PCB Reliability in Automobile Applications

1. Introduction and Background

　　Automotive electronics are not all that different from other complex electronics: multiple CPUs, networking, real-time data collection, and extremely complex PCBs. The design pressures in the automotive industry are similar to those in other types of electronics: short design times and fierce market competition. So what is the difference between automotive electronics and, for example, some high-end entertainment product electronics? A world of difference! If a PCB fails in an entertainment product, people's lives are not threatened; but if it fails in a car, people's lives are at risk. Therefore, the reliability design of automotive electronic components is a major aspect that needs to be considered during the design process.

　　2. The main points and outline of the full text are as follows:

　　a. Time and cost pressure

　　Like all products, automotive components are subject to design time and development expense pressures. One development practice that can greatly help electronics companies meet these basic business goals is the use of virtual prototyping to analyze designs without the expense and time of building multiple physical prototypes, testing those models, and making incremental changes based on the test results. In addition, many factors that affect product reliability require weeks, months, or years of physical damage to discover. Therefore, physical prototyping in these situations is not a viable option. Even in a test chamber, you cannot accurately replicate years of physical vibration, thermal environment, shock, and temperature cycling damage.

　　b. Simulation is the key

　　Simulation, or virtual prototyping, has become an increasingly important step in the design process. Like Mencius Electronics' Expedition Enterprise, a complex PCB system design solution contains various forms of virtual prototyping capabilities.

　　Figure 1 – Virtual prototyping should be used throughout the design process to reduce cycle time and costs and produce a reliable product.

　　c. Thermal control

　　The most critical factor affecting reliability (in this case, performance) is heat. Overheating of integrated circuits (ICs) can cause problems over time, and the automotive environment can be very unforgiving. For example, overheating components in the engine compartment, or driving through a climate that goes from Michigan winter to Arizona summer. Starting with the IC package, through the PCB, and into the complete product in the operating environment, heat should be managed.

　　Figure 2 – Identifying thermal shortcuts can lead designers to make changes that can make a big difference in heat dissipation.

　　Using complex thermal analysis in PCB design and mechanical design can lead to better thermal management and reliability without the need to build and test multiple physical prototypes. This saves a lot of time and money. In addition, with easy-to-use software that is tightly integrated with the design system, designers can quickly experiment with multiple "what-if" scenarios and obtain better performance solutions.

　　d. Highly Accelerated Life Test

　　Another cause of reliability issues in vehicles is the continued vibration of PCBs and the subsequent failure of component leads and attachments. This is typically accomplished by building prototypes and placing them in an accelerated chamber to subject the PCBs to vibration and temperature cycling tests to detect failures. This approach requires building multiple prototypes as the design progresses, and it often takes weeks or even months to complete the simulation of the expected life of the automotive parts in the accelerated chamber. This is a very time-consuming and expensive process, and reliability enhancement testing may not be complete and comprehensive.

　　Software is available that can perform the same tests in virtual prototyping mode. Designers can use this software to define the PCB and easily perform loss simulation experiments. The software can complete complex analysis in a few hours and point out possible failures (Figure 3).

　　Figure 3: Mentor’s HALT software can complete vibration, shock, and temperature cycling failure analysis in a matter of hours, compared to the weeks or months it would take in a test chamber.

　　e. Power integrity analysis ensures high reliability

　　Power integrity is an increasingly complex issue in electronic product design.

　　Figure 4: Mentor’s HyperLynx power integrity analysis identifies high-level current density headroom and potential long-term PCB failures

　　Narrow spaces can lead to serious reliability issues that may not show up until years later. Excessive current can heat up the space, causing the PCB to burn out like a fuse or explode. These distribution grids can now be analyzed in software, and virtual prototypes and high-level current density spaces can be identified. Designers can then expand the space or create parallel current paths on adjacent layers to address this issue while maintaining adequate current supply for the IC.

　　It is not practical to test for current density issues in a test room using a physical prototype because it may not cause a failure until years later. The problem may never manifest itself, leading to subsequent failures in this area.

　　3. Research report summary

　　Reliability is very important in automotive electronics, and now, given the pressure from time to market and cost reduction, it is increasingly necessary to analyze in a software virtual prototype environment as opposed to a physical prototype in a test room. Software now exists to enable electronic and mechanical designers to perform more simulation solutions.