Study of the Sn-Zn-X alloys for solder applicationsin the electronic industryWORKING TEAM IN GROUP PROJECT GP5:Portugal:Finland:Bulgaria:France:OBJECTIVE

The main objective of the project is the development of a new lead-free alloy for electronic application. The new alloy, based in the system Sn-Zn-X or Sn-Bi-X, will allow the substitution of the actual Pb-Sn solders. The specific objectives of the project are the selection of the alloying elements that allow the optimization of the properties with interest to the mentioned application. The new alloy must have properties similar to the actually used (melting point, ) in order to minimize the effects at the industry level. The samples used in this work were melted from pure elements (99.9 wt. %) in a resistance furnace under inert atmosphere (obtained by a constant flow of argon) and poured in a steel mold pre-heated up to 100 C. Two standard alloys were prepared for the sake of comparison with results obtained in the studied systems. The first alloy, a Sn-Pb base alloy, has a composition close to the actually used solder alloys in electronic soldering. The second alloy, of the Sn-Ag-Cu system, is an alternative alloy to the traditional solder alloys and to the compositions studied in this work.After melting and pouring, each alloy was heat treated using the following cycle: heating up to 120 C at 10 C/min, stage of 30 min and cooling to room temperature at 10 C/min.Fracture morphology of the different alloys a) and detail of the ductile and brittle fracture b) for, respectively, alloys 1 (0 wt.% Bi), 4 (3.3 wt.%Bi) and 6 (6.9 wt.%Bi). WORK PLANUniv. of Minho,Dep. Mechanical Eng.Physical Dep.Univ. of PortoMaterials Eng. Dep.Peixinhos, LdaHelsinki University of Technology,Department of Materials Science andRock Engineering Laboratory of Materials Processing andPowder Metallurgy University of Sofia,Faculty of Chemistry Universite Henri Poincare, Nancy 1Faculte des Sciences et TechniquesLaboratoire de Chimie du Solide Mineral, LCSM Groupe Thermodynamique et Corrosion Alloy synthesisUniv. of Minho - DEMAlloys characterisationThe microstructure of the alloy 1, of the system Sn-Zn-Al, reveals the presence of 3 constituents: matrix, a zinc rich phase, needles (black zone) and an aluminum rich phase (stars).For the smaller additions, bismuth forms a solid solution with the tin rich phase (fig. b).For higher additions of Bi, a separate phase, consisting essentially of Bi (white phase in fig. c), is formed.The solubility of Bi in the tin rich phase is higher, around 3.7 wt % in alloy 6, than the corresponding value for the binary Sn-Bi system (approximately 1 wt% at room temperature).Alloys microstructuresUniv. of Minho - DEMInfluence of Bi contents on the yield strength, ultimate tensile strength and elongation at rupture obtained in produced alloys.The effect of the Bi content on the Sn-Zn-Al-Bi system has been determined by tensile test experiments. It was concluded that Bi contents higher than ~5 wt% lowers the mechanical resistance and changes the fracture behavior from ductile to brittle.Mechanical propertiesUniv. of Minho - DEMMicrostructures obtained in the alloys, with different Bi contents: a) with 0%Bi; b) with 0.9 wt% Bi; c) with 6.9 wt% Bi (magnifications of 500X). Thermal propertiesUniv. of Minho - DEMThe transformation temperatures of the alloys has been determined by DSC/TGA. The experiments were made under inert atmosphere with a heating/cooling velocity of 10C/min.Melting temperature (or melting range) of alloys with different chemical compositions. Diffusion experimentsUniv. of Minho - DEMThe solder/substrate interface has been studied by diffusion experiments, between a solid substrate (pure copper) and the melted solder. Two stage times, at 250 C, were selected: 30 and 120 min. The layers obtained were studied by optical microscopy (OM) and scanning electronic microscopy (SEM/EDS).Several layers were detected for the Sn-Zn-Al and Sn-Zn-Al-Bi solders.Chemical composition of the phases and constituents, obtained by SEM/EDS, in alloys 1 and 6. Thermal and electric measurementsUniv. of Minho - DFSystems selectionUniv. of Minho, Univ. of Porto, Helsinki University of Technology, University of Sofia, Universite Henri Poincare

Two base alloy systems were selected considering the following aspects:

the melting temperature; the alloy final price.Thermal diffusivity measurements were performed by the photothermal beam deflection technique. In order to improve accuracy, independent measurements were performed under two different surrounding media, air and CCl4. Electrical resistivity measurements were performed by the four probe method.Thermall fatigue experimentsUniv. of Minho - DEMThe samples for thermal fatigue experiments have the following drawing:Copper

SolderSamples will be submitted to several thermal cycles (-40 to 120 C).After that the interface zone will analysed byptical microscopy and Scanning Electronic Microscopy. Cracks formation and evolution at the interface will be characterised in accordance with the thermal cycles for several solder chemical compositions.Chemical composition, obtained by XRF spectrometry, of the melted alloys

Work taskPartnersTime scheduleLiterature review1, 2, 3, 4, 5, 609-200212-2002Alloys synthesis1, 5, 601-200304-2003Microstructural characterization1, 2, 5, 604-200312-2004DSC and/or DTA experiments1, 2, 3, 509-200312-2004Melting and casting characterization1, 2, 509-200312-2004Mechanical characterization1, 501-200412-2004Literature search for thermodynamic and phase diagram data. Assessment of the data1, 2, 3, 501-200506-2005Determination of missing thermodynamic data1, 5, 609-200312-2004Choice of the models for the optimization procedure. Creation of thermodynamic database for the pertinent binary systems. Optimization of the ternary systems.2, 3, 506-200512-2006Industrial experiments1, 2, 310-200603-2007

SnAlZnBiPbAgCuNiLF190,50,888,30----LF389,00,648,21,78----LF585,31,129,13,9----LF681,41,079,57,6----LF1190,50,2480,87----LF1284,40,3586,9----LF1392,40,446,90,006----LF1490,90,545,52,69----LF1585,50,6585,4----LF16810,466,211,8----LF 1794,9--4,6--0,111-LF 1891,6--7,6--0,27-LF 1994,1--4,9-0,49-LF 2090,9--8,5--0,22-LF2189,8--8,9--0,77-LF 2293--5,6--0,8-LF2391,1--7,5--0,67-LF 2486,10,1089,83,33----LF 2589,4-6,53,11---0,2LF 2691,6-3,882,77---1,3P162,2--2,5634,7---P293,9----5,10,77-

Chart4

406332.5

46698.5

527721.3

538212.5

721007.5

71891.3

R 0,5

Rm

Elong. (%)

Bismuth content (Wt. %)

R0.5 and Rm (MPa)

Elongation (%)

Materiais_2003 (2)

AlloyHVR 0.2%Rm (MPa)AComposio qumicaComposio qumica sem BiGlobal CEMUP

% BiNAs-castHomog.(MPa)(MPa)(%)% Sn% Zn% Al% Bi% Sn% Zn% Al% Sn% Zn% Al% Bi

LF130.00612321406332.592.46.90.440.0066.920.4492.235.552.220

LF110.872242446698.590.580.240.878.100.2494.293.831.450.44

LF142.6933022527721.390.95.50.542.695.670.56

LF243.3342925538212.586.19.80.1083.3310.210.1194.913.550.291.24

LF155.453330721007.585.580.655.48.500.6993.32.012.022.68

LF126.96363471891.384.480.356.98.630.38

Pad171920405712.5

Pad2819161719

Bib_Pad127.230.648ref

Bib_Pad215 HBref

Sn-2,6Ag-0,8Cu-0,5Sb22.825.89ref

Sn-9Zn51.653.127ref

Materiais_2003 (2)

00

00

00

00

00

00

Bi content (wt. %)

Hardness (HV)

Materiais_2003_fases

000

000

000

000

000

000

R 0,5

Rm

Elong. (%)

Bismuth content (Wt. %)

R0.5 and Rm (MPa)

Elongation (%)

Durezas

00

00

00

00

00

00

ensaios de traco

AlloyMatrixAgulhasBismuto

% BiNmdiaZ0Z1

LF130.0061

LF110.872

LF142.693

LF243.334

LF155.45

LF126.96

Pad17

Pad28

Bib_Pad1

Bib_Pad2

Sn-2,6Ag-0,8Cu-0,5Sb

Sn-9Zn

Difuso

% BiBrutoHomogeneizadoPad1Pad2

LF 130.00622.6020.9019.3717.22

LF 110.8724.3023.9019.3717.22

LF 142.6930.1021.7319.3717.22Ensaios de Dureza

LF 155.432.5329.4619.3717.22

LF 126.935.8033.9019.3717.22

LF 1611.832.0830.5019.3717.22

Padro 119.1019.6419.37

Padro 218.9515.4917.22

Difuso

0000

0000

0000

0000

0000

0000

ligas bruto

ligas homogen.

padro 1

padro 2

% Bi

HV ( Kg/mm2)

HV vs % Bi

Folha2

Ensaios de Traco segundo a norma EN 10 002-1 1990

LigaRm (N/mm2)Rp .2%(N/mm2)Rp .5% (N/mm2)At %Observaes

P1 bruto61465121.5

P1 bruto62465016.3Partiu prximo de 1 das marcas de medida

P1 R58434523.8Parece ter 1 incluso ou rechupe na suprficie de fractura; Partiu bem

P1 L57404412.5Aparece um rechupe de maior dimenso no meio da superfcie de fractura ; partiu fora da zona

P2 R382326Apresenta rechupes exteriores ,partindo desse lado, fora da zona

P2 L191719Apresenta rechupes exteriores ,partindo fora da zona. No deu para medir o Lf

LF 11 L6946528.5Aparece um poro grande superficialmente e outros mais pequenos; Apresenta um grande buraco de gs interno

LF 11 R744754No aparecem poros superficiais mas aparece um grande buraco interno;Partiu em cima da marca

LF 12 L8971781.3Muito frgil, quase no tem deformao; Aparece um rechupe e poro.

LF 12 R11171824.0Material frgil com pequeno rechupe lateral; Partiu em cima da marca

LF 13 L63404832.5Apresenta rechupe interior

LF 13 R64384431.3Aparecem deformaes exteriores

LF 14 L77525821.3Apresenta um pequeno rechupe interior na superficie de fractura; Partiu fora das marcas

LF 14 R57485515.0Apresenta um pequeno rechupe interior na superficie de fractura;Parte da fractura est fora das marcas

LF 15 L108Rt = 11Rt = 9312.5Ensaio sem extensmetro ; Pequeno rechupe

Lf 15 R10072807.5Apresenta rechupe na superficie de fractura

LigaRm (N/mm2)Rp .2%(N/mm2)Rp .5% (N/mm2)At %

% Bi

0.006LF 13 L63404832.5

0.87LF 11 L6946528.5

2.69LF 14 L77525821.3

5.4LF 15 R10072807.5

6.9LF 12 L8971781.3

P1 LP1 L57404412.5

P2LP2 L191719

Folha2

0000

0000

0000

0000

0000

Rm vs %Bi

Rp.2% vs % Bi

Rp.5% vs %Bi

At % vs % Bi

%Bi

Rm/Rp/At

Folha3

LF 3-iso1 ( 250C, 30` )Ensaios de Difuso

AgulhaSoldaZ1Z2Z3Cobre

12345

Al0.970.0919.5314.322.870LF3 -iso1- (250 C , 30`) (1,78 % Bi)

Zn98.694.6613.0615.4425.10

Sn0.3392.2625.213.470.870

Bi01.640.4800.250

Cu01.3541.7266.7770.9100

LF 6-iso1 ( 250C , 120` )

Z1 (Solda)Z2Z3Z4Z5Z6Cobre

123457

Al0.231.0223.9315.850.180

Zn4.878.258.3412.0500

Sn83.573.232.811.610.270

Bi10.060.80.740.3100

Cu1.1256.764.1870.1899.54100

Folha3

0.094.6692.261.641.35

19.5313.0625.210.4841.72

14.3215.443.47066.77

2.8725.10.870.2570.9

0000100

Solda

Cobre

% Al

% Zn

% Sn

% Bi

% Cu

zona de difuso

% elemento

00000

00000

00000

00000

00000

00000

Solda

Cobre

% Al

% Zn

% Sn

% Bi

% Cu

zona de difuso

% elemento

LF 6-iso1 ( 250C , 120`) (7,6 % Bi)

1 4 6

Alloy N

Zone

% Sn

% Zn

% Al

% Bi

Z1

1.5

26.6

71.9

-

1

Z2

95.4

4.4

0.2

-

Z3

1.0

98.5

0.5

-

Z1

4.0

31.4

64.1

0.5

Z2

92.2

3.9

0.2

3.7

6

Z3

1.0

98.5

0.5

-

Z4

1.9

1.6

-

96.5

Sample

% Bi

Melting temperature (C)

LF22

5.6

~186 - 220

LF23

7.5

~202 225

LF21

8.9

138; ~178 216

LF19

4.9

188 - 221

Sample

% Bi

Melting temperature (C)

Sn

0

231.7

P1

2.5

174.0

P2

-

215 - 220

LF1

0

198.7

LF3

1.8

197.3

LF5

3.9

188.5

LF6

7.6

~162 189

a) Sn-Zn-Al alloy

b) Sn-Zn-Al-Bi alloy with7.6 wt.% Bi

_1110388542.doc

_1110388596.doc

Sample

Thermal

Diffusivity

air/ 10-5 (m2/s)

Thermal Diffusivity

CCl4 / 10-5 (m2/s)

Electrical resistivity

/ ((.(.cm)

Thermal Diffusivity

(literature values)

(10-5

m2/s)

Sn

4.61

4.01

23.94

Sn 4.1

P1

3.27

3.02

15.76

Bi 0.94

P2

4.57

4.02

11.51

Cu 12

LF12

3.25

-

-

Pb 2.4

LF13

4.07

-

16.57

Zn 4.6

LF16

3.12

3.06

16.32

Ag 17

LF23

3.14

-

-

Al 9.8