Supplier eBooks

CHARACteRiStiCS oF deviCeS deSigned FoR HARSH enviRonmentS One of the approaches device manufacturers have taken to mitigate the challenges offered by an automobile's harsh environment is to customize the processes used to fabricate semiconductor devices. Figure 2: Downhole logging instrumentation signal chain. 21 These custom processes can be modified to address key challenges, such as those presented by high temperatures. One of the challenges presented by high temperatures is increased substrate leakage current. Leakage current robs transistors of operating current, which at best increases power consumption and at worst can cause circuit failures. Advanced processing techniques can significantly reduce leakage current by constructing barriers to leakage current flow. One common approach is to use a silicon-on- insulator process, where an oxide insulation layer is placed below the transistor, or to add an isolation trench between transistors. work when the manufacturers specifications are exceeded. For example, it is relatively simple to test devices at extended temperatures in a test chamber to see how well they perform. This can be a fruitful approach when a specific device can provide a large benefit but is usually too costly and time-consuming for a wide array of devices. The second approach is to select devices that are manufactured specifically for the harsh conditions an automotive application will face —devices that are specifically manufactured for harsh environments will usually save the developer both time and money. In reviewing electronic devices' suitability for use in harsh automotive applications, a useful source for common qualification and testing standards is the Automotive Electronics Council, or AEC. These AEC standards (such as AEC- 100 for integrated circuits) are manufactured such that additional qualification and testing are not needed for use in the harsh automotive environment, as defined by the standard. Even when devices have been tested and qualified (either by the developer or the manufacturer) it is standard procedure to do additional testing at the board level. A test chamber or a complex software simulation can be used to duplicate harsh automotive environments. A prototype board can be subjected to temperature cycles, vibration and moisture while measurements are made of temperature gradients and package stress. Identifying major electronic hot spots can help determine proper device placement to minimize heat effects for sensitive devices. These measurements can help pinpoint devices that might require additional temperature or mechanical resilience. In automotive applications it's best to work through these issues in the lab instead of on the road.

• Cover