Thermal Stress Analysis of an Integrated Circuit Board

Chapter 46: Thermal Stress Analysis of an Integrated Circuit Board

46 Thermal Stress Analysis of an Integrated Circuit Board

Summary 921

Introduction 922

Modeling Details 922

Solution Highlights 924

Results 925

Modeling Tips 926

Pre- and Postprocess with SimXpert 927

Input File(s) 969

Video 970

921CHAPTER 46

Thermal Stress Analysis of an Integrated Circuit Board

SummaryTitle Chapter 46: Thermal Stress Analysis of an Integrated Circuit Board

Features Chaining thermal and stress analysis in one execution

Geometry

Material properties

Analysis characteristics Nonlinear thermal analysis followed by a stress analysis

Boundary conditions

Thermal boundary conditions: The heat flux is applied on top surface of the chip with heat flux equal to 0.025 W/(mm2 oC). Convection heat transfer with ambient (at 70 oC). Top surface of the case - 4.05x10-5 W/(mm2 oC). Bottom Surface of the case - 2.026x10 -5 W/(mm2 oC) Sides (adjacent to the lead frame where it is fixed) - 7.0x10-5. There is radiation loss on top of the outer case to ambient at 40 oC with emissivity equal to 0.8 and view factor is 1.0. Structure boundary conditions: Fix the end of the lead frame.

Element type 8-node CHEXA

FE results Thermal contours and resulting displacement contours

Chip

Leads

Case

Paste

1

Units: mm, N, C

14 x 14 x 3.22

111

Material k E

Lead frame 0.147 6.9x104 1.0x10-6

Chip 0.168 5.52x104 1.0x10-5

Case 0.0714 4.5x104 1.0x10-6

Paste 0.02016 2.0x103 1.0x10-5

W mm C N mm2 (1/C)

Thermal Contours Displacement Contours

MD Demonstration Problems

CHAPTER 46922

IntroductionThis example demonstrates the chaining of thermal and structural analysis in SOL 400 whereby the first step is a nonlinear steady state thermal analysis subject to heat flux on the chip, convection and radiation boundary conditions, and the second step is a nonlinear static analysis using the temperatures from the first step. The thermal stress analysis chaining has always been available in the linear heat transfer to linear static analysis using param, heatstat,yes in the SOL 101 run. However, it was not possible previously in Nastran to run a nonlinear heat transfer followed by the static analysis in a single execution because SOL 101 is a linear heat transfer solution. The only alternative is to run a nonlinear thermal analysis using SOL 153 and used the resulting temperature punch file as the input thermal load for your stress analysis. The user can output a punch file by specifying TEMP(PRINT,PUNCH)=all in the first run. This will create a punch file that consists of temperature for every grids in the model. In the thermal stress run he can use the TEMP(LOAD)=1 in the case control to use the temperature load in the static run. Chaining of thermal and structural analyses facilitates design studies based on:

1. changing the materials properties

2. changing the thermal boundary conditions

3. changing structure constraints

whereby the temperatures as well as the corresponding displacements are visualized in a single run.

Modeling DetailsBonded joints are used in the design of a circuit board. A change in temperature due to the equipment operation can introduce stresses in joined materials of dissimilar thermal expansion coefficient. In this case we have chip heating due to the applied power, causing thermal gradients in the different materials which, together with the fixed displacements cause high stresses near the end of the lead frame.

The chip dimension (Figure 46-1) is 3.80 mm by 3.80mm with thickness equal to 0.7 mm. It is mounted on top of adhesive (paste). The outer case dimension is 14 mm by 14 mm by 3.22 mm.

Figure 46-1 Chip, Paste, and Lead Frame (Nastran Test File: hybrid_radbc_unit.dat)

Chip

923CHAPTER 46


Figure 46-2 Outer Case

A heat flux is applied to the top surface of the chip with heat flux equal to 0.025 W/(mm2oC). The top surface, bottom surface and the sides (adjacent to the lead frame where it is fixed) of the case are subjected to convection heat loss.

Heat is convected to the environment at 70oC. The respective heat transfer coefficient for the top, bottom and sides

are 4.05x10-5 W/(mm2oC), 2.026x10-5 W/(mm2oC) and 7.00x10-5 W/(mm2oC). Finally there is a radiation loss on top

of the outer case to ambient environment of 40oC with emissivity equal to 0.8 and view factor is 1.0.

The structural boundary conditions include fixing the end of the lead frame as shown in Figure 46-3.

Figure 46-3 Structural Boundary Conditions

The material properties are shown in Table 46-1.

In running a thermal stress analysis, it is important to check you have specified a thermal coefficient of expansion on the field 7 on the MAT1 bulk data entry. Otherwise, there will be no thermal expansion in your problem.

Table 46-1 Material Properties

Material k E

Chip 0.147 6.9x104 1.0x10-6

Lead Frame 0.168 5.52x104 1.0x10-5

Case 0.0714 4.5x104 1.0x10-6

Paste 0.02016 2.0x103 1.0x10-5

14 x 14 x 3.22

W mm K– N mm2 (1/C)


CHAPTER 46924

It is important that you have a consistent set of units. In this case, the thermal conductivity has units of W/(mm2 K),

and therefore your Young's modulus should be in the unit of N/(mm2). This consistency also applies to the Stefan-

Boltzmann constant also used in the radiation boundary conditions with units of W/(mm2 K).

Solution HighlightsThe following are highlights of the Nastran input file necessary to model this problem:

$! NASTRAN Control SectionNASTRAN SYSTEM(316)=19$! File Management Section$! Executive Control SectionSOL 400CENDECHO = SORT$! Case Control SectionTEMPERATURE(INITIAL) = 33SUBCASE 1$! Subcase name : NewLoadcase$LBCSET SUBCASE1 ANALYSIS = NLSTATSTEP 1$LBCSET STEP1.1 Thermal$! Step name : Thermal ANALYSIS = HSTAT SPC = 36 LOAD = 37 NLSTEP = 2 TSTRU = 38 THERMAL(SORT1,PRINT)=ALL FLUX(PRINT)=ALLSTEP 2$LBCSET STEP1.2 Structural$! Step name : Structural SPC = 11 ANALYSIS = NLSTAT NLSTEP = 3 TEMPERATURE(LOAD) = 38 DISPLACEMENT(SORT1,PRINT,REAL)=ALL STRESS(SORT1,PRINT,REAL,VONMISES,CORNER)=ALLBEGIN BULK$! Bulk Data Pre SectionPARAM SNORM 20.PARAM K6ROT 100.PARAM WTMASS 1.PARAM LGDISP 1PARAM TABS 273.15PARAM* SIGMA 5.6699E-14PARAM POST 1$! Bulk Data Model Section

925CHAPTER 46


There are two steps in this analysis. The first step is associated with the thermal boundary conditions as indicated with ANALY=HSTAT. The second step is the thermal stress analysis and the structure boundary condition which the ANALY=NLSTAT. The TEMP(load)=1 in the second step will allow the Step 2 to pick up the calculated temperature from step 1 as the thermal load for the calculation of thermal stress. Please note that the param,lgdisp,1 is required when chaining thermal and structural analyses. The TEMP(INITIAL)=9 points to the TEMPD,9,0.0 in the bulk data section. This indicates the initial stress free temperature is at zero degrees. The thermal strain is then equal to the product of the linear coefficient of thermal expansion times the change in temperature. In this example, the thermal coefficient of expansion is constant, temperature dependency is also readily possible.

Following is the output from the thermal analysis and thermal stress analysis.

1 JUNE 11, 2010 MD NASTRAN 5/21/10 PAGE 896 0 SUBCASE 1 STEP 1 LOAD STEP = 1.00000E+00 T E M P E R A T U R E V E C T O R POINT ID. TYPE ID VALUE ID+1 VALUE ID+2 VALUE ID+3 VALUE ID+4 VALUE ID+5 VALUE 6320 S 8.666747E+01 8.661747E+01 8.657528E+01 8.654037E+01 8.651233E+01 8.649082E+01 6327 S 8.697186E+01 8.687786E+01 8.679778E+01 8.672908E+01 8.667010E+01 8.661977E+01 6333 S 8.657732E+01 8.654223E+01 8.651408E+01 8.649251E+01 8.647716E+01

1 JUNE 11, 2010 MD NASTRAN 5/21/10 PAGE 9546 0 SUBCASE 1 STEP 2 LOAD STEP = 1.00000E+00 D I S P L A C E M E N T V E C T O R POINT ID. TYPE T1 T2 T3 R1 R2 R3 99 G -7.002653E-04 -5.229975E-04 1.484855E-03 0.0 0.0 0.0 100 G -8.090116E-04 -5.227823E-04 1.456455E-03 0.0 0.0 0.0 101 G -8.938556E-04 -5.234344E-04 1.425087E-03 0.0 0.0 0.0 102 G -1.037468E-03 -5.227153E-04 1.400765E-03 0.0 0.0 0.0 103 G -1.272494E-03 -4.961967E-04 1.366653E-03 0.0 0.0 0.0

Results

Figure 46-4 Temperature Contours


CHAPTER 46926

Figure 46-5 Resulting Displacements (Magnified Displacements for Deformed Plot)

Figure 46-6 von Mises Stress Contour at Five Seconds

Modeling TipsAlways check consistency of units; the basic units are mm, N, and oC(K).

$watt/mm.CMAT4 1 .147 1. 1.$ Material Record : mat1.2$ Description of Material :MAT4 2 .168 1. 1.$ Material Record : mat1.3$ Description of Material :MAT4 3 .0714 1. 1.$ Material Record : mat1.4$ Description of Material :MAT4 4 .02016 1. 1.$

927CHAPTER 46


MAT1,1,6.9e4,,0.3,,1.0e-6$ Material 2 : leadframeMAT1,2,5.52e4,,0.3,,1.0e-5 $ Material 3 : newMAT1,3,4.5e4,,0.3,,1.0e-6 $ Material 4 : pasteMAT1,4,2.0e3,,0.3,,1.0e-5

Pre- and Postprocess with SimXpertThis example shows how to use SimXpert for a chained thermal/stress analysis. It will create thermal lbcs for normal heat flux, normal convection, and radiation to space. It will also create the structural lbc for pinned ends to electrical leads. The thermal/stress analysis simulation parameter values will be defined. The results can be viewed after the thermal/stress analysis is performed.

Units

a. For default workspace, select Structures

a


CHAPTER 46928

Specify the Model Units

a. Tools: Options

b. Observe the User Options Window

c. Select Units Manager

d. For Basic Units, specify the model units:

e. Length = mm; Mass = g; Time = s; Temperature = celsius, Force = N

f. Click OK

a b

c e

d

929CHAPTER 46


Import FE Model into Separate Parts

a. Import finite element model into separate parts

b. Tools: Options

c. General: input/Output/Nastran.Sturctures

d. Unselect Reduce Parts

e. Click OK

WS9-82009 MSC.Software Corporation

c

e

d


CHAPTER 46930

Import MD Nastran Nodes and Elements File

a. Import MD Nastran nodes and elements file

b. File: Import/Nastran

c. Select nug_46_bdf.bdf

d. Click OK

b

c

931CHAPTER 46


MD Nastran Nodes and Elements Model

a. MD Nastran nodes and elements model

b. Model Views: Isometric View

c. Render FE Shaded with Edges

d. View Manipulation: Fill

b c


CHAPTER 46932

Material Properties

a. Material properties of the imported model

b. Double click, one at a time, on each of the four material names

c. Observe the thermal-mechanical contents of the material forms

d. Click Cancel

b

c

933CHAPTER 46


Material Properties (continued)

a. Material properties of the imported model


c. Click Thermal tab

d. Observe the thermal contents of the material forms

e. Click Cancel

WS9-12

b

c

d


CHAPTER 46934

Element Properties

a. Element properties of the imported model


c. Observe the element property contents of the property forms

d. Click Cancel

b

c

935CHAPTER 46


Apply Normal Heat Flux

a. Create applied heat flux. Apply it to the top of the chip

b. Display just the chip by hiding everything else. Right click SOLID_5_nug_46_bdf.bdf;

then select Show Only

c. Observe the chip element only

d. Use Model Views: Isometric or Left

e. LBCs tab: Heat Transfer/Normal Flux

f. For Name, enter Normal Flux_Top_Chip

g. For Entities screen, select the nodes at the top of the chip

h. For Heat Flux, enter 9.025

i. Click OK

.

.

.b

e

i

g

f

g

h


CHAPTER 46936

Normal Heat Flux Applied to Top of Chip

a. Create applied heat flux. Apply it to the top of the chip

b. Observe the heat flux markers

c. Show the entire model

d. Change the color of the markers to red using the Visualize tab for the LBC

b c

937CHAPTER 46


Free Convection Applied to Top of Case

a. Create applied free convection. Apply it to the top of the case

b. Model Views: Left

c. LBCs tab: Heat Transfer/Free Convection

d. For Name, enter Free Convection_Top_Case

e. For Ambient temperature, enter 70

f. For Entities screen, select all the nodes at the top of the case

g. Click Advanced

h. For Convection coefficient, enter 4e-5

i. Click OK

c

h

fe

d

i

g

f


CHAPTER 46938

Model with Heat Flux and Free Convection on Top

a. Observe the entire model with normal heat flux on the chip and free convection on the top

of the case

a

939CHAPTER 46


Free Convection Applied to Sides of Case


b. Model Views: Top

c. Hide the lead frame

d. LBCs tab: Heat Transfer/Free Convection

e. For Name, enter Free Convection_Sides_Case

f. For Ambient temperature, enter 70

g. For Entities screen, select all the nodes at two sides of the case

h. Click Advanced

l. For Convection coefficient, enter 7e-5

j. Click OK

g

g

i

d

e

f

h

j

c


CHAPTER 46940

Model with Heat Flux and Free Convection to Sides

a. Observe the entire model with normal heat flux on the chip and free convection on the top

and two sides of the case

a

941CHAPTER 46


Free Convection Applied to Bottom of Case



c. LBCs tab: Heat Transfer/Free Convection

d. For Name, enter Free Convection_Bottom_Case

e. For Ambient temperature, enter 70

f. For Entities screen, select all the nodes at the bottom of the case

g. Click Advanced

h. For Convection coefficient, enter 2.02e-5

i. Click OK

c

h

fe

d

i

g

f


CHAPTER 46942

Model with Heat Flux and Free Convection on Case

a. Observe the entire model with normal heat flux on the chip and free convection on the top,

two sides, and bottom of the case

a

943CHAPTER 46


Entire Model with Lead Frame

a. Observe the entire model with the lead frame

b. Show the lead frame

a


CHAPTER 46944

Radiation to Space Applied to Top of Case

a. Create radiation to space. Apply it to the top of the case


c. LBCs tab: Heat Transfer/Rad to Space

d. For Name, enter Rad to Space_Top_Case

e. For Entities screen, select all the nodes at the top of the case

f. For Ambient temperature, enter 40

g. For Viewfactor, enter 1.0

h. Click Advanced

i. For Absorptivity, enter 1

j. For Emissivity, enter 1

k. For Shell surface option, select Front

l. Click OK

.

c

h

fe

d

l

g

kj

i

e

945CHAPTER 46


Model with Radiation to Space

a. Observe the entire model with normal heat flux, free convection, and radiation to space

on the case

a


CHAPTER 46946

Define Structural LBC

a. Create a structural lbc for the stress analysis

b. LBCs tab: LBC Set/LBC Set

c. For Name, enter Structural

d. Click OK

e. This LBD set will be populated subsequently

b

d

c

947CHAPTER 46


Create Pinned Constraint at Toe of Lead Frame

a. Create a structural pinned lbc constraint at the toe of the lead frame

b. LBCs tab: Constraints/Pin

c. For Name, enter Pinned Constraint_Toe_Lead

d. Use Model Views: Left or Front

e. For Entities screen, select the toe lead frame nodes

f. Click OK

b

c

f

e

e e


CHAPTER 46948

Model with Structural Pinned Constraint

a. Observe the model with structural pinned constraints

a

949CHAPTER 46


Create SimXpert Analysis File

a. Create a SimXpert analysis file for MD Nastran

b. Right click on nug_46_bdf.bdf

c. Select Create new Nastran job

d. For Job Name, enter ch46

e. For Solution TYpe, select SOL400

f. For Solver Input File, select the path

g. Unselect Create Default Layout

h. Click OK

b

c

h

g

f

e

d


CHAPTER 46950

Create SimXpert Analysis File (continued)


b. Right click on Load Cases

c. Select Create Loadcase

d. For Name (Title), enter NewLoadcase

e. For Analysis TYpe, select Nonlinear Steady Heat Trans

f. Click OK

b

c

f

e

d

951CHAPTER 46




b. Right click on Load Steps

c. Select Create Loadstep

d. For Name (Title), enter Thermal

e. For Analysis TYpe, select Nonlinear Steady Heat Trans

f. Click OK

bc

f

e

d


CHAPTER 46952



b. Right click on Load Steps

c. Select Create Loadstep

d. For Name (Title), enter Structural

e. For Analysis TYpe, select Nonlinear Static

f. Click Use Temperature Set from Preceeding Heat Transfer Step

If Applicable

g. Click OK

b

c

f

e

d

g

953CHAPTER 46




b. Right click on Load/Boundaries

c. Select Select Lbc Set

d. For Selected Lbc Set, select DefaultLbcSet

e. Click OK

b

c

e

d


CHAPTER 46954



b. Double click on Solver Control

c. Select Solution 400 Nonlinear Parameters

d. For Default Init Temperature, enter 0

e. For Large Displacement, select Large Disp and Follower Force

b

c

e

d

955CHAPTER 46




b. For Absolute Temperature Scale, select 273.15 Degree Celsius

c. For Stefan Boltzmann Constant, select 5.6699E-14 WATTS/mm2/K4

d. Click Apply (not shown)

e. Click Close (not shown)

bc


CHAPTER 46956




c. Select Output File Properties

d. For Text Output, select Print

e. Click Apply

f. Click Cost

b

d

f

d

c

957CHAPTER 46




b. Double click on Loadcase Control

c. Select Subcase Steady State Heat Transfer Parameters

d. Click Temperature Error

e. For Temperature Tolerance, enter 0.01

f. Click Load Error

g. For Load Tolerance, enter 1e05

h. Click Apply (not shown)

i. Click Close (not shown)

c

d

fe

g

b


CHAPTER 46958



b. Right click on Output Requests

c. Select Nodal Output Requests

d. Click Create Temperature Output Request

e. Click OK

b

c

e

d

959CHAPTER 46




b. Right click on Output Requests

c. Select Elements Output Requests

d. Click Create Element Stress Output Request

e. Click OK

b

c

e

d


CHAPTER 46960



b. Right click on ch46

c. Select Run

b c

961CHAPTER 46


Attach SimXpert Results File

a. Attach a SimXpert MD Nastran results file

b. File: Attach Results

c. For File path, select ch46.xdb

d. Click OK

b

c

d


CHAPTER 46962

Display Thermal Results

a. Display temperature results as a fringe plot

b. Results tab: Results/Fringe

c. For Result Cases, select SC1: Non.-linear: 100 % of Load

d. For Result type, select Temperatures

e. Click Update

b

c d

e

963CHAPTER 46


Display Thermal Results (continued)

a. Observe the temperature results

a


CHAPTER 46964

Display Structural Results using OP2 File

a. To display the structural results for the R3.2 release of SimXpert, use an .op2 file


c. Select Output File Properties

d. For Binary Output, select OP2

e. Click Apply

f. Click Cost

b

f

e

d

c

965CHAPTER 46


Perform a SimXpert Analysis for OP2 Results File

a. Perform a SimXpert analysis using MD Nastran

b. Right click ch46

c. Select Run

b

c


CHAPTER 46966

Detach .xdb Thermal Results File

a. Before attempting to attach the .op2 file, detach the .xdb file

b. File: Detach Results file

c. Select ch46.xdb

d. Select OK

e. Click Yes

b

967CHAPTER 46


Attach SimXpert Results OP2 File

a. Attach a SimXpert MD Nastran results file

b. File: Attach Results

c. For File Path, select ch46.op2

d. Click OK

b

c

d


CHAPTER 46968

Display Structural Results using OP2 File

a. Display von Mises results as a fringe plot

b. Results tab: Results/Fringe

c. For Result Cases, select SC1: Step 2: Non-linear: 100 % of Load

d. For Result type, select Stress Tensor

e. For Derivation, select von Mises

f. Click Update

.

b

c

df

e

969CHAPTER 46


Display Structural Results using OP2 File (continued)

Input File(s)

a. Observe the von Mises stress results

File Description

nug_46.dat MD Nastran chaining thermal and thermal stress test file.

Ch46.SimXpert SimXpert data corresponding to above

a

http://www.mscsoftware.com/doc/nastran/mdug/input_files/ch046/Ch46.SimXpert

http://www.mscsoftware.com/doc/nastran/mdug/input_files/ch046/nug_46.dat


CHAPTER 46970

VideoClick on the image or caption below to view a streaming video of this problem; it lasts approximately 28 minutes and explains how the steps are performed.

Figure 46-7 Video of the Above Steps

Thermal Contours Displacement Contours

http://www.mscsoftware.com/training_videos/mdug/ch046/2010/ch046.swf

http://www.mscsoftware.com/training_videos/mdug/ch046/2010/ch046.swf

Documents

Thermal Stress Analysis of an Integrated Circuit Board