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Physical and Mechanical Characteristics of Pb -free Solder - Copper Joints

Physical and Mechanical Characteristics of Pb -free Solder - Copper Joints. J. Janczak-Rusch* , T. Rütti* , A. Mellal @ and John Botsis @ *EMPA; @ EPFL. Within the framework of :Cost Action 531:. Project funded by OFES (Switzerland).

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Physical and Mechanical Characteristics of Pb -free Solder - Copper Joints

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  1. Physical and Mechanical Characteristics of Pb-free Solder-Copper Joints J. Janczak-Rusch* , T. Rütti*, A. Mellal@ and John Botsis@ *EMPA; @EPFL Within the framework of :Cost Action 531: Project funded by OFES (Switzerland)

  2. New generation particle reinforced Pb-free solders: initial tests • Experimental setup • tensile test specimen dimensions: 20mm x 1mm cross section • solder alloy: Sn-3.5Ag-0.5 Cu • soldering cycle: 6 min ( 30 s) to melt, 1 min ( 10 s) in liquid phase, fast cooling (solder jig placed into water); peak temperature: 230°C • tensile test conditions: Instron 5848 MicroTester in displacement control mode at 1µm/s; strain measured with a 50mm clip gauge • Test matrix • effect of solder gap width: 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.8 and 1.0mm • effect of room temperature ageing (TH= 0.6): 1day, days, 1 week, 2 weeks, 1 month, 2 months • effect of ageing at elevated temperatures: 1 week and 2 weeks at TH =0.75 and TH = 0.9

  3. Thermal cycling

  4. Mechanical testing h = 50 mm b = 20 mm e = 1 mm t = variable

  5. Preliminary results • Results • a notable number of gas pores form in the solder joint under the given soldering conditions • yield stress, tensile stress, Young’s modulus and strain at fracture are not significantly influence by ageing at room temperature • ageing at high temperatures reduces yield and tensile strengths and increases strain (ductility) • decreased solder gap width increases yield and tensile strengths and decreases strain (ductility)

  6. Typical microstructures cross-section (etched) typical fracture surface Sn-4.0Ag-0.5Cusolder joint

  7. Finite Element Analysis • Purpose • Numerical simulation of solder joints mechanical behavior • Model description: • Geometry (h = 50 mm, extensometer’s length) • Boundary conditions: same as experiment, T=25°C • FE Mesh (Plane stress, 2 axial symmetries) • Constitutive law • Copper: Elastoplastic (E=112 GPa, n=0.33, sy=69 MPa) • Solder: elasto-viscoplastic (E=56 GPa, n=0.35, sy=32.5 MPa) • creep: Garofalo’s type power law

  8. Finite Element Analysis Calibration of constitutive model:

  9. Finite Element Analysis Simulation of different thickness specimen:

  10. New generation particle reinforced Pb-free solders • Next steps • soldering under vacuum/ reduced pressure to eliminate gas pores • testing of different base solder alloys: Sn-Ag and Sn-Cu compared to Sn-Ag-Cu • incorporation of strengthening particles into solder alloy

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