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Subject of study Published results Aim of this contribution Conclusions

Influence of thermal cycling on shear strength of Cu – Sn3.5AgIn – Cu joints with various content of indium Pavol Šebo a , Peter Švec b , Dušan Janičkovič b , Pavol Štefánik a a Institute of Materials and Machine Mechanics, SAS, Račianska 75, 831 02 Bratislava, Slovakia

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Subject of study Published results Aim of this contribution Conclusions

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  1. Influence of thermal cycling on shear strength of Cu – Sn3.5AgIn – Cujoints with various content of indium Pavol Šeboa, Peter Švecb, Dušan Janičkovičb, Pavol Štefánika a Institute of Materials and Machine Mechanics, SAS, Račianska 75, 831 02 Bratislava, Slovakia b Institute of Physics, SAS, Dúbravská cesta 9, 845 11 Bratislava, Slovakia

  2. Subject of study • Published results • Aim of this contribution • Conclusions

  3. COST 531: Lead-free solder materials: From many material combinations for study of low temperature lead-free solder we chose on the base of literature data Sn-Ag based alloys

  4. Subject of study To characterize the effect of indium addition in lead-free Sn – 3.5Agsolder on its • phase transition temperature, • wetting of copper substrate • shear strength of copper joints.

  5. Published results Part of the results were presented at the COST 531 meetings in Lausanne and Genoa Most of the results were published in Kovove Mater. 43 (2005) 202-209

  6. Solder Sn3.5Ag Sn3.5Ag6.5In Sn3.5Ag9In Txm[°C] 225 209 206 Hm[J/g] 67 60 61 Txf[°C] 192 182 181 Hf[J/g] -64 -60 -59 Txm – Txf [°C] 33 27 25 Differential scanning calorimetry Hm, Hf , Txm, Txf are for enthalpy changes and onset temperatures of melting and freezing of relevant solders, respectively

  7. Indium concentration dependence of contact angle of solders on Cu substrate for various temperatures

  8. Shear strength of Cu-solder-Cu joints

  9. composite Cu foil Sn3.5Ag6.5In 280°C, 30 min. Cu-solder-CuCF composite joint

  10. Shear strenght of Cu-solder-CuCF composite joint

  11. Conclusions • Indium decreases the onset temperature and etnhalpy changes of melting and freezing • Wetting angle between copper substrate and SnAgIn solder decreases with increasing amount of In and wetting temperature and time • Joint strength moderately decreases with increasing joining temperature and the amount of In. Failure of joints occures in solder. • Joint stregth of Cu-CF composite is lower than that of Cu-Cu due to poor adhesion betweenCu and CF layer where the failure is occured.

  12. The aim of this paper is: •     to recognize the microstructure changes in Sn-3,5Ag solders and joints of Cu-Cu •  to identified the intermetallic compounds in the Cu – solder – Cu pad interfaces • to determine the effect of thermal cycling on the degradation in residual shear strength of Cu – Sn-3.5Ag-In – Cu joints • with various amount of indium.

  13. Materials Solders: Lead-free solder alloys contained: 0 (1); 6.5(2) and 9(3) mass % In Produced in bulk form (for wetting experiments) and by rapid quenching in the ribbon form 5 mm wide and ~0.05mm thick (for Cu-solder-Cu joints) Substrates: Cu plates prior to placing with solder into the holder and furnace were daubed with rosin moderately activated flux.

  14. Joints: Joints-four for each set of cycling-were prepared at 280°C and 1800 s in the air atmosphere:  One specimen was used for microstructure study, three for shear strength measurement Cycling: Cycling was done in air atmosphere in the temperature interval: RT – 150°C; Number of cycles: 100; 200; 500 and 1000. Also in interval: RT-180°C : 500 cycles

  15. Investigation (of solders, joints, interface in joint):  • Microstructure: light and scanning electron microscopy (SEM), energy disperse X-ray analyzer (EDAX), • X-ray diffraction (CuK radiation) • Influence of thermal treatment on solders: • Resistometry: planar furnace with 4 probes method •  Shear strength: Zwick testing machine, push-off method

  16. Results Microstructureof original solders: Solder Sn-3.5Ag

  17. Solder Sn-3.5Ag-6.5 In

  18. Solder Sn-3.5Ag-9In

  19. In 0 In 6.5 In 9 X-ray phase analyssis of Sn-3.5Ag solders with In

  20. Temperatuture dependence of the resistance of the Sn-3.5Ag solder with In

  21. All three solders heated In0 – up to 180 °C In6.5 – up to 160 °C In9 – up to 180 °C and quenched X-ray diffraction : No change in phase composition SEM: coarsening of microstructure in In6.5 and In9

  22. Shear strengths of the Cu-solder-Cu joints

  23. Cu6Sn5 Cu6Sn5 between Cu-Sn3.5Ag solder after uncyceld (a) and 1000 cycles (b) RT – 150 °C

  24. Cu6Sn5 Cu6Sn5 between Cu-Sn3.5Ag6.5In solder after uncyceld (a) and 1000 cycles (b) RT – 150 °C

  25. Shear strengths of the Cu-solder-Cu joints

  26. Shear strength of Cu-solder-Cu joints for 100,200,500 and 1000 cycles (including shear strength of no cycled joints).  Joints with solder (1): Shear strength decreases with increasing amount of cycles. This decrease reflects the increase of Cu6Sn5 phase thickness.  Joints with solder (2): Shear strength increases with increasing the number of cycles and thickness of Cu6Sn5 layer decreases.  Joints with solder (3): Shear strength increases except for 1000 cycles (where shear strength is on the level of no cycled joint). The thickness of Cu6Sn5 layer decreases with increasing the number of cycles except for 1000 cycles where InSn4 phase arises instead of In4Ag9.  One can suppose that this phase retards the dissolution of copper from Cu6Sn5 phase.The higher is the thickness of Cu6Sn5 layer the lower is the shear strength of the joint. The In4Ag9 phase seems to enhance the dissolution of copper from Cu6Sn5 phase into the SnAg solder.

  27. In 0 1000 cycles In 6.5 1000 cycles In 9 1000 cycles In 9 uncycled X-ray phase analyssis of joints with Sn-3.5Ag solder and In

  28. Material Number of cycles Phases Sn3.5Ag solder Sn, Ag3Sn Sn3.5Ag6.5In solder Sn, In4Ag9 Sn3.5Ag9In solder Sn, In4Ag9, InSn4 Cu – Sn3.5Ag – Cu joint 0 Sn, Cu, Cu6Sn5, Ag4Sn, Ag3Sn Cu – Sn3.5Ag – Cu joint 1000 Sn, Cu, Cu6Sn5, Ag4Sn, Ag3Sn Cu – Sn3.5Ag6.5In – Cujoint 0 Sn, Cu, Cu6Sn5, In4Ag9 Cu – Sn3.5Ag6.5In – Cu joint 1000 Sn, Cu, Cu6Sn5, In4Ag9 Cu – Sn3.5Ag9In – Cu joint 0 Sn, Cu, Cu6Sn5, Ag3Sn,In4Ag9 Cu – Sn3.5Ag9In – Cu joint 1000 Sn, Cu, Cu6Sn5, Ag3Sn,InSn4

  29. Conclusion • Sn-3.5Ag-In(0;6.5;9 mass.%) solders consist of Sn and Ag3Sn; In4Ag9 and In4Ag9 and InSn4, respectively. • In all joints before and after thermal cycling in the temperature interval RT-150°C as well as RT-180°C at the interface between copper substrate and the solder Cu6Sn5 phase is formed. • For the joints made with indium-free solder the thickness of this phase is growing with increasing the number of cycles and the shear strength of these joints is decreasing. • For the joints made with In containing solders the thickness of this phase (Cu6Sn5) is decreasing with increasing the number of cycles and the shear strength of these joints is increasing. • Contents of phases in joints made with Sn-3.5Ag and Sn-3.5Ag-6.5 mass% In is equal before and aftercycling • For joint with Sn-3.5Ag-9In solder after 1000 cycles InSn4 phase is formed instead of In4Ag9 phase.

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