Use Thermal Analysis And Other Types Of Simulation To Craft A “Cool” Design

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Fig 1. This image shows the temperature distribution on the top surface of a USB memory stick PCB.

Fig 2. Shown is an isolated
view of thermal bottleneck distribution in the top layer of the memory stick PCB shown in Figure 1. White and yellow areas indicate where heat flows are most constrained.

Fig 3. Shown is a typical neck-down area on a power distribution net. The net in this view is color-graded by current density.

Fig 4. A large heatsink in a power amplifier module can mechanically stress the board and its connections.

The primary function of thermal analysis is to predict the temperatures of components and parts within a product. By visualizing these temperatures, heat fluxes, thermal bottlenecks, and missed shortcut opportunities, it seeks to eliminate any detected thermal compliance issues.

These temperature predictions are important to other analysis disciplines as well, as many real-world engineering materials are known to have temperature-dependent thermo-physical properties. For example, copper’s impedance increases with increased temperature even within common design temperature ranges. Temperature effects can therefore be critically important to the electrical design, especially for power distribution, signal integrity, and timing signals considerations

Moreover, there may be tradeoffs when deciding what is good for thermal performance and what is good for the rest of the design. Thermal analysis results, then, can influence other forms of analysis by forcing design tradeoffs and compromises.

Thermal Analysis Moves Ahead

For the past 20 years, computational fluid dynamics (CFD) techniques have provided 3D conjugate thermal simulation results that predict and display temperatures in and around electronic product designs. Thermal designers routinely use predicted temperatures to judge thermal compliance, simply by comparing the simulated temperatures to maximum rated operating temperatures.

If the operating temperature exceeds the maximum rated value, there will be at least a potential degradation in the performance of the packaged IC and at worst an unacceptable risk of thermo-mechanical failure. These techniques are commonplace today, with widespread adoption all across the electronics sector including heavy usage in semiconductors, telecommunications, automotive, aerospace, and consumer products.

The typical means of visualizing the predicted temperature field for a printed-circuit board (PCB) provides useful information (Fig. 1). However, the latest advances in thermal simulation also offer the calculation and display of thermal bottlenecks and shortcut opportunities (Fig. 2). These offer insight into the reasons why certain temperature distributions occur and how best to resolve thermal issues.