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64 The PCB Design Magazine • December 2015 ic interference (EMI), power integrity (PI) and thermal integrity (TI). The Automotive Electrical System Figure 2 shows an abstract view of an auto- motive electrical system with a few of the major subsystems included. A single electronic control unit (ECU) is labeled in the figure. This master ECU is supported hierarchically by ECUs with local control over their respective subsystem components. Past generations of automotive ECUs were typically simple two-layer PCBs, even for the master ECU. PCB physical design (e.g., layout) was accomplished with general drafting tools and SI/PI/TI/EMI simulations were not of- ten required. For modern automotive systems, the lowest-level ECUs still typically have small, two-layer PCBs, but a modern master ECU fea- tures a complex, multilayer PCB. Subsystem ECUs might also be quite complex; this is the case for an infotainment system that includes multiple high-definition displays, high-defini- tion audio and broadband Internet connectiv- ity. The main ECU integrated circuit is typically called a microcontroller. It has become a com- plex, high-pin-count, high-speed, multicore processor and is anything but "micro." Some automotive electrical systems have grown to have as many as 100 ECUs, which im- plies a very complex system. There is a trend to reduce this large number of ECUs by a factor of two to three. The trend is toward more complex ECUs at the top of each hierarchical subsys- tem with smart sensors at the lowest level. This trend implies more complex PCBs for each sub- system high-level ECU and potentially no PCB for some of the local sensors. As automotive system components, the master and high-lev- el subsystem ECUs must be absolutely reliable and low cost. Their PCBs must support higher Figure 2: Automotive electrical system. article ELECTRICAL DESIGN CHALLENGES FoR AUToMoTIVE PCBS