SLID bonding for thermal interfaces Thermal performance
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. Processes for packaging of SiC and passive components for HT application. Knowledge on failure mechanisms occurring in interconnects and materials during HT operation. Demonstrator.
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. www.bxpl.com
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: ~3.2 ppm/k @ 250-300 C Flexural strength: 750-900 MPa Durable and robust during thermal cycling SiC BJT Cu conductors
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. This bond is stable up to 676 C (process temp of 250-300 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
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.. 2007. 28(5): p. 490-490. Liu. H.S.. C.L. Liu. K. Ishida. and Z.P. Jin. Thermodynamic modeling of the Au-In-Sn system. J. Electron. Mater.. 2003. 32(11): p. 1290-1296.
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
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 80 60 40 20 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
HT TIM comparison chart Name Material base Effective thermal conductivity (W/m K) Degradation temperature ( C) Outgassing @ 300 C Expected final layer thickness (µm) Estimated thermal resistance (mm 2 K/W) Au-Sn SLID Gold and tin 60 T m : 522 - ~10 ~0.17 Cu-Sn SLID Copper and tin 104 T m : 676 - <10 <0.10 Aptiv 1000 Aptiv 1102 Semi-crystalline polymer film Semi-crystalline polymer film filled with talc 0.25 200 Low 8 32 0.43 (0.91 1 ) 200 Low 12 28 Duralco 4703 Epoxy with Al 2 O 3 powder 2.55 330 0.33% ~50 ~20 Epo-tek 353ND Epoxy 0.10-0.15 412 0.87% ~4-6 ~40 Epo-tek H74 Epoxy 1.25 425 0.80% >50 2 >40 Epo-tek H77 Epoxy 0.66 405 1.47 % >50 2 >76 Resbond 906 Silicate with magnesia 5.6 1650 Low ~100 ~17.9 Resbond 931 Silicate with graphite 8 3000 - ~100 ~12.5 Resbond 954 Silicate with stainless >2 1200 Low ~100 ~50 Staystik 581 Silver >3 300 Low 38 12.7 Staystik 682 Aluminum nitride >1 300 Low 38 38 1 In-plane 2 Particle size
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
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
Power card TIM Au-Ge solder Au-Sn SLID SLID or adhesive (Back side) Duralco 4703
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)
Case study BC h = 500 W/m 2 K TIM: Graphite-oil h = 100 W/m 2 K h = 100 W/m 2 K
Case study Temperature distribution
Case Study Temperature distribution Cu-Sn SLID Duraclo 4703 P = 10 W P = 20 W
Case study Temperature drop
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
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
Case study Derating of TIM specs
Case study Temperature profile
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
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.
Acknowledgements The HTPEP project and its sponsors and partners My co-authors Torleif A. Tollefsen Olav Storstrøm
Thanks for your attention! HTPEP Andreas Larsson SINTEF ICT. Instrumentation dept. andreas.larsson@sintef.no