1. E. Ricci, D. Giuranno, F. Gnecco, S. Amore, T. Lanata, R. Novakovic
Surface properties and wetting characteristics of lead-free solder alloys
E. Ricci, D. Giuranno, F. Gnecco, S. Amore, T. Lanata, R. Novakovic
National Research Council (CNR) – Institute for Energetics and Interphases (IENI)
Genoa - Italy

2. Final Meeting COST Action 531 Vienna 17-18 May 2007
Contribution from IENI Genova to COST 531
Characterization Surface Properties and wetting behaviour of Selected groups of Lead-free Alloys as Soldering Materials
Surface Tension + modelling:
Binary systems Ag-Cu Au-Sn
Cu-Sn Au-In
In-Sn Bi-In
Wetting behaviour:
Ternary systems: Au-In-Sn/Cu
Bi-In-Sn/Cu
Binary sub-systems: Au-In/Cu Bi-In /Cu
Au-Sn/(Cu,Ni) In-Sn /(Cu,Ni) Cu-Sn/(Cu,Ni)
Final Meeting COST Action 531 Vienna May 2007

3. Preparation of the samples
Experimental
Preparation of the samples
Preparation of the alloys from the pure elements by melting in a clean atmosphere
Control of alloys compositions by SEM-EDS
Mass of alloy sample mechanical and chemical cleaned
3.0 g ST measurements
1.0 g wetting experiments
Working Conditions
Surface Tension Measurements
Wetting Experiments
Cu, Ni square plate (13x13x1mm) metallogrhaphically mirror polished (Ra<0.05 mm)
Ar N60 atmosphere PO2 ≤ 10-6 Pa
Texp = Tl+ 50 K up to 900K
Sapphire crucible
Clean Conditions
Flux Ar N60 atmosphere 10-4 < PO2<10-2 Pa; Vacuum conditions Ptot ≈ Pa
Tl+ 50 K <Texp< 1300 K
Final Meeting COST Action 531 Vienna May 2007

4. Final Meeting COST Action 531 Vienna 17-18 May 2007
Experimental
Temperature
Surface Tension
Oxygen Partial Pressure
Contact Angles
Acquisition of drop profile in real time (2 s) by ASTRAview® appropriate Software
g SV = g LS + g LV cos q
g SV
g LV
g LS
Liquid
q < 90°
wettability
q > 90°
no wettability
Final Meeting COST Action 531 Vienna May 2007

5. Surface Tension Results
Final Meeting COST Action 531 Vienna May 2007

6. Theoretical calculations of the surface tension
Au-In
Au-Sn
at%Au
at%Au
Experimental determination of the surface tension
Experimental data are in good agreement with surface tension values calculated using different theoretical models
Theoretical calculations of the surface tension
Final Meeting COST Action 531 Vienna May 2007

7. Theoretical calculations of the surface tension
Bi-In
In-Sn In
at%In
at%In Bi
Experimental determination of the surface tension
Experimental data are in good agreement with surface tension values calculated using different theoretical models
Theoretical calculations of the surface tension
Final Meeting COST Action 531 Vienna May 2007

8. Theoretical calculations of the surface tension
Cu-Sn
Ag-Cu
at%Cu
at%Cu
Experimental determination of the surface tension
T=1373K
1 REG. SOL
2 Prasad’smodel
□ Exp Results
Theoretical calculations of the surface tension
Final Meeting COST Action 531 Vienna May 2007

9. Final Meeting COST Action 531 Vienna 17-18 May 2007
Wetting Results
Final Meeting COST Action 531 Vienna May 2007

10. Final Meeting COST Action 531 Vienna 17-18 May 2007
Wetting Results
Composition [at%]
Temperatures [K]
Substrates Tl Tf Ni Cu
qf[°]
qf [°]
In-70Sn
450
710 20 41
In-85Sn
529 30 23
Au – 55 In
768
852 50
Au – 97 In
588
760 21
Au-82Sn
582 34
Cu-70Sn
813
910 26
<5
Cu-80Sn
743 25
Cu – 90 Sn
653 10
Cu-95Sn
583
Bi – 52 In
383
623 51
Bi – 80 In
355
648 44
Au – 5 In – 81 Sn
538
645 33
Au – 11 In – 84 Sn
493
600 52
Au – 8 In – 88 Sn
503
602 39
Bi – 5 In – 81 Sn
483
608
Bi – 8 In – 88 Sn
430
Final Meeting COST Action 531 Vienna May 2007

11. Interface Characterization
Cu substrate
h-Cu6Sn5 based phase
e-Cu3Sn based phase
 60 mm
In – 70Sn
Similar behaviour:
Cu-Sn/Ni
Au-In-Sn/Cu
Ni substrate
Ni3Sn4 based phase
 14 mm
As Pb-Sn solder alloys these systems show:
Formation of a layer (<100 mm) of intermetallic compounds at the interface between solder alloys and substrate
These reactions are dominated by the Sn-component, but the h and the e-phase are exchanged
Final Meeting COST Action 531 Vienna May 2007

12. Interface Characterization
Excessive dissolutive wetting
Cu substrate
Au-55In
Erosion of the substrate and Increase in the total volume
of liquid phase Cu
Negative influence on mechanical and electrical properties
Similar behaviour:
Cu-Sn/Cu
Final Meeting COST Action 531 Vienna May 2007

13. Interface Characterization
Bi-52In
Cu substrate
BiIn2 Cu
Interface macroscopically planar
Similar behaviour:
Au-Sn/(Cu,Ni)
Bi-In-Sn/Cu
Weakness of solder joint
Final Meeting COST Action 531 Vienna May 2007

14. Final Meeting COST Action 531 Vienna 17-18 May 2007
Conclusions
Complete characterization of the surface properties and the wetting behaviour of selected groups of lead-free solder alloys
In-Sn and Cu-Sn are good candidates as basic systems for new lead free solders concerning their wettability on Cu and Ni
The additional elements should be chosen in order to preserve the wetting properties to exchange the e and h phase formation at the interface, and inhibit the excessive growth of a reactive layer keeping good mechanical and electrical properties
Final Meeting COST Action 531 Vienna May 2007

15. Thank for your attention
Final Meeting COST Action 531 Vienna May 2007