The Fundamentals of Improving PCB Thermal Design

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Continental's automobile engineers have many years of experience building critical parts and systems for automobiles, from the chassis and safety systems to the powertrain, interior control systems, and tires. Much has changed in the past decade, and electronic technology has become an important aspect of what the company supplies to OEM and other manufacturers worldwide. Electronics are doing more now than ever to provide safer cars, cleaner power, more mobility, and smarter driving.

Making sure that automotive electronics are reliable, safe, and properly designed begins at the component level. Heat must be addressed early in the design process for these goals to be achieved. The most important thermal resistance for heat, outside the IC package, is the PCB. Continental engineers use 3D computational fluid dynamics (CFD) to simulate and test a PCB’s thermal design. Modeling the main heat flow paths in detail is critical to ensure that generated heat in the component flows out to the ambient, either through convection, conduction, or radiation. Knowing the thermal junction resistance allows optimizing a design for more efficient and less costly heatsinks, materials, and ICs.

When building a model to use in simulation, different methods can be used to represent chip packages and PCBs. Chip packages are typically defined as four types. The simple cuboid is a lumped component with some material properties and a heat source applied to it. The 2-resistor model doesn’t include any thermal capacitance and is therefore not suitable for transient analysis of component temperatures. The Delphi model is comprised of several thermal resistances and capacitances and thus is more accurate and suitable for transient simulations. Finally, the detailed model is modeled explicitly and is the most accurate model; however, it also increases the simulation time and requirements for computing resources.

For the PCB, four detailing levels from simple to complex also are used in simulation: lumped approximation, individual layers’ representation, layers modeled with “patches,” and copper tracks and areas modeled in detail.

To read this entire article, which appeared in the September 2016 issue of The PCB Design Magazine, click here.


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