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, Bratislava, Slovakia b Institute of Physics, SAS, Dúbravská cesta 9, Bratislava, Slovakia

  Subject of study   Published results   Aim of this contribution   Conclusions

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

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

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) Published results

Solder Sn3.5A g Sn3.5Ag6. 5In Sn3.5Ag 9In  H m [J/g] T xf [°C]  H f [J/g] T xm – T xf [°C] 3327 T xm [°C]  H m,  H f, T xm, T xf are for enthalpy changes and onset temperatures of melting and freezing of relevant solders, respectively Differential scanning calorimetry

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

Shear strength of Cu-solder-Cu joints

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

Shear strenght of Cu-solder-CuCF composite joint

Indium decreases the onset temperature and etnhalpy changes of melting and freezingIndium 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 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 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 between Cu and CF layer where the failure is occured. Joint stregth of Cu-CF composite is lower than that of Cu-Cu due to poor adhesion between Cu and CF layer where the failure is occured. Conclusions

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.

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.

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 Also in interval: RT-180°C : 500 cycles

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

Results Microstructure of original solders: Solder Sn-3.5Ag

Solder Sn-3.5Ag-6.5 In

Solder Sn-3.5Ag-9In

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

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

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

Shear strengths of the Cu-solder-Cu joints

Cu 6 Sn 5 between Cu-Sn3.5Ag solder after uncyceld (a) and 1000 cycles (b) RT – 150 °C Cu 6 Sn 5

Cu 6 Sn 5 between Cu-Sn3.5Ag6.5In solder after uncyceld (a) and 1000 cycles (b) RT – 150 °C Cu 6 Sn 5

Shear strengths of the Cu-solder-Cu joints

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 Cu 6 Sn 5 phase thickness. Joints with solder (2): Shear strength increases with increasing the number of cycles and thickness of Cu 6 Sn 5 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 Cu 6 Sn 5 layer decreases with increasing the number of cycles except for 1000 cycles where InSn4 phase arises instead of In 4 Ag 9. One can suppose that this phase retards the dissolution of copper from Cu 6 Sn 5 phase.The higher is the thickness of Cu 6 Sn 5 layer the lower is the shear strength of the joint. The In 4 Ag 9 phase seems to enhance the dissolution of copper from Cu 6 Sn 5 phase into the SnAg solder.

X-ray phase analyssis of joints with Sn-3.5Ag solder and In In cycles In cycles In cycles In 9 uncycled

Material Number of cycles Phases Sn3.5Ag solder Sn, Ag 3 Sn Sn3.5Ag6.5In solder Sn, In 4 Ag 9 Sn3.5Ag9In solder Sn, In 4 Ag 9, InSn 4 Cu – Sn3.5Ag – Cu joint0 Sn, Cu, Cu 6 Sn 5, Ag 4 Sn, Ag 3 Sn Cu – Sn3.5Ag – Cu joint1000 Sn, Cu, Cu 6 Sn 5, Ag 4 Sn, Ag 3 Sn Cu – Sn3.5Ag6.5In – Cu joint 0Sn, Cu, Cu 6 Sn 5, In 4 Ag 9 Cu – Sn3.5Ag6.5In – Cu joint 1000Sn, Cu, Cu 6 Sn 5, In 4 Ag 9 Cu – Sn3.5Ag9In – Cu joint0 Sn, Cu, Cu 6 Sn 5, Ag 3 Sn,In 4 Ag 9 Cu – Sn3.5Ag9In – Cu joint1000 Sn, Cu, Cu 6 Sn 5, Ag 3 Sn, InSn 4

Conclusion   Sn-3.5Ag-In(0;6.5;9 mass.%) solders consist of Sn and Ag 3 Sn; In 4 Ag 9 and In 4 Ag 9 and InSn 4, 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 Cu 6 Sn 5 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 (Cu 6 Sn 5 ) 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 after cycling   For joint with Sn-3.5Ag-9In solder after 1000 cycles InSn4 phase is formed instead of In4Ag9 phase.