This series of articles explores thermal and stress analysis for electronic assemblies — no matter where they are used: cell phones, cameras, computers, avionics, missile and defense systems, or high-power applications.
Electronics face demanding environments. A few of the key analyses and tests they must tolerate include:
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🔥 Temperature
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💥 Shock
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📳 Vibration
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🌡️ Thermal stress
While small, low-power components (like resistors) usually dissipate heat quickly and pose fewer challenges, high-power components require careful analysis and testing.
Conduction Paths
Several circuit card assembly details affect how heat flows:
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Number of layers
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Circuit card material
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Copper thickness
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Percentage of copper on each layer
Solder joints provide excellent heat conduction to terminals. Many components also use heat sinks or thermal pads to improve heat transfer into the board and eventually out to the atmosphere.
Altitude Effects
Altitude has a major impact on electronics cooling:
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Air temperature drops at higher altitudes.
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Air density also drops, reducing convective cooling.
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Radiation becomes a much more dominant cooling mechanism.
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Conduction remains largely unaffected.
Designers must account for this shift in heat transfer mechanisms, especially in aerospace and defense applications.
Heat Flow Paths Out of Circuit Card Assemblies
Conduction is usually the best way to remove heat, but it’s not the only path. Heat flows through:
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The circuit card to the assembly case
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From the case to external structures
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Finally, out to the environment through convection or radiation
A robust thermal design considers every stage of this pathway.
Lessons from Compact Fluorescent Light Bulbs
Compact fluorescent bulbs were once marketed with lifespans of 10 years. In practice, many fail in 1–2 years. Why? Likely heat.
The electronics in the bulb’s base operate in a hot, confined space. Over time:
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Elevated temperatures shorten component lifespans.
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Thermal cycling leads to expansion and contraction.
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Solder joints can fail due to mismatched thermal expansion between the board, solder, and components.
This is a small but clear example of why thermal and stress analysis matters in electronics.
Next in the Series: Component Specifications
The next article will look at component specifications — and how real-world conditions often push them far beyond their rated limits.
Norman T. Neher, P.E.
Analytical Engineering Services, Inc.
Elko New Market, MN
www.aesmn.org