Venkatesh Sivasubramaniam - COST 531 Final Meeting, Vienna, Particle reinforced lead-free solders A Comparative study on reinforcing Sn-4Ag-0.5Cu solder with nano and micron sized Cu particles V.Sivasubramaniam 1, 2, J.Janczak-Rusch 1, J.Botsis 2, J.Cugnoni 2 1 -Laboratory of Joining and Interface Technology, EMPA Material Science and Technology, Dübendorf, Switzerland 2 -Laboratory of Applied Mechanics and Reliability, EPFL, Lausanne, Switzerland COST 531 Final Meeting, Vienna,

Venkatesh Sivasubramaniam - COST 531 Final Meeting, Vienna, 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, Motivation-Composite approach 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)

Venkatesh Sivasubramaniam - COST 531 Final Meeting, Vienna, Materials used-Current work Matrix alloy Sn-4Ag-0.5Cu (supplied by Alpha metals) Base metal - Standard Cu Reinforcement particles Cu particles 3-20μmCu 2 O nano particle 150nm

Venkatesh Sivasubramaniam - COST 531 Final Meeting, Vienna, Synthesis and Characterization of nano Cu 2 O particles Chemical reduction route (literature source…) Cu 2 O

Venkatesh Sivasubramaniam - COST 531 Final Meeting, Vienna, 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, Microstructural analysis- SAC405+2 wt% micro Cu

Venkatesh Sivasubramaniam - COST 531 Final Meeting, Vienna, Microstructural analysis- SAC405+2 wt% nano Cu 2 O All of the Cu 2 O has been converted in to CuSn IMC!

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

Venkatesh Sivasubramaniam - COST 531 Final Meeting, Vienna, Mechanical Characterization-Reproducibility

Venkatesh Sivasubramaniam - COST 531 Final Meeting, Vienna, Mechanical Characterization-Results

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

Venkatesh Sivasubramaniam - COST 531 Final Meeting, Vienna, Mechanical characterization-Aged composite solder joint Dotted curves –Aged joints isothermally for 130°C

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

Venkatesh Sivasubramaniam - COST 531 Final Meeting, Vienna, Microstructural analysis of composite solder joint ‘after’ ageing SAC405+2wt% Nano CuSAC405+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, 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, Extra slides

Venkatesh Sivasubramaniam - COST 531 Final Meeting, Vienna,

Venkatesh Sivasubramaniam - COST 531 Final Meeting, Vienna, Composite solder joints-Tensile test specimen preparation Tensile test specimen-0.5mm gap width 0.5mm gap width, 2wt% reinforcement with microCu and ultrafineCu 2 O 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 DIC setup for localized strain field measurement

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

Venkatesh Sivasubramaniam - COST 531 Final Meeting, Vienna, (RT)

Venkatesh Sivasubramaniam - COST 531 Final Meeting, Vienna,

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

Venkatesh Sivasubramaniam - COST 531 Final Meeting, Vienna, 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 Cu 6 Sn 5 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 FeSn 2 > Ni 3 Sn 4 > Cu 6 Sn 5 > Eutectic SnAg Literature review - Consolidated inferences

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

Venkatesh Sivasubramaniam - COST 531 Final Meeting, Vienna, Microstructural analysis of composite solder joint ‘after’ ageing SAC405+2wt% nano CuSAC405+2wt% micron-Cu

Venkatesh Sivasubramaniam - COST 531 Final Meeting, Vienna, nano Cu 2 O particles Disperse in SAC405 paste Strong flux(OM338) Reflowed at 240°C SAC405 reinforced with CuSn(IMC) Cu 2 OCu

Venkatesh Sivasubramaniam - COST 531 Final Meeting, Vienna,

Venkatesh Sivasubramaniam - COST 531 Final Meeting, Vienna,

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