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V.Sivasubramaniam 1, 2 , J.Janczak-Rusch 1 , J.Botsis 2 , J. Cugnoni 2

Particle reinforced lead-free solders A Comparative study on reinforcing Sn-4Ag-0.5Cu solder with nano and micron sized Cu particles. COST 531 Final Meeting, Vienna,17-05-2007. V.Sivasubramaniam 1, 2 , J.Janczak-Rusch 1 , J.Botsis 2 , J. Cugnoni 2

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V.Sivasubramaniam 1, 2 , J.Janczak-Rusch 1 , J.Botsis 2 , J. Cugnoni 2

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  1. Particle reinforced lead-free soldersA Comparative study on reinforcing Sn-4Ag-0.5Cu solder withnano and micron sized Cu particles COST 531 Final Meeting, Vienna,17-05-2007 V.Sivasubramaniam1, 2, J.Janczak-Rusch1, J.Botsis2, J.Cugnoni2 1-Laboratory of Joining and Interface Technology, EMPA Material Science and Technology, Dübendorf, Switzerland 2-Laboratory of Applied Mechanics and Reliability, EPFL, Lausanne, Switzerland Venkatesh Sivasubramaniam - COST 531 Final Meeting, Vienna,17-05-2007

  2. Overview • Motivation - Composite solders • Materials and processing method • Microstructural analysis of particle reinforced solders • Mechanical properties of solder joints • Failure analysis- Fractography • Conclusion and Future Work Venkatesh Sivasubramaniam - COST 531 Final Meeting, Vienna,17-05-2007

  3. Controlling the growth and formation of intermetallics at the interface (eg. Cu/solder) – during higher service temperature Source:Szu-Tsung Kao et. al , J.Electron. Materials,Vol.35,No.3 (2006) Motivation-Composite approach Venkatesh Sivasubramaniam - COST 531 Final Meeting, Vienna,17-05-2007

  4. Materials used-Current work Matrix alloy Sn-4Ag-0.5Cu (supplied by Alpha metals) Base metal - Standard Cu Reinforcement particles Cu particles 3-20μm Cu2O nano particle 150nm Venkatesh Sivasubramaniam - COST 531 Final Meeting, Vienna,17-05-2007

  5. Chemical reduction route (literature source…) Cu2O Synthesis and Characterization of nano Cu2O particles Venkatesh Sivasubramaniam - COST 531 Final Meeting, Vienna,17-05-2007

  6. Specimen preparation • Manual Mixing of particles with SAC405 paste using mortar • Initially (melt) samples were made in circular (AlN) crucible for microstructural analysis Mortar Venkatesh Sivasubramaniam - COST 531 Final Meeting, Vienna,17-05-2007

  7. Microstructural analysis- SAC405+2 wt% micro Cu Venkatesh Sivasubramaniam - COST 531 Final Meeting, Vienna,17-05-2007

  8. Microstructural analysis- SAC405+2 wt% nano Cu2O All of theCu2O has been converted in to CuSn IMC! Venkatesh Sivasubramaniam - COST 531 Final Meeting, Vienna,17-05-2007

  9. Quality control of joints-X-ray Radiography Step gage from SAC405 cast width of tensile specimen joint Venkatesh Sivasubramaniam - COST 531 Final Meeting, Vienna,17-05-2007

  10. Mechanical Characterization-Reproducibility Venkatesh Sivasubramaniam - COST 531 Final Meeting, Vienna,17-05-2007

  11. Mechanical Characterization-Results Venkatesh Sivasubramaniam - COST 531 Final Meeting, Vienna,17-05-2007

  12. cup and cone ductile fracture! Fractography results of tested composite solder joints nano Cu micro Cu Venkatesh Sivasubramaniam - COST 531 Final Meeting, Vienna,17-05-2007

  13. Mechanical characterization-Aged composite solder joint • Dotted curves –Aged joints isothermally for 24hrs @ 130°C Venkatesh Sivasubramaniam - COST 531 Final Meeting, Vienna,17-05-2007

  14. 20µ 20µ Interfacial IMC of composite solder joint SAC405+2wt% micron-Cu 20µ after ageing before ageing Venkatesh Sivasubramaniam - COST 531 Final Meeting, Vienna,17-05-2007

  15. Microstructural analysis of composite solder joint ‘after’ ageing SAC405+2wt% Nano Cu SAC405+2wt% micron Cu • No appreciable interfacial layer growth for solders with Nano Cu • Cu core was evident even after ageing for samples reinforced with micron Cu Venkatesh Sivasubramaniam - COST 531 Final Meeting, Vienna,17-05-2007

  16. Conslusions • Composite solder prepared with nanometer scale Cu particles are expected to have better creep properties (higher strain rates are achievable) • Potential solution for microelectronics interconnects where good tensile and plastic properties are required • Growth control of interfacial layer for joints made with nanoscale Cu is evident • Mechanism of increase in strain rate for joints with nanoscale Cu reinforcement must still explained Future Work • Creep tests for Composite solders • Ageing for longer duration Venkatesh Sivasubramaniam - COST 531 Final Meeting, Vienna,17-05-2007

  17. Extra slides Venkatesh Sivasubramaniam - COST 531 Final Meeting, Vienna,17-05-2007

  18. Venkatesh Sivasubramaniam - COST 531 Final Meeting, Vienna,17-05-2007

  19. Composite solder joints-Tensile test specimen preparation • 0.5mm gap width, 2wt% reinforcement with microCu and ultrafineCu2O • 4 specimens per batch • Test conditions: • Tensile test-Instron Microtester 5848-cross head speed of 0.5µ/sec • Digital image Correlation (DIC) technique developed by Dr. J.Cugnoni Tensile test specimen-0.5mm gap width DIC setup for localized strain field measurement Venkatesh Sivasubramaniam - COST 531 Final Meeting, Vienna,17-05-2007

  20. Mechanical Characterization-Microhardness (load:200gms,30sec) Venkatesh Sivasubramaniam - COST 531 Final Meeting, Vienna,17-05-2007

  21. (RT) Venkatesh Sivasubramaniam - COST 531 Final Meeting, Vienna,17-05-2007

  22. Venkatesh Sivasubramaniam - COST 531 Final Meeting, Vienna,17-05-2007

  23. Results from previous tests (old temp. profile) Venkatesh Sivasubramaniam - COST 531 Final Meeting, Vienna,17-05-2007

  24. Literature review - Consolidated inferences • The driving force of the moving of the Cu from substrate is due to the concentration difference in solders and substrate • Ni and Cu have similar chemical characteristics,thus their diffusion in Sn is expected to be similar but due to the simultaneus presence of Cu,Ni in Ni reinforced Sn3.5Ag which apparently accelerates formation of (Cu-Ni-Sn) IMC • However since there is not much growth of interfacial layer in Ni reinforced Sn3.5Ag below 100C its quite suitable for applications such as computers where the service conditions are below 100C • Cu6Sn5 particles inhibits the growth of interfacial IMC by increasing the activation energy from 0.8eV to 1.23eV in SnPb • It appears that creep resistance FeSn2 > Ni3Sn4 > Cu6Sn5 > Eutectic SnAg Venkatesh Sivasubramaniam - COST 531 Final Meeting, Vienna,17-05-2007

  25. Microstructural analysis of composite solder joint ‘before’ ageing SAC405+2wt% micron-Cu 10microns SAC405+2wt% ultra fine Cu2O 10microns Venkatesh Sivasubramaniam - COST 531 Final Meeting, Vienna,17-05-2007

  26. Microstructural analysis of composite solder joint ‘after’ ageing SAC405+2wt% nano Cu SAC405+2wt% micron-Cu Venkatesh Sivasubramaniam - COST 531 Final Meeting, Vienna,17-05-2007

  27. nano Cu2O particles Disperse in SAC405 paste Strong flux(OM338) Reflowed at 240°C Cu2O Cu SAC405 reinforced with CuSn(IMC) Venkatesh Sivasubramaniam - COST 531 Final Meeting, Vienna,17-05-2007

  28. Venkatesh Sivasubramaniam - COST 531 Final Meeting, Vienna,17-05-2007

  29. Venkatesh Sivasubramaniam - COST 531 Final Meeting, Vienna,17-05-2007

  30. Quality control of joints-X-ray Radiography X-ray image of step gage Step gage from SAC405 cast Venkatesh Sivasubramaniam - COST 531 Final Meeting, Vienna,17-05-2007

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