Surface properties and Surface properties and wetting characteristics of wetting characteristics of

lead-free solder alloyslead-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

Contribution from IENI Genova to COST 531Contribution 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-InIn-Sn Bi-In

Wetting behaviour:Ternary systems: Au-In-Sn/Cu

Bi-In-Sn/CuBinary sub-systems: Au-In/Cu

Bi-In /CuAu-Sn/(Cu,Ni)In-Sn /(Cu,Ni)Cu-Sn/(Cu,Ni)

Final Meeting COST Action 531 Vienna 17-18 May 2007

Preparation of the samplesPreparation 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 ConditionsWorking Conditions

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

Surface Tension MeasurementsSurface Tension Measurements

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

Wetting ExperimentsWetting Experiments

ExperimentalExperimental

Final Meeting COST Action 531 Vienna 17-18 May 2007

ExperimentalExperimental

Surface TensionSurface Tension

Contact AnglesContact Angles

Acquisition of drop profile in real time (2 s) by ASTRAview®

appropriate Software

Oxygen Partial Pressure

Temperature

Final Meeting COST Action 531 Vienna 17-18 May 2007

SV = LS + LV cos

< 90°wettability

> 90° no wettability

S

V

LV

LS

Liquid

Final Meeting COST Action 531 Vienna 17-18 May 2007

Surface Tension ResultsSurface Tension Results

Temperature [K]

1273 1323 1373 1423 1473 1523

Sur

face

Ten

sion

[mN

/m]

400

500

600

700

800

900

1000

1100

1200

pure Au

6.1 at %Sn

11.8 at% Sn

37.8 at% Sn

54.1 at% Sn

81.8 at% Sn

95.3 at% Sn

pure Sn

Temperature [K]

1273 1323 1373 1423 1473 1523

Sur

face

tens

ion

[mN

/m]

400

500

600

700

800

900

1000

1100

1200

pure Au

9.9 In at%

30.0 In at%

36.4 In at%

49.5 In at%54.9 In at%

88.7 In at%

pure In *

Experimental determination of the surface tension

Theoretical calculations of the surface tension

Experimental data are in good agreement with surface tension values calculated using different theoretical modelsExperimental data are in good agreement with surface tension values calculated using different theoretical models

Surface tensionSurface tension

Final Meeting COST Action 531 Vienna 17-18 May 2007

at%

Au

at%

Au

at%

Au

at%

Au

Au-InAu-InAu-InAu-In Au-SnAu-SnAu-SnAu-Sn

Experimental determination of the surface tension

Theoretical calculations of the surface tension

Experimental data are in good agreement with surface tension values calculated using different theoretical modelsExperimental data are in good agreement with surface tension values calculated using different theoretical models

Surface tensionSurface tension

Final Meeting COST Action 531 Vienna 17-18 May 2007

Temperature [K]

573 673 773 873

Su

rfa

ce T

en

sio

n [

mN

/m]

350

400

450

500

550

pure In95.0 at% In

85.0 at% In79.5 at% In

67.5 at% In

51.5 at% In

36.5 at% In30.0 at% In

15.5 at% In

5.0 at% Inpure Bi

at%

Inat%

In

In

Bi

at%

Inat%

In

Temperature [K]

600 650 700 750 800 850 900 950

Su

rfa

ce

te

ns

ion

[m

N/m

]

500

510

520

530

540

550

560

In 100

In 79.49

In 51.70

Sn 100

In 50.08

In 29.685

In 14.47

In 85.36

In 67.62

In 36.63

Bi-InBi-InBi-InBi-In In-SnIn-SnIn-SnIn-Sn

Temperature [K]

600 800 1000 1200 1400 1600

Su

rfa

ce

Te

ns

ion

[m

N/m

]

400

600

800

1000

1200

1400

Surface tensionSurface tensionCu-SnCu-SnCu-SnCu-Sn

at%

Cu

at%

Cu

Experimental determination of the surface tension

Theoretical calculations of the surface tension Final Meeting COST Action 531 Vienna 17-18 May 2007

at%

Cu

at%

Cu

Ag-CuAg-CuAg-CuAg-Cu

T=1373K

1 REG. SOL2 Prasad’smodel

□ □ Exp Results

Wetting ResultsWetting Results

Final Meeting COST Action 531 Vienna 17-18 May 2007

Wetting ResultsWetting Results

Final Meeting COST Action 531 Vienna 17-18 May 2007

Composition [at%]Composition [at%] Temperatures [K]Temperatures [K] SubstratesSubstrates

TTll TTff

NiNi CuCuff[°][°] ff [°] [°]

In-70SnIn-70Sn 450 710 20 41

In-85SnIn-85Sn 529 710 30 23

Au – 55 InAu – 55 In 768 852 50

Au – 97 InAu – 97 In 588 760 21

Au-82SnAu-82Sn 582 710 23 34

Cu-70SnCu-70Sn 813 910 26 <5

Cu-80SnCu-80Sn 743 910 25 <5

Cu – 90 SnCu – 90 Sn 653 910 10

Cu-95SnCu-95Sn 583 910 <5 <5

Bi – 52 InBi – 52 In 383 623 51Bi – 80 InBi – 80 In 355 648 44

Au – 5 In – 81 SnAu – 5 In – 81 Sn 538 645 33

Au – 11 In – 84 SnAu – 11 In – 84 Sn 493 600 52

Au – 8 In – 88 SnAu – 8 In – 88 Sn 503 602 23 39

Bi – 5 In – 81 Sn 483 608 39

Bi – 8 In – 88 Sn 430 608 30

60 m

In – 70SnIn – 70Sn

-Cu3Sn based phase

Ni substrateNi substrate

14 mNi3Sn4 based phase

-Cu6Sn5 based phase

Interface Characterization Interface Characterization

Final Meeting COST Action 531 Vienna 17-18 May 2007

Cu substrateCu substrate

As Pb-Sn solder alloys these systems showAs Pb-Sn solder alloys these systems show::

Formation of a layer (<100 m) of intermetallic compounds at the interface between solder alloys and substrate

These reactions are dominated by the Sn-component, but the and the -phase are exchanged

Similar behaviour:

•Cu-Sn/Ni•Au-In-Sn/Cu

CuCu

Au-55In

Final Meeting COST Action 531 Vienna 17-18 May 2007

Excessive dissolutive wetting

Similar behaviour:

•Cu-Sn/Cu

Interface Characterization Interface Characterization

Erosion of the substrate and Increase in the total volume

of liquid phase

Negative influence Negative influence on mechanical and on mechanical and

electrical properties electrical properties

Cu substrateCu substrate

Final Meeting COST Action 531 Vienna 17-18 May 2007

CuCu

BiIn2

Bi-52In

Interface macroscopically planar Similar behaviour:

•Au-Sn/(Cu,Ni)

•Bi-In-Sn/Cu

Interface Characterization Interface Characterization

Weakness of solder jointWeakness of solder joint

Cu substrateCu substrate

Final Meeting COST Action 531 Vienna 17-18 May 2007

ConclusionsConclusions

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 and 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 attentionThank for your attention