The Importance of PCB in Automotive Electronics Reliability Design

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

Time and cost pressure

Like all products under pressure from design time and development costs, automotive components are no exception. One development practice that can greatly help electronics companies meet these basic business goals is to use virtual prototyping to analyze designs without the expense and time of building multiple physical prototypes, testing those models, and making decisions based on the test results. Make incremental changes. In addition, many factors that affect product reliability require weeks, months, or years of physical damage to be discovered. Therefore physical prototyping is not the way to go in these cases. Even in an experimental chamber, you can’t exactly replicate years of physical oscillations, thermal environments, vibrations and temperature cycling damage.

Simulation is key

Simulation, or virtual prototyping, has become an increasingly important step in the design process. As mentioned earlier, simulation not only saves time and money during the development process, but also simulates the longer-term effects of abuse in the harsh automotive environment. Just like Mentor Electronics’ Expedition Enterprise, a complex PCB system design solution contains multiple forms of virtual prototyping capabilities, including:

●Analog and digital signal integrity analysis

●Electromagnetic interference

●Thermal management

●Power integrity

●Oscillation and vibration

●Manufacturing design

One convention that takes advantage of all these features is that a good designer will use them throughout the design process, rather than waiting until the end (Figure 1). Waiting until the end of the process to incorporate these simulation results into a redesign wastes time and energy and is prone to compromise. Integrating good virtual prototyping into the design process can lead to over-design (i.e. the adoption of extremely conservative design methods), but often the result is increased product cost and loss of performance without ensuring continued reliability. Let’s look at three examples of good virtual prototyping practices during product development.

thermal control

The most critical factor affecting reliability (here in terms of performance) is heat. Problems can arise over time when integrated circuits (ICs) overheat, and the automotive environment can become very unforgiving. For example, overheating components in the engine bay, or driving through climates that range from Michigan winters to Arizona summers. Starting from the IC package, running through the PCB, and ending with the complete product in the operating environment, heat should be controlled. So we need to consistently employ virtual prototyping capabilities at all stages of design to ensure we have a thermally reliable product.

First, IC suppliers usually analyze component packaging and provide thermal characteristic models. Then we hope to analyze the stand-alone PCB as the design unfolds. PCB designers often need to analyze the layout of their working components to determine if they have created a board that is difficult to cool. And this work does not just roughly consider the heat dissipation and location distribution of the devices on the board. Since there are many heat dissipation paths (heat sink, inner layer copper of the circuit board, transfer, conduction and divergence…), the data transferred from the PCB design system to the thermal analysis must be complete. The analysis software must also be fairly intuitive to set up and execute, since you want the PCB designer using the software to not necessarily be a thermal expert and not delay the design process.

But the final virtual prototype must be executed under expected automotive conditions on single or multiple PCBs inside the final product enclosure. This kind of analysis is common in the field of mechanical design where a typical mechanical computer-aided design (MCAD) system has a complete physical definition of the product, including the enclosure, mounting method, heat sink and heat rail, and PCB. The PCB designer must pass the PCB design data to the mechanical designer for them to embed into the enclosure. The MCAD system needs to have complete 3D physical definition and thermal characteristics of the components and their leads, as well as all components of the complete product. Mechanical designers then use software like Mentor Graphics’ FloTHERM, which uses computational fluid dynamics combined with convection, radiation and heat transfer analysis to determine whether the IC exceeds critical temperatures and could cause reliability or performance issues.

FloTHERM has now been expanded to not only determine IC junction temperature, but also provide designers with guidance on what may be causing the problem and how to fix it. The software identifies “thermal bottlenecks” to show which parts of the heat flow path are restricted. Designers can use this information to identify alternative component mounting techniques and better heat conduction paths from the PCB to the case to alleviate bottlenecks.

Another valuable practice is to identify “thermal shortcuts”, which can point to potential design solutions that can speed up heat dissipation. The example in Figure 2 shows the original problem with a high-heat IC and the identification of shortcuts to solve the problem. In this case, adding padding between the IC and the case can create a more direct ambient heat transfer path. This simple change can reduce IC temperature by 74%.

Using sophisticated 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 arrive at better-performing solutions.

Highly accelerated life testing

Another cause of vehicle reliability issues is persistent PCB vibration and subsequent failure of component leads and accessories. Failures can generally be detected by building prototypes and placing them in an acceleration chamber, subjecting the PCB to vibration and temperature cycling. This approach requires building multiple prototypes as the design progresses, and it often takes weeks or even months to complete simulations of the expected life of the vehicle components in an acceleration chamber. This is a very time-consuming and expensive process, so reliability enhancement testing may not be complete and comprehensive.

There is currently software that can perform the same testing in virtual prototyping mode. Designers can use this software to define PCBs and easily conduct loss simulation experiments. The software can complete complex analyzes within a few hours and indicate possible failures (Figure 3). These failures can be corrected and the simulation rerun in a new version of the design. This iterative process leads to a suitable reliability solution quickly. The Israeli Ministry of Defense had early success deploying the software on their new generation combat vehicles. If the software can analyze possible failures in the extreme environment of a combat vehicle, then I will trust it in my car.

Power integrity analysis ensures high reliability

Power integrity is an increasingly complex issue in electronic product design. A few years ago, all ICs operated on 5V, and all you needed was a 5V power supply and ground plane to provide sufficient and stable power to the components. Today, ICs can operate in multiple voltage modes, down to 0.9 volts. Therefore, a single printed circuit board requires multiple complex distribution grids to provide these voltages and grounds. To save costs, computer-aided designers have to put these multiple distribution networks (PDNs) into as few ground planes as possible. The result may be a distribution network like Figure 4, with very tight internal space (neck relief) but the need to supply high levels of current to the IC.

Tight spaces can lead to serious reliability issues that may not become apparent for years. Excessive current will cause the space temperature to rise, causing the PCB to burn out or burst like a fuse. These distribution networks 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 solve this problem while maintaining sufficient current supply to the IC.

It is not practical to test the current density issue in a test room using physical prototypes because it may take several years before a failure occurs. The problem may never manifest itself, leading to subsequent failures in this area.

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Automotive PCB design and attribute attention nodes

Improving the autonomous performance of automotive applications covers three aspects:

1. Improve the environment: save fuel, reduce exhaust gas, and convert from gasoline and natural gas to hybrid and pure power. Therefore, electric vehicles have become a strategic direction of the automobile industry.

2. Improvement in safety: lies in the reduction of traffic accidents, from airbags, radar surveillance, plane cameras, infrared surveillance and automatic evasion to autonomous driving. Self-driving cars are currently absorbing most of the attention and investment.

3. For convenience and humanization: Convenience and comfort generally include audio, video display, air conditioning, computers, communications, Internet, navigation and electronic toll collection systems.

PCBs (Printed Circuit Boards) used in automobiles must also meet the above requirements.

Basic requirements for automotive PCB

Quality Assurance Request

The basic requirement for long-term quality assurance for manufacturers or distributors lies in the quality management system. Due to the particularity of the automobile industry, three leading automobile manufacturers from North America jointly established a quality management system specifically for the automobile industry in 1994.

As a technical regulation for the global automotive industry, ISO/TS16949 integrates the special requirements of the automotive industry and focuses on defect prevention, quality stability and waste reduction in the automotive parts supply chain.

Therefore, before entering the automotive market, automotive PCB manufacturers must first obtain ISO/TS16949 certification.

Fundamental request for performance

1. High reliability

The reliability of a car mainly comes from two aspects: on the one hand, the normal working life of the control unit and electronic components, and on the other hand, the resistance to the environment, which enables the car control unit and electronic components to have excellent performance in extreme environments .

The average service life of a car is 10 to 12 years, during which only parts or vulnerable parts can be replaced. In other words, electronic systems and PCBs must have the same service life as cars.

Vehicles are often affected by climate and environment during use, ranging from severe cold, extreme heat, and long periods of exposure to sunlight and rain. In addition, due to the working electronic components and systems, they must also accept the influence of environmental changes caused by heat. The same goes for automotive electronic systems and PCBs. Automotive electronic systems must overcome harsh conditions in the environment, including temperature, humidity, rain, acid fumes, vibration, electromagnetic interference (EMI) and electrical surges.

2.Light weight and miniaturization

Lightweighting and miniaturization contribute to fuel savings, resulting from the lightweighting and miniaturization of each component and circuit board. For example, the volume of automotive ECUs (electronic control units) was 1200 cm3 at the beginning of the 21st century and has been shrunk at least four times. The lightweight and miniaturization of PCBs stem from the advancement of density, reduction of area, reduction of thickness and multi-layering.

Automotive PCB performance

Various types

As a combination of mechanical and electronic equipment, modern vehicle technology blends traditional techniques with the latest science and technology. Different parts depend on electronic devices with different functions, resulting in the use of PCBs with different tasks.

Based on the differences in automotive PCB substrate materials, they can be divided into quadcopter ceramic-based PCBs and organic resin-based PCBs. The leading characteristics of ceramic-based PCBs are high heat resistance and excellent dimensional stability, making them suitable for engine systems in high-temperature environments. However, ceramic-based PCBs have poor manufacturability, resulting in high circuit board costs. With the development of newly developed resin substrates with higher heat resistance, resin-based PCBs are mostly used in most modern vehicles.

Follow a general rule: PCBs with substrate materials with different properties are applied to different parts of the vehicle to fulfill different functions. The table below illustrates PCB types that are compatible with certain vehicle equipment or instruments.

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in conclusion

Reliability is very important in automotive electronics, and today, given the pressure from time-to-market and cost reductions, it is increasingly necessary to conduct analysis in a software virtual prototyping environment versus a physical prototype in a test room. Currently, due to the existence of software, electronic and mechanical designers can carry out more simulation solutions.

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