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54 The PCB Design Magazine • September 2016 by Gabriel Ciobanu CONTINENTAL CORPORATION and Boris Marovic MENTOR GRAPHICS Continental 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 com- pany supplies to OEM and other manufactur- ers 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 re- sistance for heat, outside the IC package, is the PCB. Continental engineers use 3D computa- tional fluid dynamics (CFD) to simulate and test a PCB's thermal design (Figure 1). 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 con- vection, conduction, or radiation. Knowing the thermal junction resistance allows optimizing a design for more efficient and less costly heat- sinks, materials, and ICs. When building a model to use in simula- tion, different methods can be used to represent chip packages and PCBs. Chip packages are typi- cally defined as four types (Figure 1). The simple cuboid is a lumped component with some ma- terial properties and a heat source applied to it. The 2-resistor model doesn't include any ther- mal capacitance and is therefore not suitable for transient analysis of component temperatures. The Delphi model is comprised of several ther- mal resistances and capacitances and thus is more accurate and suitable for transient simu- The Fundamentals of Improving PCB Thermal Design ARTICLE