Managing Heat for Reliability

Brian Piercy & David ChapmanGSI Marketing & Apps Eng.

2

Thermal Density Increasing

1 BTU 1 BTU

25°C 95°C

Equal thermal energy in a smaller volumeresults in higher temperature.

3

Radiation Rate DecreasingOlder, larger

parts had more surface areaand smaller

Theta JA

Newer, smallerparts have less

surface areaand largerTheta JA

4

Thermal Path to the Board is Getting Much Better

SmallerTheta JB

LargeTheta JB

5

Hot Hosts Cook RAMs

A nearby processor or FPGA makes thermal analysis based on Theta JA

alone impossible.

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Theta JA Theta JA

“The intent of θJA measurements is solely for a thermal performance comparison of one package to another in a standardized environment. This methodology is not meant to and will not predict the performance of a package in an application-specific environment.”

JEDEC Standard JESD51-2A:Integrated Circuits Thermal Test Method Environmental Conditions - Natural Convection (Still Air)www.jedec.org/sites/default/files/docs/JESD51-2A.pdf

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Thermal Power Circuit

Ambient Temperature

PCB Temperature

RAM Power

Case-to-AmbientThermal Resistance

Junction-to-CaseThermal Resistance

Junction-to-BoardThermal Resistance

PCB-to-AmbientThermal Resistance

PCB Thermal Resistance

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3D Analysis is Required

Thermal Design tools like Flowtherm™ account for all heat sources, thermal sinks and thermal resistances simultaneously.

http://www.mentor.com/products/mechanical/products/flotherm

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Predicting Die Temp

• Complex analysis is required to predict the actual temperatures at various places in and around the RAM.

• Approximate results can be obtained IF the RAM is physically connected to an object with high thermal mass via a path with low thermal resistance.

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LR-HM Thermal Estimates

Focus on a LOW RESISTANCE path to a HIGH MASS object.

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Assume PC Board as Thermal Constant30°C Air

1.5 W Die

2.5°C/W JC

10°C/W JB

Tj = (Theta JB * Pd) + TbTj = (10°C/W * 1.5 W) + 50°CTj = 65°C

So…

Tc = Tj - (Theta JC * Pd)Tc = 65°C – (2.5°C/W * 1.5W)Tc = 61.25°C

So…

Tj < 65°C.

RAM will heat air and air will cool the RAM…some…

65°CDie

61.25°CCase Top

50°CBoard

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Assume Cold Plate and PCB as Thermal Constant

1.5 W Die

2.5°C/W JC

10°C/W JB

Tj = Tc + (Theta JC * Pd)Tj = 20°C + (2.5°C/W * 1.5W)Tj = 23.75°C

And…

Tj = (Theta JB * Pd) + TbTj = (10°C/W * 1.5 W) + 50°CTj = 65°C

So…

65°C > RAM Tj > 23.75°C

20°CCase Top

50°CBoard

20°CCold Plate

50°CRAM Balls

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Design vs. Characterization

A single thermal resistance parameter cannot be used alone to predict die temperature.

However…

Theta JC (Junction to Case Temperature), Theta JB (Junction to Board Temperature), measured Case Temperature and measured Board Temperature can be used to estimate actual Junction temperature.

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Thermal Characterization

Measured Total DiePower = 2.0 W

Board to JunctionTj = (Theta JB * Pd) + TbTj = (12.3°C/W * 2.0W) + 30°CTj = 54.6°C

Case to JunctionTj = (Theta JC * Pd) + TcTj = (2.6°C/W * 2.0W) + 50°CTj = 55.2°C

So…

Junction Temp 55°C*

* Do not expect to get exactly the same answer for each method!

Data SheetThermal

CharacteristicsJB = 12.3°C/WJC = 2.6°C/W

Measured BoardTemp = 30°C

MeasuredCase Temp = 50°C

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Data Sheet Specifications• Absolute Maximum Ratings

• Define the worst environment the device can tolerate for a short time.

• Exposing a device to Absolute Maximum conditions reduces device lifetime.

• Recommended Operating Conditions• The device is guaranteed to meet all

specifications• A group will demonstrate a Failure Rate of no

greater than 50 FITs for 10 years.

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Example Abs Max SectionAbsolute Maximum Ratings(All voltages reference to VSS)Symbol Description Value Unit

VDD Voltage on VDD Pins –0.5 to 2.4 VVDDQ Voltage in VDDQ Pins –0.5 to VDD VVREF Voltage in VREF Pins –0.5 to VDDQ VVI/O Voltage on I/O Pins –0.5 to VDDQ +0.5 (≤ 2.4 V max.) VVIN Voltage on Other Input Pins –0.5 to VDDQ +0.5 (≤ 2.4 V max.) V

VTIN Input Voltage (TCK, TMS, TDI) –0.5 to VDDQ +0.5 (≤ 2.4 V max.) VIIN Input Current on Any Pin +/–100 mA dc

IOUT Output Current on Any I/O Pin +/–100 mA dcTJ Maximum Junction Temperature 125 °C

TSTG Storage Temperature –55 to 125 °C

Note: Permanent damage to the device may occur if the Absolute Maximum Ratings are exceeded. Operation should be restricted to Recommended Operating Conditions. Exposure to conditions exceeding the Recommended Operating Conditions, for an extended period of time, may affect reliability of this component.

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Under Recommended Operating Conditions…

• Consume IDD Max or Less• Meet or exceed all DC Parametric Specifications

• Input and Output Levels• Input and Output Impedances

• Meet or exceed all Timing Specifications• Cycle as fast or faster than specified• Capture signals within tS – tH windows• Produce Output Data Valid at specified time

• AND the population of devices will not exceed the forecast failure rate.

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• Burn-in forces “Infant Failures”

• Qualification Testing verifies Random Failure Rate over “Useful Life” (normally 10 years)

• Wear-out failures at “End of Useful Life” are normal.

Reliability

Drawing: http://en.wikipedia.org/wiki/File:Bathtub_curve.svg

10 Days 10 Years

50 FITSOr

Less

Useful Life

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Accelerating Failures

• Typical Burn-In Example• Abs Max Voltage & Abs Max Temp applied for 128

hours.

• HTOL* Reliability Test Example• Abs Max Voltage & Abs Max Temp applied to 315

devices for 1000 hours• 1 failure derates to 50 FITs over 10 Year Useful

Life* High Temperature Operating Life Test

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Summary

A population of devices used within Thermal

Recommended Operating Conditions and

Electrical Recommended Operating Conditions

will meet or exceed all specifications for 10

years while demonstrating a failure rate of no

more than 50 Failures per 1 Billion Device Hours

of operation (i.e. 50 FITs).