Resbond 906 Silicate with magnesia Low ~100 ~17.9 Resbond 931 Silicate with graphite ~100 ~12.5 Resbond 954 Silicate with stainless > Low ~100 ~50 Staystik 581 Silver >3 300 Low Staystik 682 Aluminum nitride >1 300 Low In-plane 2 Particle size

13 Case study Power controller for a brushless DC motor for downhole applications. Motor drive key features: Half bridge topology Switching capability per phase 400 V, 5 A May be combined for 3-phase 3.1 kva total power delivery Power card key specs: Up to 250 C 6 month operation

14 Power card Parts Multilayer capacitors SiC BJT SiC Schottky diode Cu / Ni / Au (Back side) 20 mm Si 3 N 4 substrate 34 mm Ceramic resistors

15 Power card TIM Au-Ge solder Au-Sn SLID SLID or adhesive (Back side) Duralco 4703

16 Power card Dissipation 7 mw 35 mw 10 W 10 mw 700 mw 10 W 350 mw 900 mw (P wire bonds : typically 2 13 mw / bond) (P tot 22 W)

17 Case study BC h = 500 W/m 2 K TIM: Graphite-oil h = 100 W/m 2 K h = 100 W/m 2 K

18 Case study Temperature distribution

19 Case Study Temperature distribution Cu-Sn SLID Duraclo 4703 P = 10 W P = 20 W

20 Case study Temperature drop

21 Case study Temperature drop 10 W SiC BJT T 1 C Die attach (Au-Sn SLID) T < 0.5 C Substrate T 8 C & 7 C TIM: Power card T <0.5 C & 5 C Cu-Sn SLID Duralco 4703 Base plate T 2-3 C TIM: Graphite-oil T < 0.5 C Shell T < 0.5 C Ambient T 5 C SiC BJT Ambient

22 Case study Temperature drop 20 W Substrate T 15 C & 15 C TIM Power card T <0.5 C & 14 C Ambient T 9 C SiC BJT Ambient

23 Case study Derating of TIM specs

24 Case study Temperature profile

25 Potential life time A small reduction in operation temperature may provide a significant improvement in reliability and lifetime of a device. M. Watts "Design Considerations for High Temperature Hybrid Manufacturability". HiTEC 2008

26 Concluding remarks SLID bonding show great TIM potential for high reliability, performance and temperature applications. Primarily due to: Low thermal resistance. Uniform joint (low "contact resistance"). HT stability and reliability Mechanically robust Further investigations of SLID bonding as a TIM is needed. Applicability for larger and more irregular surfaces.

27 Acknowledgements The HTPEP project and its sponsors and partners My co-authors Torleif A. Tollefsen Olav Storstrøm

28 Thanks for your attention! HTPEP Andreas Larsson SINTEF ICT. Instrumentation dept.

Novel Technique for Flip Chip Packaging of High power Si, SiC and GaN Devices. Nahum Rapoport, Remtec, Inc.

Novel Technique for Flip Chip Packaging of High power Si, SiC and GaN Devices Nahum Rapoport, Remtec, Inc. 1 Background Electronic Products Designers: under pressure to decrease cost and size Semiconductor