In 1977, the average automobile contained $110 worth of electronics. By 2003, the electronics content was $1,510 per vehicle. This is expected to reach $2,285 by 2013. The turning point in automotive electronics was government regulation in the 1970s, mandating emissions control and fuel economy. The complex fuel control required could not be accomplished using traditional mechanical systems. These government regulations, coupled with increasing semiconductor-computing power at decreasing cost, led to an increasing array of automotive electronics. The increased electrical power requirements in automotive systems spurred the push to 42V systems, which are now beginning to be used.
The operating temperature of the electronics is a function of location, power dissipation by the electronics and the thermal design. The automotive electronics industry defines high-temperature electronics as electronics operating above 125°C. The underhood automotive environment is harsh and current trends in the automotive electronics industry will be pushing the temperature envelope for electronic components. The desire to place engine control units on the engine and transmission control units either on or in the transmission will push the ambient temperature above 125°C. However, extreme cost pressures, increasing reliability demands (10 years/150,000 miles) and the cost of field failures (recalls, liability, customer loyalty) will make the shift to higher temperatures incremental. The coolest spots on engine or in transmission will be used first. These large metal bodies provide considerable heat sinking to reduce temperature rise caused by power dissipation in the control unit.
Table 1. The five major categories of automotive electronics.
The transition to X-by-wire technology, replacing mechanical and hydraulic systems with electromechanical systems, will require more power electronics. Integration of power transistors and smart power devices into the electromechanical actuator will require power devices to operate at 175 to 200°C. Hybrid electric vehicles and fuel cell vehicles will also drive the demand for higher-temperature power electronics. In the case of hybrid electric and fuel cell vehicles, the high temperature will result from power dissipation, not ambient conditions. The alternates to high-temperature devices are thermal management systems, which add weight and cost.
The number of sensors in vehicles is increasing as more electrically controlled systems are added. Many of these sensors must work in high temperature environments. The harshest applications are exhaust gas sensors and cylinder pressure or combustion sensors.
DaimlerChrysler, Eaton Corp. and Auburn University jointly published a summary of automotive high-temperature requirements (Table 2). The current DaimlerChrysler on-engine temperature specification is -40 to +165°C, and the in-transmission specification is -40 to +150°C.
Table 2. Mechatronic maximum temperature ranges.
While electronics are expected to survive high-temperature exposure, it is not necessary for them to survive for thousands of hours at the maximum temperature.
Device and packaging technologies for high-temperature automotive electronics provide an exciting area for development during the next decade.
R. WAYNE JOHNSON may be contacted at Auburn University, 162 Broun Hall/ECE Dept., Auburn, AL 36849; (334) 844-1880; [email protected].