Characterization of 1mm lead-free joints

Test results (DIC 2D)Measured stress-strain curves (DIC)

0.00E+00

1.00E+07

2.00E+07

3.00E+07

4.00E+07

5.00E+07

6.00E+07

0 0.005 0.01 0.015 0.02 0.025 0.03

1A

1B

1C

2A

2B

2C

3A

3B

3C

4A

4B

4C

2

31

4

Experimental results Measured stress-strain curves:

Improved resolution/noise with 2D DIC: Displacement +/-0.2 microns, strain +/- 2E-4 Correction of the out of plane displacement effects

Apparent properties and variability:

Plate Apparent yield stress var +/- Ultimate stress var +/- Hardening var +/-1 22.8 6.6% 43.0 5.8% 20.2 11.2%2 32.7 7.7% 52.8 4.7% 20.1 4.2%3 29.0 5.2% 46.7 2.7% 17.7 15.6%4 35.2 2.8% 49.3 6.4% 14.1 15.2%

Overall 29.9 25.1% 47.9 15.3% 18.0 27.5%

Large variability between plates, lower variability for a given plate

effects of processing parameters / microstructure ?

Plasticity - damage evolution (1B)Stress-strain curve 1B

0.00E+00

5.00E+06

1.00E+07

1.50E+07

2.00E+07

2.50E+07

3.00E+07

3.50E+07

4.00E+07

4.50E+07

5.00E+07

0 0.002 0.004 0.006 0.008 0.01 0.012 0.014

strain

stre

ss

Plasticity - damage evolution (2B)Stress-strain curve 2B

0.00E+00

1.00E+07

2.00E+07

3.00E+07

4.00E+07

5.00E+07

6.00E+07

0 0.001 0.002 0.003 0.004 0.005 0.006

strain

stre

ss

Plasticity - damage evolution (3A)Stress-strain curve 3A

0.00E+00

5.00E+06

1.00E+07

1.50E+07

2.00E+07

2.50E+07

3.00E+07

3.50E+07

4.00E+07

4.50E+07

5.00E+07

0 0.005 0.01 0.015 0.02 0.025 0.03

strain

stre

ss

Plasticity - damage evolution (4A)Stress-strain curve 4A

0.00E+00

5.00E+06

1.00E+07

1.50E+07

2.00E+07

2.50E+07

3.00E+07

3.50E+07

4.00E+07

4.50E+07

5.00E+07

-0.002 0 0.002 0.004 0.006 0.008 0.01 0.012 0.014 0.016

strain

stre

ss

Plasticity - Damage evolution: remarks Need to distinguish two phenomena:

Elasto-plastic deformation: global behavior of the solder joint Failure : local behavior, depends on the interfacial properties

Evolution during testing: Plasticity is “homogeneous” up to 90% load at least => most of

the stress-strain curve can be used for characterization Failure in the last 15 seconds of the test:

concentration of deformations in a corner & on the interface crack propagation: 1 crack on each interface (A), 1 single crack (B)

A B

Characterization: 3D FE modelling

Inside

Outside

3D model: better accuracy & numerical stability,but resolution time x 2.

Average Strain: 2%Max Strain: 10%

Plasticity evolution

Stress-strain curve 1B

0.00E+00

5.00E+06

1.00E+07

1.50E+07

2.00E+07

2.50E+07

3.00E+07

3.50E+07

4.00E+07

4.50E+07

5.00E+07

0 0.002 0.004 0.006 0.008 0.01 0.012 0.014

strain

stre

ss

Characterization: identification

~1h / 40 FE solutions to identify the material properties, parameters: E, yield stress, hardening, exp. Hardening rateAccuracy: max error +/-4% !!

Identification results: constraining effects1B 2A

3A

0.00E+00

1.00E+07

2.00E+07

3.00E+07

4.00E+07

5.00E+07

6.00E+07

0 0.005 0.01 0.015 0.02 0.025

Constrained

Unconstrained

0.00E+00

1.00E+07

2.00E+07

3.00E+07

4.00E+07

5.00E+07

6.00E+07

0 0.005 0.01 0.015 0.02 0.025

Constrained

Unconstrained

0.00E+00

1.00E+07

2.00E+07

3.00E+07

4.00E+07

5.00E+07

6.00E+07

0 0.005 0.01 0.015 0.02 0.025

Constrained

Unconstrained

0.00E+00

1.00E+07

2.00E+07

3.00E+07

4.00E+07

5.00E+07

6.00E+07

0 0.005 0.01 0.015 0.02 0.025

Constrained

Unconstrained

4B

Constitutive stress-strain curvesConstitutive Stress Strain curves

0.00E+00

5.00E+06

1.00E+07

1.50E+07

2.00E+07

2.50E+07

3.00E+07

3.50E+07

4.00E+07

4.50E+07

5.00E+07

0 0.005 0.01 0.015 0.02 0.025

Strain

Str

es

s

1B

2A

2B

3A

3B

Next steps Testing:

0.5 mm & 0.2 mm joints Reinforced solder joints Split testing in 2 procedures:

A simple one to compare materials A complete test for characterization

Developpments Bulk solder specimen (FEM =>Design =>production) A better test specimen for joints ?

Shear test (Nokia)? Tensile test ?