Extreme heat, unavoidable moisture, and an exceptionally punishing environment are what passive components face when placed in the automotive world. With an environment notorious for its difficult conditions, miniaturized electronics are one of the last things one would think could handle such a setting.

Yet, with the aide of advanced materials and sophisticated technology, the same ceramic components found in common household appliances and high-tech gadgets can be adapted for use in today's automotive market.

Components designed for automotive environments face difficult conditions including heat, moisture, and punishing use.

One example is the changes made to common mode choke coils (CMCCs), also known as noise filters. Typically found in audio and video power supply circuits, cell phones, and other mobile devices, these passives provide noise control by removing unwanted transmissions without affecting high-speed signal waveforms. Due to changes in ceramic material and design however, CMCCs now thrive in an automotive environment and can be found in telematic features, navigation systems, air conditioning, automatic transmission and anti-lock braking systems (ABS).

Noise suppression is particularly important in automotive safety applications such as airbags. CMCCs minimize the noise between the airbag and the airbag deployment sensor providing an immediate connection without errors in between the system's modules.

Another component that has been adapted to suit automotive needs—specifically with regard to temperature thresholds—is the ceramic resonator (see below). As precision timing devices (at a basic function level), resonators offer high oscillation frequency and oscillation tolerance in integrated circuits and printed circuit boards in a variety of electronics. After altering resonators' temperature characteristics, they are now automotive grade and can be found in Controller Area Network (CAN) bus or any automotive network bus that requires tight tolerance such as airbag, engine, and body controls. Redesigning ceramic resonators for automotive grade components also gave automotive engineers an alternative to more expensive and larger quartz crystal resonators.

Automotive-grade ceramic resonators can be used instead of more expensive quartz crystal resonators in a variety of applications including engine and body controls.

An additional benefit to automotive grade ceramic resonators is their use in FlexRay technology. Touted as the next generation of CAN bus, FlexRay is currently being integrated into European made vehicles such as BMW. Deterministic FlexRay offers more advanced engine controls, higher data rates (10 megabits per second), redundancy, and fault-tolerance capabilities. It is expected to impact American automakers soon.

CMCCs are well suited for noise suppression problems and can also be placed in advanced FlexRay automotive applications.

Heat
There are several challenges when it comes to designing passives for automotive applications—the most significant being heat. Automotive grade components must operate flawlessly in a range of extreme temperatures from -40 to 125C degrees under the hood and up to 150C near the engine and transmission.

Originally, ceramic CMCCs made with a ferrite core, did not fair well in the brutal high temperatures. However, by improving the ferrite materials through changes in the composition of the ceramic, CMCCs now have high enough magnetic permeability (μ) at higher temperatures and have become ideal for use in these applications as a result.

Previously, ceramic resonators' main limitation was also the heat factor. They were unable to maintain their precision in higher temperatures making them unsuitable for the automotive market. With another composition change in the piezoelectric (PZT) ceramic and precisely controlled manufacturing process however, resonators now operate effectively up to 150C.

Heat is a factor not only in standard vehicles, but in the increasingly popular hybrid cars as well. According to a study published in October 2006 by the Freedonia Group, the demand for hybrid electric vehicles will grow annually by 20% through 2010. While hybrids do not get as warm under the hood, their electric power components still must meet automotive grade standards. Given that, the need for electronics that can withstand high temperatures will increase exponentially in the future.

Another hurdle that components have to overcome before they are placed in vehicles is the reliability issue. Currently, there is no worldwide standard for automotive grade reliability. In the United States, AEC-Q200 was established by the Big Three automakers to define common electrical component qualification requirements, testing methods and guidelines. However, Japan and Europe use different testing benchmarks. For example, while all vehicle makers need components to pass a stringent heat cycle test, the temperature as well as the minimum number of cycles needed to achieve automotive grade vary considerably. As a result, electrical components must be custom made according to each manufacturer's specifications

At Murata Electronics, engineers created an internal reliability specification to satisfy the differing demands. This helps reduce cost and assures that all ceramic components destined for vehicles meet the variety of automotive grade standards.

Moisture
Exposure to rain, snow, salt, and humidity can damage various parts of a car or truck—electronic components included—so car makers take numerous steps to prevent it. For example, many manufacturers place a protective coating on printed circuit boards. This coating however, can enter into the casing of a conventional CMCC because of a slit in the packaging. Once the coating compromises the CMCC, the wire interior can "escape" due to the temperature expansion differences between the coating and the CMCC body. To prevent this, automotive grade CMCCs are made without the slit. In order to achieve this advanced design, a new manufacturing machine was invented.

Mechanical strength
A typical consumer-electronics component is generally not subject to the constant stress and use seen by automotive electronics. Endurance becomes an important factor and, without adaptations, passives cannot handle the abuse. However, electronic makers who invest heavily in research and development have created sophisticated methods that improve ceramic materials so that they can take the constant punishment and make automotive grade.

Using CMCCs again as an example, the ferrite core structure has been redesigned. Unlike the material changes needed to combat heat, the basic shape of the core itself was altered. Then, using an advanced stress evaluation computer simulation, the CMCC was tested and, through software analysis, deemed capable of proper function in a difficult automotive environment.

Outlook
Cars of the future will only increase their reliance on electronics and passive components. With the addition of sophisticated entertainment technology and advanced safety features, ceramics will continue to be in great demand. Requirements for automotive grade components may change again, but companies who use innovative materials, adaptable designs, and cost-effective production methods will have no trouble placing components aboard even the most complex vehicles.

Yuji Nakanishi is automotive manager for Murata Electronics North America.