Convection Correlations for PCB

8/9/2019 Convection Correlations for PCB

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Chapter 65: Convection Correlations for PCB

65 Convection Correlations for

Printed Circuit Board (PCB)

Summary 1209

Introduction 1210

Modeling Details 1210

Solution Highlights 1210

Results 1218

Modeling Tips 1219

Input File(s) 1219

Video 1219


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1209CHAPTER 65

Convection Correlations for Printed Circuit Board (PCB)

Summary

Title Chapter 65: Convection Correlations for PCB

Features Natural convection correlation 701 by using PCONV1 entry

Forced convection correlation 507 by using PCONV1 entry

Contact loads by using PRJCON and SET3 cards

Geometry

The dimension of PCB is 9 x 6 x 0.0093 inches (copper thickness)

Material properties PCB: Copper K = 9.9 W/in C; Copper Thickness = 0.0093 in

Chips: K = 2.24 W/inC

Air: K = 6.66e-4 W/inC; Cp = 456.2 J/lbmC; = 5.01e-5 lbm/in; = 1.03e-6 lbm/in s, = 3.43e-3/C

Analysis characteristics Solution 400/RC Network solver. Steady state thermal analysis.

Boundary conditions Wall temperature = 25C

For Natural convection model: Tair = 20C

For Forced convection: Inlet Air Temperature = 20C

Applied loads Total surface heat = 5W, Total Heat on chips: 7.5W, 5W, 5W

Contact load between PCB and chips with coefficient =12 W/in C Convection with correlation 701 for natural convection model

Coupled advection with correlation 507 for forced convection model

Mass flow rate = 3.2E-3 lbm/s

Hydraulic Diameter = 0.2 in

Flow Cross Section = 0.6 in

Interval between chips and next PCB = 0.1 in

Element type CQUAD4 for PCB

CTETRA for chips CHBDYP/FTUBE for air flow (for natural convection model)

FE results Temperature result:


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MD Demonstration Problems

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Introduction

This problem demonstrates the convection correlation feature of SOL 400 RC Network Solver.

Modeling DetailsThe dimension of PCB is 9 x 6 x 0.0093 inches (copper thickness). The two edges are fixed to the slots and have a

constant boundary temperature of 25C. The total circuit power on the PCB is 5W, and the total power of the three

chips is 7.5W, 5W, and 5W, respectively. The PCB mesh and chip mesh do not match each other. RC Network Solver

has a special contact algorithm to deal with that.

The convection correlation 701 is used to simulate the natural convection of PCB and chips. The air temperature is

20C. The convection correlation 507 is used to simulate the forced convection. The forced convection is applied to

both sides of the PCB and outer side of the chips. The inlet air temperature is 20C.

Figure 65-1 PCB and Chips Model

Figure 65-2 Natural and Forced Convection Models

Solution HighlightsConvection correlations are used to calculate the convection coefficients in different situations. MD Nastran RC

Network Solver supports 44 convection correlations. Each convection correlation consists of three tabs: CorrelationView, Variables, and Additional Coefficient. Correlation View form includes the description, formula, illustration, and

5 W

Constant Boundary Temperature = 25 CoContact Coefficient = 1.2 W/in C2 o

20 Co

20 Co

Inlet T = 20 Co0.1 in


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1211CHAPTER 65


some geometry related parameters. These parameters are also displayed in the Variable form, along with the fluid

material parameters. Additional Coefficient is reserved for future use for some P/Thermal correlations.

Figure 65-3 Natural Convection Correlation 701 Forms

The natural convection model defines the convection correlation 701 by using PCONV1 entry, which is referenced by

CONV entry. The following are the highlights of the Nastran input file necessary to model the natural convection

problem with convection correlations:

......


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Figure 65-4 Forced Convection Correlation 507 Forms

The forced convection model uses the coupled advection load to link the fluid stream and surfaces. Instead of a

constant convection coefficient, a convection correlation is used to calculate the convection coefficient at run time.

PCONV1 entry defines the forced convection correlation 507. This entry is referenced by the CHBDYP and PRJCON

cards. The following are the highlights of the Nastran input file necessary to model the forced convection problem

with convection correlations:

......

......

......

......


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PRJCON entry is used to link the two SET3 cards. A convection correlation PID (PCONV1 ID) is referenced if the

HEAT2 option is used. The inlet temperature is defined as a SPC for each inlet node of the fluid stream.


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Defines the properties required to calculate convective heat transfer. It can exist in a simple mode with convection

coefficient defined in the MID or in advanced mode where the H value is calculated using the geometric parameters and

referenced material.

Format

Example

PCONV1 Thermal Convection Calculation Properties

1 2 3 4 5 6 7 8 9 10

PCONV1 PID Corr ID MID Mdot Velocity Length or

Diameter

Flow Cross

Section

+

+ Length

function

type

Flow Cross

Section

type

Mdot f Velocity f Length or

Diameter f

Flow Cross

Section f

+

+ C1 C2 C3 C4 C5 C6 C7 C8 +

+ C9 C10 C11 C12 C13 C14 C15 C16 +

+ C17 C18 C19 C20 C21 C22 C23 C24

1 2 3 4 5 6 7 8 9 10

PCONV1 2 701 2 1.0

Field Contents Type Default

PID Property identification number, referenced by CHBDYP

and/orCONV.

I 0

Corr ID ID of convection type in correlation library. I 0 0

MID Material identification number for convection

calculation.

I 0 0

Mdot Mass flow rate. R 0.0

Mdot f Mass flow rate TABLEDj table ID. I 0 0

Velocity Fluid velocity. R 0 0.0

Velocity f Fluid velocity TABLEDj table ID. I 0 0Length or Diameter Geometry, based on Corr ID. R 0.0 0.0

Length or Diameter f type Geometry function type: I 0 2

1 = time

2 = temperature

Length or Diameter f Geometric function TABLEMj orTABLEDj table ID I 0 0

Flow Cross Section Flow Cross Section. R 0.0 0.0


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Remarks

1. This entry is for RC Network solver only.

2. The PCONV1 entry contains the properties for a CONV and CHDBYP, and can be used for connecting with a

PRJCON. PID must be unique to both the PCONVID in PCONV and the PID in PHBDY. This will be the ID

referenced by CONV, PRJCON, and CHBDYP.

3. MATID must reference a MAT4 fluid material.

4. For Corr. ID and C1 thru C24, please referenceMSC SINDA Users Guide and Library Reference or

P/Thermal Users Guide.

Flow Cross Section f type Flow Cross Section function type I 0 2

1 = time

2 = temperature

Flow Cross Section f Flow Cross Section function TABLEMj orTABLEDj table

ID.

I 0 0

C1 thru C24 Geometric properties based on chosen convection

correlation

R 0.0



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Specifies a thermal connection between two regions of elements. The connection is automatically determined

geometrically as a projection of the slave region on to the master, and the strength of the connection is calculated based

on the properties given.

HEAT1

Format

Example

HEAT2

Format

Example

HEAT3

Format

PRJCON Thermal RC Element Contact

1 2 3 4 5 6 7 8 9 10

PRJCON BID +

HEAT1 SET3

Master

SET3 Slave h

1 2 3 4 5 6 7 8 9 10

PRJCON 1

HEAT1 1 2 1.2

1 2 3 4 5 6 7 8 9 10

PRJCON BID +

HEAT2 SET3

Master

SET3 Slave PID

1 2 3 4 5 6 7 8 9 10

PRJCON 1

HEAT2 1 2 1001

1 2 3 4 5 6 7 8 9 10

PRJCON BID +

HEAT3 SET3

Master

SET3 Slave F Emis

Master

Emis Slave


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Example

HEAT4

Format

Example

1 2 3 4 5 6 7 8 9 10

PRJCON 1

HEAT3 1 2 1. 0.85 0.5

1 2 3 4 5 6 7 8 9 10

PRJCON BID +

HEAT4 SET3

Master

SET3 Slave F RADC id

Master

RADC id

Slave

1 2 3 4 5 6 7 8 9 10

PRJCON 1

HEAT4 1 2 1. 1001 1002


BID BCBODY identification number. I 0 Required

HEATx Indicates the start of HEAT elements. C

SET3 Master ID of the master element collection for connection. I 0 Required

SET3 Slave ID of the slave element collection for connection. I 0 Required

h Convection correlation. R 0.0 Required

forHEAT1

PID PID of the property to be used forh value. I 0 Required

forHEAT2

F View factor between parts. 0.0 R

1.0

Required

forHEAT3& HEAT4

Emis Master Emissivity of master collection. R 0.0 Required

forHEAT3

Emis Slave Emissivity of master collection. R 0.0 Required

forHEAT4

RADC id Master RADMID of the material to be used for master emissivity

value.

I 0 Required

RADC id Slave RADMID of the material to be used for slave emissivityvalue.

I 0 Required


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Remarks

1. This HEATx and the later parameters are for RC Network solver only.

2. For HEAT2, PID must refer to a PCONV1 type, and not a PCONV orPCONVM.

3. RC Network Solver uses a projection method to determine the connection (not the nearest neighbor method).

In most of the cases, the projection method is more accurate than the nearest neighbor method.

Results

Figure 65-5 Temperature Contour of PCB with Natural Convection

Figure 65-6 Temperature Contour of PCB with Forced Convection

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For now, SimXpert can not display the temperature contour on the fluid stream. Apparently, the cooling effect of the

forced convection is much better than the natural convection.

Modeling TipsIn SimXpert Structural workspace, when you pick the back face of the solid chips for the contact loads, you may need

to hide the PCB surface first, so that the back face of the solid chips can be picked correctly.

The convection correlations are defined in Material and Property/1D Properties / Correlation. If you want to use

constant convection coefficient in the coupled advection loads, please select the 1D Fluid Flow option. If you want to

use convection correlation to calculate the convection coefficient, please pick the Convection Correlation option.

Input File(s)

VideoClick on the image or caption below to view a streaming video of this problem; it lasts approximately 30 minutes and

explains how the steps are performed.

Figure 65-7 Video of the Above Steps

Files Description

QT22_pcb_natural.dat MD Nastran SOL400/RC Network Solver thermal input file

QT25_pcb_forced.dat MD Nastran SOL400/RC Network Solver thermal input file
http://www.mscsoftware.com/training_videos/mdug/ch065/2010/ch065.swfhttp://www.mscsoftware.com/doc/nastran/mdug/input_files/ch065/QT22_pcb_natural.dathttp://www.mscsoftware.com/doc/nastran/mdug/input_files/ch065/QT25_pcb_forced.dathttp://www.mscsoftware.com/training_videos/mdug/ch065/2010/ch065.swfhttp://www.mscsoftware.com/training_videos/mdug/ch065/2010/ch065.swfhttp://www.mscsoftware.com/doc/nastran/mdug/input_files/ch065/QT25_pcb_forced.dathttp://www.mscsoftware.com/doc/nastran/mdug/input_files/ch065/QT22_pcb_natural.dat

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Convection Correlations for PCB