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FreeTemp Manual,Version 2.05

Copyright © 2011 Advanced Thermal Engineering, Inc.

All Rights Reserved

P.O. Box 4528

Huntsville, AL 35815

USA

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Electronic Packaging forFree (Natural) Convection

1. Three Forms

2. FreeTemp, Orientations

3. FreeTemp, Controls

4. FreeTemp, CCA Thermal Management

5. The Thermal Solution Summary

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Electronic PackagingThree Forms

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Electronic Packaging FreeTemp, Orientations

This executable (52 KB) operates on a Windows Millennium Edition Platform or later.

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Electronic Packaging FreeTemp, Controls

•Solve for the printed wiring board (PWB) temperature.

•Move scroll bars and click option buttons to create an interactive trade study.

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Electronic PackagingFreeTemp, CCA Temperature Management

•Make the CCA compatible with the operating environment before the high hazard rates and low reliability cause a redesign.

•Solve the thermal problem before the environmental test fails and the CCA must be redesigned.

•Manage your resources before a conflict exists between disciplines.

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Electronic PackagingThe Thermal Solution Summary

•Electrical Engineers use it as a quick solution.

•Industrial (Reliability) Engineers use it as a simplified solution.

•Mechanical (Thermal) Engineers use it as a sanity check.

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Post Processing Values

1. Case Temperature

2. Junction Temperature

3. Reliability

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Case temperatureFree Convection

Calculate the Component Case Temperature for a case on a PWB cooled by free convection. The component power leaves the case by convection to the air passing over it. The air penetrates to the sides and top of the component case providing a large area for heat transfer. The surface area of the PWB component side approximates the total exposed surface area of all the components. The PWB temperature is now based on the component case temperature. Thus, the PWB and the component case are both at the same temperature.

Tcase = Tpwb

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Junction Temperature

Calculate the Component Junction Temperature.

Tjunc = Tcase + Rcj*Pcase

Where:

Tjunc is the component junction temperature.

Tcase is the component case temperature.

Rcj is the thermal resistance from the case to the junction.

Pcase is the component power dissipation.

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Reliability

Calculate the System Reliability. The Reliability Engineers calculate the component, card, and system reliability. It is based on the component characteristics. The hazard rate for each component is an input to the component reliability. This hazard rate is a function of the component junction temperature. A low component junction temperature produces a low component hazard rate. A component with a low hazard rate has high reliability. A chassis full of high reliability components has high system reliability.

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User’s Guide

1. FreeTemp, Version 2.05

2. Look and Feel of the Program

3. Forms of the Program

4. Navigating the Program

5. Manipulating the Program

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FreeTemp, Version 2.05Copyright © 2011 Advanced Thermal Engineering, Inc.

Free205.exe 52 KB

Lice205.pdf 7 KB

Read205.pdf 12 KB

The legal license is found in the two PDF files. Using the left mouse button, double-click the executable file to start the program. Select buttons to navigate the various forms.

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FreeTempLook and Feel of the Program

The selection of buttons will move the program forward or backward through the interactive forms. Scroll bars and option buttons will change default values to unique values. Moving through the forms will bring the user to the final temperature of a particular solution. Every form has a button to end the program.

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FreeTempForms of the Program

Table I. Form Titles

Name Title

Start: Form 1 (Orientation) Introduction (Form 1 of 3)

Form 2 (Input) PWB Mechanical Design (Form 2 of 3)

Finish: Form 3 (Input/Output) Free Convection Only (Form 3 of 3)

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The Electronic Box Navigating the Program

Start: Form 1

Finish: Form 3

Form 2

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The Electronic Box Manipulating the Program

When the program starts Form 1 is displayed. The user moves forward to change default values and complete his solution on Forms 2 and 3. If the results are not acceptable to the user, he simply returns to the second form to update new unique values for the design.

Start: Form 1

Finish: Form 3

Form 2

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Start: Form 1

1. Image

2. Options

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Form 1Image

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Form 1Options

1. Select “Forward” to see the next form.

2. Select “End the Program” to stop the program.

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Form 2

1. Image

2. Options

3. Details

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Form 2Image

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Form 2Options

1. Input “CCA Uniform Power”.

2. Input PWB Width, Height, and Ambient Air Temperature.

3. Select “Orient the CCA with Gravity” to move forward to the next form.

4. (Select “End the Program” if you wish to end the program session.)

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Form 2Details

1. The PWB width is 4800 mil (4.800”) and mounts the connector.

2. The PWB height is 4000 mil (4.000”, 10.1600 cm).

3. The components dissipate 1000 mW (1.000 W, 3.4130 Btu/hr).

4. The ambient air temperature boundary condition is 41.000°C (105.800°F).

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Finish: Form 3

1. Image

2. Options

3. CCA Descriptions

4. Details

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Form 3Image

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Form 3Options

1. Select an option button under “CCA Orientation”.

2. Select “Altitude”.

3. Select “Run”.

4. (Select “Card” to return to the first form.)

5. (Select “End the Program” if you wish to end the program session.)

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Form 3CCA Descriptions

This solution is a PWB in a housing. Free convection takes the heat from the component case to the PWB ambient air (boundary condition). The maximum, median, and minimum PWB temperatures are the same. The component case temperature is the same as the PWB temperature. This solution has free convection from the entire component side and thus prefers large boards.

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Form 3Details

1. This PWB temperature is 59.61°C, as are the component cases.

2. The ambient air temperature is 41.00°C.

3. The PWB surface coefficient is 0.7642 Btu/hr-ft2-°R at 5,000.0 feet.

4. The surface coefficient is less at high altitude. At 82,000 ft (82 Kft) it is gone!

5. If many different components are on the PWB, each one may be characterized by its own case temperature (Tcase), case exposed surface area (Acase), case power dissipation (Pcase), and the PWB surface coefficient (h_free) to the PWB ambient air temperature (Tsink).

Pcase=h_free*Acase*(Tcase-Tsink)

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References

1. Government References

2. Specific Reference

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Government ReferencesUnited States of America

Department of DefenseMilitary Handbooks

1. MIL-HDBK-217D, “Reliability Prediction of Electronic Equipment”, 15 Jan 1982.

2. MIL-HDBK-251, “Reliability/Design Thermal Applications”, 19 Jan 1978.

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Specific Reference

1. Cooling Techniques for Electronic Equipment, Dave S. Steinberg, John Wiley & Sons, New York, 1980, ISBN 0-471-04403-2.