best practices fea modeling - dfr solutions
TRANSCRIPT
Best Practices FEA Modeling
March 9, 2016
© 2004 - 2007© 2004 - 20109000 Virginia Manor Rd Ste 290, Beltsville MD 20705 | 301-474-0607 | www.dfrsolutions.com
o Manoj Chinnakonda – Technology Solutions Consultant in the SIMULIA Industry Diversification team
Manoj Chinnakonda develops technical workflows in the Flexible Electronics domain that highlight values and applications of key technologies and products within the SIMULIA ecosystem. Prior to taking up this role, Manoj worked as a technical specialist promoting SIMULIA solutions for Life Sciences and Automotive industries. Manojjoined SIMULIA in Nov 2007 and holds a Master's degree in Mechanical Engineering from Clemson University, SC.
o Nathan Blattau, Ph.D. – DfR Solutions, Senior Vice PresidentHas been involved in the packaging and reliability of electronic equipment for more than ten years. His specialties include best practices in design for reliability, robustness of Pb-free, failure analysis, accelerated test plan development, finite element analysis, solder joint reliability, fracture, and fatigue mechanics of materials.
© 2004 - 2007© 2004 - 20109000 Virginia Manor Rd Ste 290, Beltsville MD 20705 | 301-474-0607 | www.dfrsolutions.com
DfR Solutions
The Industry Leader in
Quality-Reliability-Durability
of Electronics
50 Fastest Growing Companies in the
Electronics Industry
- Inc Magazine
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DASSAULT SYSTÈMES
a ScientificcompanyCombining Science,
Technology and Art for a
sustainable society
14,000passionate people• 123 nationalities / 172 sites
• One global R&D / 56 labs
• Game changing 3DEXPERIENCE
solutions
>200,000 enterprise customers• 12 industries in 140 countries• 25 million users
12,600partners• Software, Technology &
Architecture
• Content & Online Services
• Sales
• Consulting & System
Integrators
• Education
• Research
Long-termdriven• Majority shareholder control
• Revenue: $3.2 Bn*
• Operating margin: 30.8%*
* Figures as of FY 2015 / Non-IFRS
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What is SIMULIA and Realistic Simulation?
• SIMULIA is the Dassault Systèmes brand for Realistic Simulation“Predictive Crashworthiness Simulation in a Virtual Design Process without Hardware Testing”, Jurgen Lescheticky, Hariaokto Hooputra and Doris Ruckdeschel, BMW Group, SIMULIA Customer Conference, May 2010
Courtesy Mechanical Design and Analysis Corporation, 2010 SCC
Statistical distribution of impact damageCourtesy of University of Zagreb, 2010 SCC
Courtesy of BMW Group, 2010 SCC
© 2004 - 2007© 2004 - 20109000 Virginia Manor Rd Ste 290, Beltsville MD 20705 | 301-474-0607 | www.dfrsolutions.com
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Finite Element Method
o Numerical method originally developed to solve solid
mechanics problems (mostly for aerospace)
o Used for solving complex problems where analytical
solutions are not possible
o Analytical Solution
o Stress analysis of beams
o Finite Element Model
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Drop Testing
Fracture &
Failure
Structural Load Cases
FOR
HIGH-TECH
RELIABILITY
© 2004 - 2007© 2004 - 20109000 Virginia Manor Rd Ste 290, Beltsville MD 20705 | 301-474-0607 | www.dfrsolutions.com
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Finite Element Modeling
o Some Common uses for FEA in the electronics industry
o Static loading (force/displacement)
o Dynamic
o Vibration response
o Shock response
o Thermal mechanical fatigue
o Solder fatigue
o Copper fatigue
o Thermal mechanical response (thermal analysis)
o Electromagnetic Simulation
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ChallengeReduce weight of the product without loss of
structural strength or rigidity
SolutionSIMULIA Abaqus technology to assess the strength of
CFRP based frame designs
Benefits“With Abaqus, we're able to be more innovative,
more quickly, and produce higher-quality
products.”—Dr. Zhifeng Xin, LenovoImages Courtesy of Lenovo
Static Loading
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Images Courtesy of Xerox
ChallengeDesign a low-cost printer chassis that can withstand a
series of transportation drop tests
SolutionDrop testing using SIMULIA Abaqus technology used
to optimize 3 structural members for size and material
grade
BenefitsAdditional savings of $3.50 (5%) in an already
“optimized” design. Optimized structural members
absorb about 19% more energy whilst reducing the
load transferred to the castors by about 8%
Drop Testing/Mechanical Shock
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Challenge• Low-cycle fatigue is a common failure mechanism of
solder joints in electronic packaging
• Predict the critical location of ball grid array (BGA)
undergoing low-cycle fatigue and the fatigue life of the
critical solder joints
Solution• Direct Cyclic procedure in Abaqus/Standard to
simulate the thermal cycling of the BGA package
• Submodeling of the critical region to assess
fatigue life of critical solder joints
BenefitsDirect cyclic procedure combined with submodeling
was used to efficiently and precisely predict the failure
location on the ball
Thermal Cycling Fatigue
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ChallengeEvaluate the reliability of though-silicon via (TSV)
interposers and interconnects in newly designed
packages
SolutionUsed thermo-mechanical simulations in Abaqus to
understand the impact of moisture and temperature
cycling on the μbumps and adhesion of the underfill to
the top FPGA die and thin TSV interposer substrate
BenefitsSeveral DOEs were performed to maximize yield and
reliability. The Si interposer yielded a reliable package with
acceptable warpage/coplanarity, passing 1000TCB without
any crack, delamination, or void in low-k, TSV, μbumps, and
C4 bumps
Thermal Mechanical
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“The combination of Dassault
Systèmes’ 3DEXPERIENCE
platform with CST STUDIO SUITE
technology will enable customers to
create and analyze electromagnetic
behavioral models that simulate
device function in a wide range of
frequencies. This capability
enhances the 3DEXPERIENCE
platform’s simulation applications for
solving multi-physics challenges in
several areas including hybrid
vehicle drivetrains and wearable
electronics.”
Electromagnetic
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Co-Design with Dassault Systèmes and CST Solutions
Smartband
Structural and EM design in the
3DExperience platform for
integrated, multi-disciplinary
Optimization
Flex Cables
Sequential Structural and EM
solution with easy import and
export of results.
Smart Appliances
Tightly coupled Structural and
EM analysis.
Co-Simulation framework
Collaborative Design Integrated MultiphysicsConcurrent Design
© 2004 - 2007© 2004 - 20109000 Virginia Manor Rd Ste 290, Beltsville MD 20705 | 301-474-0607 | www.dfrsolutions.com
o Finite elements are entities that connected to each other
through nodes
o Material information determines how the loads applied to
nodes are transferred into displacements for all the connected
nodes
o FEM is a displacement analysis {F}=[K]{x}
o Nodes – coordinate locations and are where loads are
applied.
o Elements – material properties and equations that
determine loads and stresses based on nodal
displacements
Aspects of a Finite Element Model
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© 2004 - 2007© 2004 - 20109000 Virginia Manor Rd Ste 290, Beltsville MD 20705 | 301-474-0607 | www.dfrsolutions.com
o Create the parts (geometry)
o Define and assign materials
properties
o Assemble the parts
o If parts are bonded together they
can be merged
o If parts may interact with each then
that needs to be defined
o The interactions depend on the type
of analysis being performed
o Define the type of analysis (step)
o Define interactions
o Define loads
o Generate the mesh
o Run the analysis
o Post process the results
Work Flow
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Geometry Generation
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© 2004 - 2007© 2004 - 20109000 Virginia Manor Rd Ste 290, Beltsville MD 20705 | 301-474-0607 | www.dfrsolutions.com
o Sherlock software automatically performs the material assignment and
the assembling of the parts
o In this case we need to make a part to bend the flex circuit
o Refine material properties
Geometry
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© 2004 - 2007© 2004 - 20109000 Virginia Manor Rd Ste 290, Beltsville MD 20705 | 301-474-0607 | www.dfrsolutions.com19
Geometry - Axisymmetric Modeling
o Circular 3D
geometries can be
reduced to 2D model
use axisymmetric
o Plated Through Holes
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Via in Pad Plated Over (ViPO)
© 2004 - 2007© 2004 - 20109000 Virginia Manor Rd Ste 290, Beltsville MD 20705 | 301-474-0607 | www.dfrsolutions.com
o Geometry created by 3D modeling tools are rarely
good for finite element modeling
o May contain slivers
o Free edges
o Very small faces
o Redundant vertices
o The geometry will need to be
“cleaned up” prior to meshing
o All these features will be forced into the mesh and will
cause very large model sizes and meshing problems
o There are tools inside Abaqus to aid in the removal of
such features
Importing Geometry
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© 2004 - 2007© 2004 - 20109000 Virginia Manor Rd Ste 290, Beltsville MD 20705 | 301-474-0607 | www.dfrsolutions.com
o Have Abaqus to ignore
certain features
Example: Virtual Topology
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© 2004 - 2007© 2004 - 20109000 Virginia Manor Rd Ste 290, Beltsville MD 20705 | 301-474-0607 | www.dfrsolutions.com
o It is important to use the correct units for the material
properties
o Depends on the length units of your geometry
o Always double check
o Most FEA are unitless
It up to the user to
make sure values
are entered properly
Material Properties - Units
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© 2004 - 2007© 2004 - 20109000 Virginia Manor Rd Ste 290, Beltsville MD 20705 | 301-474-0607 | www.dfrsolutions.com
o The material properties need to fit the type of analysis
you plan to conduct
o Example:
o One time bend of a flex circuit to simulate assembly process
o Is the copper going to break
o Copper plasticity needs to be
defined
o *Deformation Plasticity
o Ramberg-Osgood formulation
Material Properties
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Assembly
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© 2004 - 2007© 2004 - 20109000 Virginia Manor Rd Ste 290, Beltsville MD 20705 | 301-474-0607 | www.dfrsolutions.com
o Things to consider
o Symmetry, allows for model
size reduction
o Three dimensional elements
don’t have rotational
degrees of freedom, rotation
is constrained by putting
displacement boundary
conditions on multiple nodes
o In this example there are
analytical surfaces that do
have rotational degrees of
freedom
Boundary Conditions
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Bending of Flex
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Copper Plasticity
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o The quality and size of the elements influences the
results
o Best practice is to conduct a mesh convergence study
o Used to determine the optimal element size for the boards
you are modeling
o Limiting factors: time, memory and how good is good enough
o Example:
o Natural frequency
Mesh Quality
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© 2004 - 2007© 2004 - 20109000 Virginia Manor Rd Ste 290, Beltsville MD 20705 | 301-474-0607 | www.dfrsolutions.com
o The more uniform the
mesh the better
o The goal is to have a
mesh that gives the
most accurate answer
without having an
excessive number of
elements
o Mesh convergence,
decrease the mesh size
until the answer doesn’t
change or changes very
little
o Simple plate example
Mesh Quality and Convergence
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Element size 15 mm
© 2004 - 2007© 2004 - 20109000 Virginia Manor Rd Ste 290, Beltsville MD 20705 | 301-474-0607 | www.dfrsolutions.com30
Natural Frequency, 15 mm Mesh
o Using many large elements increases the stiffness of the model
o Natural Frequencies
o 192 Hz
o 353
o 515
o 669
o 826
o 907
o Run time 22.7 seconds
© 2004 - 2007© 2004 - 20109000 Virginia Manor Rd Ste 290, Beltsville MD 20705 | 301-474-0607 | www.dfrsolutions.com31
Natural Frequency
o 5mm Mesh, Natural Frequencieso 183 Hz
o 342
o 484
o 632
o 791
o 854
o Run time 52.5 seconds
o 2.5 mm Mesh, Natural Frequencieso 180 Hz
o 338
o 476
o 624
o 782
o 842
o Run time 582 seconds
© 2004 - 2007© 2004 - 20109000 Virginia Manor Rd Ste 290, Beltsville MD 20705 | 301-474-0607 | www.dfrsolutions.com32
Sherlock to Abaqus
o Geometry
model passed
into Abaqus
using Sherlock
Python script
o Remeshed with
all brick
elements
o Nf = 182 Hz
o Run time 175
seconds
© 2004 - 2007© 2004 - 20109000 Virginia Manor Rd Ste 290, Beltsville MD 20705 | 301-474-0607 | www.dfrsolutions.com33
Abaqus to Sherlock
o Abaqus model
modified and
imported back
into Sherlock
© 2004 - 2007© 2004 - 20109000 Virginia Manor Rd Ste 290, Beltsville MD 20705 | 301-474-0607 | www.dfrsolutions.com
o Choose the 2.5 mm mesh
o Smaller mesh only changes the
results by 0.5%
o Runtime is still manageable
Mesh Convergence
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© 2004 - 2007© 2004 - 20109000 Virginia Manor Rd Ste 290, Beltsville MD 20705 | 301-474-0607 | www.dfrsolutions.com
o The hard part
o What do the results mean?
o Overstress (stress or rupture – creep, plastic)
o Fatigue (strains – elastic, plastic, creep)
o Displacements (reflow simulations)
Post Processing
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Mechanical Fatigue
o Determine solder
joint strains at crack
initiation site
o Solder joint fatigue
3D, ¼ symmetric model
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Material Properties
o SnPb and SnAgCu modeled with multi-linear plasticity
o Copper modeled as elastic, perfectly plastic
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Plastic Strains in Solder Joint
o Plastic strain magnitudes recorded for crack initiation site
Equivalent plastic strains in SnAgCu solder
joint at 2400 µε
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Solder Stresses and Strains
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Fatigue Predictions Using Coffin-Manson
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Sherlock Post Processing
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• Sherlock does the post-processing and reliability
assessment
• Sherlock leverages the power of Abaqus to greatly
speed up the simulations and then does the post
processing to do the reliability assessment of
electronic assemblies
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Abaqus Integration
Mode 1: Sherlock manages all FEA processing
Mode 2: Export model from Sherlock to Abaqus
Mode 3: Import Abaqus FEA results into Sherlock for reliability analysis
ElectronicDesign Files
Life CycleConditions
3D Model /Analysis Steps
Pre-Processing
ReliabilityResults
3D Model /Disp Results /Strain Results
Post-Processing
PartsPackagesMaterials
FEATool
Abaqus
Model Results
FEAScript
SherlockDesign
Analysis
SherlockFailure
Analysis
SherlockData Store
• Transparent to the user
• Sherlock forms the input deck for Abaqus and runs the simulation with the Abaqus solver
• Sherlock automatically post processes the results and generates the reliability metrics
Mode 1
• Sherlock generated results
• Static displacement
Mode 1
• Sherlock generated results
• Random Vibration fatigue
Mode 1
Mode 2
• Automatic Python script generated models for Abaqus CAE
• Geometric based
• All material properties assigned
• Contact interactions formed
• Boundary conditions
• Analysis steps
• Results need to be imported intoSherlock forreliability assessment
Mode 3
• Model generated by Sherlock and modified and run in Abaqus CAE
Mechanical parts added, mesh changed, etc..
Mode 3
Mode 3
PCB Layer Modeling
• Thermal warpage during reflow simulation
• Sherlock contains FEA tools to speed Abaqus model development
• Two general techniques
• Geometric layer modeling
• Sherlock generates a Python script which converts the PCB plot layers into geometry
• Mosaic technique
• Sherlock generates an input deck with material properties assigned to the mesh
Package Warpage
The warpage analysis was plotted for a
temperature of 260C, with the reference
temperature 25C
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Thank you!
Questions??