Venkatesh Sivasubramaniam - COST 531 Final Meeting, Vienna,17-05-2007 1 Particle reinforced...

Venkatesh Sivasubramaniam - COST 531 Final Meeting, Vienna,17-05-2007

1

Particle reinforced lead-free solders

A Comparative study on reinforcing Sn-4Ag-0.5Cu solder with

nano and micron sized Cu particles

V.Sivasubramaniam1, 2, J.Janczak-Rusch1, J.Botsis2, J.Cugnoni2

1-Laboratory of Joining and Interface Technology, EMPA Material Science and Technology, Dübendorf, Switzerland

2-Laboratory of Applied Mechanics and Reliability, EPFL, Lausanne, Switzerland

COST 531 Final Meeting, Vienna,17-05-2007


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Overview

Motivation - Composite solders

Materials and processing method

Microstructural analysis of particle reinforced solders

Mechanical properties of solder joints

Failure analysis- Fractography

Conclusion and Future Work


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Motivation-Composite approach

Controlling the growth and formation of intermetallics at the interface (eg. Cu/solder) – during higher service temperature

Source:Szu-Tsung Kao et. al , J.Electron. Materials,Vol.35,No.3 (2006)


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Materials used-Current work

Matrix alloy Sn-4Ag-0.5Cu (supplied by Alpha metals)

Base metal - Standard Cu

Reinforcement particles

Cu particles 3-20μm Cu2O nano particle 150nm


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Synthesis and Characterization of nano Cu2O particles

Cu(NO3)2

[232.59] [143.08]

160°C; ArN O

[111.14]

495HO

OH

Cu2O6 + 2.5 x H2O2

Chemical reduction route (literature source…)

Cu2O


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Specimen preparation

Manual Mixing of particles with SAC405 paste using mortar

Initially (melt) samples were made in circular (AlN) crucible for microstructural analysis

Mortar


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Microstructural analysis- SAC405+2 wt% micro Cu

0

10

20

30

40

50

60

70

80

90

100

0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32

Distance in microns

wt%

Sn L

Cu K


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Microstructural analysis- SAC405+2 wt% nano Cu2O

0

10

20

30

40

50

60

70

80

90

100

0 2 4 6 8 10 12

Distance in microns

wt.

%

SnL

CuK

All of the Cu2O has been converted in to CuSn IMC!


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Quality control of joints-X-ray Radiography

Step gage from SAC405 cast

width of tensile specimen joint


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Mechanical Characterization-Reproducibility


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Mechanical Characterization-Results


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Fractography results of tested composite solder joints

micro Cu nano Cu

cup and cone

ductile fracture!


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Mechanical characterization-Aged composite solder joint

Dotted curves –Aged joints isothermally for 24hrs @ 130°C


14

Interfacial IMC of composite solder joint

SAC405+2wt% micron-Cu

before ageing after ageing

20µ

20µ20µ


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Microstructural analysis of composite solder joint ‘after’ ageing

SAC405+2wt% Nano Cu SAC405+2wt% micron Cu

No appreciable interfacial layer growth for solders with Nano Cu

Cu core was evident even after ageing for samples reinforced with

micron Cu


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Conslusions

Composite solder prepared with nanometer scale Cu particles are expected to

have better creep properties (higher strain rates are achievable)

Potential solution for microelectronics interconnects where good tensile and

plastic properties are required

Growth control of interfacial layer for joints made with nanoscale Cu is evident

Mechanism of increase in strain rate for joints with nanoscale Cu

reinforcement must still explained

Future Work

Creep tests for Composite solders

Ageing for longer duration


17

Extra slides


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Composite solder joints-Tensile test specimen preparation

Tensile test specimen-0.5mm gap width

0.5mm gap width, 2wt% reinforcement with microCu and ultrafineCu2O

4 specimens per batch

Test conditions:

Tensile test-Instron Microtester 5848-cross head speed of 0.5µ/sec

Digital image Correlation (DIC) technique developed by Dr. J.Cugnoni

DIC setup for localized strain field measurement


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Mechanical Characterization-Microhardness (load:200gms,30sec)

12.0

13.0

14.0

15.0

16.0

17.0

18.0

19.0

20.0

Vic

kers

har

dn

ess

(HV

)

SAC 4052wt% ultra fine Cu2O

2wt% micro Cu

2wt% micro Ni


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Stress-strain curve- 0.5mm- 2wt% ultra fine Cu2O

0

10000000

20000000

30000000

40000000

50000000

60000000

0% 5% 10% 15% 20% 25% 30% 35% 40% 45% 50%

strain

stre

ss(P

a)

(RT)


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Influence of particle reinforcement on the mechanical behaviour

0

10

20

30

40

50

60

70

80

0 0.0005 0.001 0.0015 0.002 0.0025 0.003 0.0035 0.004Strain (-) [gage length=50 mm]

Str

ess

(MP

a)

"Sn-4Ag-0.5Cu @ 234degC,without vacuum"

"Sn-4Ag-0.5Cu,Ni part. 5%wt. @ 234degC,with vacuum"

"Sn-4Ag-0.5Cu,Cu part. 5%wt. @ 234degC,with vacuum"


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Results from previous tests (old temp. profile)


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• The driving force of the moving of the Cu from substrate is due to the concentration difference in solders and substrate

• Ni and Cu have similar chemical characteristics,thus their diffusion in Sn is expected to be similar but due to the simultaneus presence of Cu,Ni in Ni reinforced Sn3.5Ag which apparently accelerates formation of (Cu-Ni-Sn) IMC

• However since there is not much growth of interfacial layer in Ni reinforced Sn3.5Ag below 100C its quite suitable for applications such as computers where the service conditions are below 100C

• Cu6Sn5 particles inhibits the growth of interfacial IMC by increasing the activation energy from 0.8eV to 1.23eV in SnPb

• It appears that creep resistance FeSn2 > Ni3Sn4 > Cu6Sn5 > Eutectic SnAg

Literature review - Consolidated inferences


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Microstructural analysis of composite solder joint ‘before’ ageing

SAC405+2wt% ultra fine Cu2O

SAC405+2wt% micron-Cu

10microns

10microns


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Microstructural analysis of composite solder joint ‘after’ ageing

SAC405+2wt% nano Cu SAC405+2wt% micron-Cu


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nano Cu2O particles

Disperse in SAC405 paste

Strong flux(OM338)

Reflowed at 240°C

SAC405 reinforced with CuSn(IMC)

Cu2O Cu


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29


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Quality control of joints-X-ray Radiography

Step gage from SAC405 cast X-ray image of step gage

Venkatesh Sivasubramaniam - COST 531 Final Meeting, Vienna,17-05-2007 1 Particle reinforced...

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Transcript of Venkatesh Sivasubramaniam - COST 531 Final Meeting, Vienna,17-05-2007 1 Particle reinforced...