ThermodynamicsThermodynamics and and thermophysicalthermophysical propertiespropertiesofof liquidliquid BiBi--OO--SnSn alloysalloys

Donatella Giuranno, Enrica Ricci, Rada Novakovic, Elisabetta Arato

National Research Council Istitute for Energetics and Interphases

Via de Marini, 6 – 16149 Genoa, Italy

TOFA 2010 TOFA 2010 -- Discussion Meeting on Thermodynamics of Alloys Discussion Meeting on Thermodynamics of Alloys -- September 12September 12--16, 2010, Porto (Portugal)16, 2010, Porto (Portugal)

IntroductionIntroduction

MotivationMotivation

Bi–Sn alloys are regarded as one of the alternatives to toxic lead-containing solders, as made and as constituent of ternary alloys.

The surface properties and wetting characteristics of Bi-Sn, as otherslead-free solders, are presently subjected to very intensive studies.

The presence of oxides on the surface of solder alloys is of criticalimportance because it affects the formation of an otherwise goodsolder joint by degrading joint wettability and solderability.

Therefore, knowledge of surface oxidation and relatedmechanisms is a key issue in the optimisation of the welding

�Oxidation reactions under steady state conditions: evaporation of oxides and diffusion phenomena are takeninto account.

IdeaIdea

ToolsTools

TOFA 2010 TOFA 2010 -- Discussion Meeting on Thermodynamics of Alloys Discussion Meeting on Thermodynamics of Alloys -- September 12September 12--16, 2010, Porto (Portugal)16, 2010, Porto (Portugal)

mechanisms is a key issue in the optimisation of the weldingprocess.

into account.

�Surface tension as sensitive parameter to reveal oxidationprocesses undergoing at the liquid metal surfaces

�A fluid-dynamic model on the oxygen transport to evaluate:

� degree of contamination of the surface � mechanism of the gas mass-transfer at the liquid metal-

gas interface.

�Dynamic surface tension: influence of operative conditions (Temperature, Ptot, PO2, time).

ToolsTools

xKPPP sOx

sOO ∆+Κ+= '

22

*

Effective pressure

�Diffusion in gas phase under different regimes

Saturation pressure

O2

Oxide evaporation

Oxide

Mass transport in the liquid phase

Pure metals: The Effective Oxidation Pressure Pure metals: The Effective Oxidation Pressure

1,E+02

1,E+05

OxidationOxidation

E. Arato, E. Ricci, D. Giuranno, P. Costa, J. Cryst. Growth 293 (1) (2006)

under different regimes� Knudsen Ptot ≤ 1 Pa� Fick Ptot ≤ 105 Pa

�Oxidation phenomena:- predominant the most volatile oxide and the most stable oxide

� Reaction domains:- at gas-liquid interface - inside the gaseous layer

�Oxide condens/evapor�Metal condens/evapor

�Diffusion in liquid phase

The presence of volatile oxides can contribute to mantain the surface underoxygen-free conditions

sOxPΚ

1,E-25

1,E-22

1,E-19

1,E-16

1,E-13

1,E-10

1,E-07

1,E-04

1,E-01

1,E+02

600 650 700 750 800 850 900 950 1000

Temperature [K]

PO

2 [Pa]

sOP

2

xK ∆'

OxidationOxidation

sOxKP

TOFA 2010 TOFA 2010 -- Discussion Meeting on Thermodynamics of Alloys Discussion Meeting on Thermodynamics of Alloys -- September 12September 12--16, 2010, Porto (Portugal)16, 2010, Porto (Portugal)

� The imposed temperature is lowered / increased under well controlled PO2

(modulation of the temperature � modulation of the saturation level)

� Evidence of oxygen tensioactive effect ( “inversion points” ) from dynamicsurface tension measurements

By increasing and decreasing the temperaturefor several hours, “inversions” of the

540 1000

AA BBdγ/dT>0

Dynamic Surface Tension MeasurementsDynamic Surface Tension MeasurementsE. Ricci, E. Arato, A. Passerone, P. Costa, Adv. Colloid Interface Sci. 117 (1–3) (2005) 15.

for several hours, “inversions” of thetemperature coefficient are observed.

AA and BB points correspond respectively to the beginning and to the end of the oxygen tensioactive effect

→ the transition between oxidation and deoxidation regime occurs

500

510

520

530

0 1 2 3 4Time [h]

Su

rfac

e te

nsi

on

[m

N/m

]

500

600

700

800

900

Tem

per

atu

re [

K]

Surface Tension Temperature [K]

dγ/dT<0 dγ/dT<0

AA BB

TOFA 2010 TOFA 2010 -- Discussion Meeting on Thermodynamics of Alloys Discussion Meeting on Thermodynamics of Alloys -- September 12September 12--16, 2010, Porto (Portugal)16, 2010, Porto (Portugal)

Flow-meterHV

pump

GAS mixing chamber

Feed GAS

Exhausted gas

ASTRAview

Oxygen sensor “ PO outlet’’

CCD Light

SAMPLE

Oxygen sensor “ PO2 sample”

Oxygen sensor “ PO2 chamber’’

Thermocouple

Oxygen sensor “ PO2 outlet’’

Oxygen sensor “ PO2 inlet’’

Pt-heating elementStainless steel chamber

Alumina tube

TOFA 2010 TOFA 2010 -- Discussion Meeting on Thermodynamics of Alloys Discussion Meeting on Thermodynamics of Alloys -- September 12September 12--16, 2010, Porto (Portugal)16, 2010, Porto (Portugal)

Knudsen regime: Ptot ≤ 10-4 Pa

8 ▪10-7 Pa ≤ PO2 ≤ 1 ▪10-5 Pa

Dynamic Surface Tension Dynamic Surface Tension

L. Fiori, E. Ricci, E. Arato, Acta Mater. 51 (2003) 2873.

Effective Oxidation Pressure Effective Oxidation Pressure

O2 transport in liquid phase

PO2 eff

PO2 sat

TOFA 2010 TOFA 2010 -- Discussion Meeting on Thermodynamics of Alloys Discussion Meeting on Thermodynamics of Alloys -- September 12September 12--16, 2010, Porto (Portugal)16, 2010, Porto (Portugal)

Effective Effective OxidationOxidation Pressure: Pressure: PurePure metalsmetals

PO2 eff SnOSnSn isis the “the “lessless” ” oxidisableoxidisable

PO2sat SnO2

PO2sat Bi2O3

M1

O2

Oxide

M2

O2

Oxide

M1XM2Y

� Liquid phase = ideal solution

� Two possible evaporating and stable oxide species

Binary Alloys: The Effective Oxidation Pressure Binary Alloys: The Effective Oxidation Pressure E. Arato, E. Ricci, P. Costa, Surf. Sci. 602 (1) (2008) 349. E. Arato, E. Ricci, P. Costa, Surf. Sci. 602 (1) (2008) 349.

� Two possible evaporating and stable oxide species

� Ideal mixture of oxides

12 MMCs

Oxs

Ox PPf =Volatility ratio

12

22

MMAs

Os

O PPf =Oxidability ratio

),,/(2

212

*CAMiMjMiMiMM ffxxPPP s

Oxs

OO Φ+Κ+=−

TOFA 2010 TOFA 2010 -- Discussion Meeting on Thermodynamics of Alloys Discussion Meeting on Thermodynamics of Alloys -- September 12September 12--16, 2010, Porto (Portugal)16, 2010, Porto (Portugal)

),,/(2

212

*CAMiMjMiMiMM ffxxPPP s

Oxs

OO Φ+Κ+=−

212

*MMOP −

M121

2

*MMOP −

M1

Binary Alloys: The Effective Oxidation Pressure Binary Alloys: The Effective Oxidation Pressure

the behaviour of the alloy towards oxidation tends to be similar to the component

which forms the most volatile oxide (the “less oxidisable “)

the existence of at least a volatile oxide prevents the surface oxidation even if the

the behaviour of the alloy towards oxidation tends to be similar to the component

which forms the most volatile oxide (the “less oxidisable “)

the existence of at least a volatile oxide prevents the surface oxidation even if the

212

*MMOP −

M2

];min[ 2212121

221

2

***MMMMMMMM OOO PPP −−− =

the existence of at least a volatile oxide prevents the surface oxidation even if the

corresponding metal is present in low percentages.

the existence of at least a volatile oxide prevents the surface oxidation even if the

corresponding metal is present in low percentages.

BiBi--SnSn: : DynamicDynamic surfacesurface tensiontension measurementsmeasurements

TOFA 2010 TOFA 2010 -- Discussion Meeting on Thermodynamics of Alloys Discussion Meeting on Thermodynamics of Alloys -- September 12September 12--16, 2010, Porto (Portugal)16, 2010, Porto (Portugal)

EffectiveEffective OxidationOxidation PressurePressure

Bi30Sn70

Knudsen regime: Ptot ≤ 1 Pa

8 ▪10-14 Pa ≤ PO2 ≤ 2 ▪10-2 Pa

Bi43Sn57

Bi85Sn15

10-11 10-7 10-4 10-210-9

TOFA 2010 TOFA 2010 -- Discussion Meeting on Thermodynamics of Alloys Discussion Meeting on Thermodynamics of Alloys -- September 12September 12--16, 2010, Porto (Portugal)16, 2010, Porto (Portugal)

10-910-12 10-4

saturationBi O2 tensioactive effect

Bi: Bi: DynamicDynamic surfacesurface tensiontension measurementsmeasurements

EffectiveEffective OxidationOxidation PressurePressure ofof BiBi--OO--SnSn: T = 650 K: T = 650 K

PO Bi-O-Sn

),(),,/(2

212

*ji

sOx

sOO CAMiMjMiMiMM ffxxPPP ΨΨΨ+Φ+Κ+=−

Ψi =f(xsO2, Ps

ox,CL, transport coefficients, diffusivities)

PO2 eff Bi-O-Sn

PO2 sat Bi-O-Sn

ConclusionsConclusions�The experimental results obtained on the oxidation of Bi-Sn system in theliquid phase, agree very well with the predictions: the less oxidizable element(Sn) governs the behavior of the alloy towards oxidation.

�In many instances the existence of a volatile oxide (SnO) prevents thesurface oxidation even if the corresponding metal is present in low percentages:confirmed up to Bi95Sn5.

�If the evaporation of oxides from the surface is taken into consideration aswell as diffusion phenomena, the prediction of the real effective oxidationpressure is well comparable with experimental findings.

�Experimental and theoretical investigation of Bi-Sn oxidation tendencyunder Fick regime.

�Comparison between the results obtained by fluid-dynamic approach and theprediction of oxidation by applying thermodynamic models.

�Surface tension measurements and related temperature coefficients on Bi-Snliquid system under equilibrium conditions as a function of oxygen partialpressure.

Next stepsNext steps

TOFA 2010 TOFA 2010 -- Discussion Meeting on Thermodynamics of Alloys Discussion Meeting on Thermodynamics of Alloys -- September 12September 12--16, 2010, Porto (Portugal)16, 2010, Porto (Portugal)

Thank youfor your attention!for your attention!

TOFA 2010 TOFA 2010 -- Discussion Meeting on Thermodynamics of Alloys Discussion Meeting on Thermodynamics of Alloys -- September 12September 12--16, 2010, Porto (Portugal)16, 2010, Porto (Portugal)

EffectiveEffective OxidationOxidation PressurePressure ofof BiBi4343SnSn5757

T=T= 550550÷÷650 K650 K

Effective Oxidation Pressure of PbEffective Oxidation Pressure of Pb--OO--BiBi

390

410

430

450

470

Su

rfac

e te

nsi

on

[m

N/m

]

700

800

900

1000

Tem

per

atu

re [

K]

Fick regimeFick regimePPtottot = 10= 1055 PaPaPOPO22 ≅≅≅≅≅≅≅≅1010--22 PaPa

370

390

410

Su

rfac

e te

nsi

on

[m

N/m

]

800

900

1000

Tem

per

atu

re [

K]

400

420 1000

350

370

54 57 60 63 66 69 72

time [h]

Su

rfac

e te

nsi

on

[m

N/m

]

500

600

Surface Tension

T [K]

BiBi--95at%Pb95at%Pb

310

330

350

370

0 2 4 6 8 10 12 14 16 18

time [h]

Su

rfac

e te

nsi

on

[m

N/m

]

400

500

600

700

Tem

per

atu

re [

K]

Surface Tension

T [K]

BiBi--44.1at%Pb44.1at%Pb

300

320

340

360

380

400

0 5 10 15 20

time [h]

Su

rfac

e te

nsi

on

[m

N/m

]

500

600

700

800

900

Tem

per

atu

re [

K]

Surface Tension

T [K]BiBi--18at%Pb18at%Pb

Effective Oxidation Pressure of PbEffective Oxidation Pressure of Pb--OO--BiBi

1,E-07

1,E-05

1,E-03

1,E-01

1,E+01

[P

a]

PO Pb-O-Bi1,E-07

1,E-05

1,E-03

1,E-01

1,E+01

[P

a]

PO2 eff Pb-O-Bi

1,E-07

1,E-05

1,E-03

1,E-01

1,E+01

[P

a]

PO2 eff Pb-O-Bi

),(),,/(2

212

*ji

sOx

sOO CAMiMjMiMiMM ffxxPPP ΨΨΨ+Φ+Κ+=−

1,E-15

1,E-13

1,E-11

1,E-09

1,E-07

0,0 0,1 0,2 0,3 0,4 0,5 0,6 0,7 0,8 0,9 1,0

X Bi

PO

2 [P

a]

PO2 eff Pb-O-Bi

PO2 sat Pb-O-Bi

1,E-15

1,E-13

1,E-11

1,E-09

1,E-07

0,0 0,1 0,2 0,3 0,4 0,5 0,6 0,7 0,8 0,9 1,0

X Bi

PO

2 [P

a]

PO2 sat Pb-O-Bi

$

$ Hasouna et al. 1991

1,E-15

1,E-13

1,E-11

1,E-09

1,E-07

0,0 0,1 0,2 0,3 0,4 0,5 0,6 0,7 0,8 0,9 1,0

X Bi

PO

2 [P

a]

PO2 sat Pb-O-BiT = 762 K

500

510

520

530

540

550

0 2 4 6 8 10 12 14 16 18 20 22 24 26 28

Time [h]

Su

rfac

e T

ensi

on

[m

N/m

]

450

500

550

600

650

700

750

800

850

900

Tem

per

atu

re [

K]

In65Sn35

EffectiveEffective OxidationOxidation PressurePressure::

InIn--OO--SnSn

1,0E-15

1,0E-12

1,0E-09

1,0E-06

1,0E-03

1,0E+00

0 0,1 0,2 0,3 0,4 0,5 0,6 0,7 0,8 0,9 1

XSn

Pef

f [P

a]

In2O3 SnO2

In2O SnOIn-O-Sn

∆G In2O3 < ∆G SnO2

PS In2O > PS SnO

Volatility ratio ~ 102

Oxidizability ratio ~ 10-3

600 K

EffectiveEffective OxidationOxidation PressurePressure

CuCu--OO--SnSn

500

505

510

515

520

525

530

0 2 4 6 8 10 12 14 16 18 20 22

Time[h]

surf

ace

ten

sio

n[m

N/m

]

500

600

700

800

900

1000

Tem

per

atu

re[K

]

Cu5Sn95

∆G SnO2 < ∆G Cu2O

PS SnO > PS Cu2O> PS CuO

Volatility ratio ~ 107

Oxidizability ratio ~ 10-9

1.E-05

1.E-04

1.E-03

1.E-02

1.E-01

1.E+00

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0

XCu

PO

2 e

ff / P

a

Cu-O-Sn1050 K