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

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 17-18 May 2007

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 ≈ 10 -5 Pa Tl+ 50 K <Texp< 1300 K Final Meeting COST Action 531 Vienna 17-18 May 2007

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 17-18 May 2007

Surface Tension Results Final Meeting COST Action 531 Vienna 17-18 May 2007

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 17-18 May 2007

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 17-18 May 2007

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 17-18 May 2007

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

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 17-18 May 2007

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 17-18 May 2007

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 17-18 May 2007

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 17-18 May 2007

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 17-18 May 2007

Thank for your attention Final Meeting COST Action 531 Vienna 17-18 May 2007