2014 Solder Joint Reliability

8/10/2019 2014 Solder Joint Reliability

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15.0 Release

Hari SubramaniamTechnical Services Engineer

ANSYS, Irvine, [email protected]

Solder Joint Reliability (SJR) underThermal Cycling


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1-2ANSYS, Inc. Proprietary

2009 ANSYS, Inc. All rights reserved.February 23, 2009Inventory #002593

2011 ANSYS, Inc. October 8, 20142

Solder Joint Failure

CTE mismatchAt Elevated Temperature

Low CTE

High CTE

Undeformed state

Stiffness mismatch


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For most consumer electronics, thermal cycling is the main cause for fatigue Plasticity and Creep causes solder joints in electronics to undergo incremental

damage with every thermal cycle Each load cycle causes stress damage to solder Damage accumulates over time

Damage Accumulation


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Fracture is typically not modeled explicitly for SJR since this would becomputationally expensive

Instead, crack size or life are related to other parameters such as plastic work orstrain

By having ANSYS calculate plastic strain or work, we can relate this to the life ofthe part

Life Prediction


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Utilize constitutive material model Possible inclusion of inelastic, rate-dependent and

temperature-dependent effects ANAND, Creep Models

Volume-averaged approach Pick a region and determine a volume-averaged

quantity for Life calculation

Predict Life Darveaux, Syed

Solder Joint Reliability - Workflow

Possible failure regions. VolumeAveraging done within this toPredict TTF


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Plasticity models describe inelastic behavior that develops when the stress levelgoes beyond the yield strength of the material

Usually, a type of kinematic hardening is suitable for cyclic loading behavior Can be rate-independent or rate-dependent or coupled with creep

Review of Plasticity

Yield Strength y

Elastic Plastic

Unloading


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Creep strain is driven by stress and temperature without a distinct yield surface. Usually separated into three regions Primary, Secondary, Tertiary. Solder

joint reliability is typically interested in secondary creep effects to get stabilizedcycles

Review of Creep

Generalized Garofalo (Hyperbolic Sine)

Combined Time Hardening (Double Power Law)

( )[ ] 34

21 sinh C T C

cr C eC

=&

( ) /T C C

/T C C C

cr te C C

et C

76

432

5

3

1

1

1

+

++

=


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Popularized by Darveaux and others forsolder joint simulations

ANAND Model can be thought of as aspecial form of hyperbolic sine law with an

evolution term s

Review of ANAND Model

R. Darveaux, Effect of Simulation Methodology on Solder Joint CrackGrowth Correlation, ECTC 2000

m RT

Q

ins

Ae

1

sinh

= &


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Inelastic Strain (or sometimes referred to as creep strain or plastic strain) is theirrecoverable strain that develops

Accumulated inelastic strain is an always increasing quantity Plastic Work (or creep strain energy) is the energy associated with this inelastic

strain

Volume Averaging technique will be used to reduce the sensitivity to meshing Plastic Work

Plastic Work and Strain

Possible failure regions. VolumeAveraging done within this toPredict TTF

=

V

V W W avg

volumeunit per work PlasticW ....=


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Model proposed by Syed et al

Model proposed by Darveaux et al

Crack Initiation

Crack Growth

Characteristic Life

Life Prediction Methods

( ) 1= acc f W N

( ) 1= acc f C N

2

10K

avgW K N =

4

3K

avgW K dN da =

dN da

a N W += 0

Nf Cycles to FailureC and W Material Parameterseacc Accumulated creep strain per cyclewacc Accumulated creep energy density per cycle

Here, K 1 through K 4 are material

parametersa is the joint diameter at the interface(final crack length)

W is the plastic work per cycle


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Geometry Split the solder region for Volumetric Averaging Use DesignModeler, Spaceclaim

Workflow - Geometry


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Input Material properties in the Engineering Data

Workflow Material Data


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Check Connections Contact Create Named Selection

Named Selection will be used during post-processingfor calculating the volume averaged plastic work

Apply Thermal condition up to 3 to 4 cycles

Workflow - Loading


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Workflow - Postprocessing APDL Commands are used for volumetric

averaging and Life calculations


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NL-PLWK can be plotted using User-Defined Results

Workflow - Postprocessing


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ANSYS also provides other approaches for failure prediction Cohesive Zone Model (CZM) Fracture Parameter

J-Integral Calculations [J]

Stress Intensity Factor [K] Energy Release Rate [G]

Crack Growth VCCT based crack growth

APPENDIX Other Methodologies


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ANSYS nCode DesignLife

PSD Cycle Counters

NarrowBand Only suitable for signals with single frequency content Steinberg Electronics Dirlik First general purpose (wideband) technique LaLanne Military Standard

APPENDIX Other Methodolgies


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Q & A

Thank you

Hari [email protected]

2014 Solder Joint Reliability

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