Best Practices FEA Modeling - DfR Solutions

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.


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


6

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


8

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


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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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

16


Geometry Generation

17


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

19

Via in Pad Plated Over (ViPO)


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

20


o Have Abaqus to ignore

certain features

Example: Virtual Topology

21


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

22


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

23


Assembly

24


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

25


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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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


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


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


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


Abaqus to Sherlock

o Abaqus model

modified and

imported back

into Sherlock


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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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


Material Properties

o SnPb and SnAgCu modeled with multi-linear plasticity

o Copper modeled as elastic, perfectly plastic


Plastic Strains in Solder Joint

o Plastic strain magnitudes recorded for crack initiation site

Equivalent plastic strains in SnAgCu solder

joint at 2400 µε


Solder Stresses and Strains


Fatigue Predictions Using Coffin-Manson


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

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

52

Thank you!

Questions??

Best Practices FEA Modeling - DfR Solutions

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