Among the primary concerns of an airline pilot are getting passengers to their destination safely and on time, and knowing that all systems are operating properly. In the recent design of a new plane, consideration was given to reducing one of the reasons for departure delays - a burned out incandescent bulb in the cockpit instruments. Most major aircraft manufacturers use incandescent bulbs integrated into cockpit switches to indicate on/off functions and to act as alarm indicators for non-functioning systems . Zenith Microcircuits, a subsidiary of Zenith Electronics Corporation, teamed up with DuPont Microcircuit Materials to provide the solution.
Recent advances in light-emitting diodes (LEDs), coupled with their reputation for reliability and long life, made LEDs an excellent candidate for this task, provided that a suitable electronic power source could be found to illuminate the diodes. An important constraint was that the driver electronics and the diodes would have to fit into existing cockpit switch housings. Small size, as well as reliability and durability, would be necessary to meet the challenge.
Zenith used DuPont thick film conductor and resistor materials to design and build two separate hybrid circuits for the new LED cockpit switch. One ceramic substrate, patterned with DuPont thick film conductor materials, serves as the base for mounting an array of diodes for the light source, while a second ceramic substrate, printed with DuPont Ag-Pd and gold conductors and thick film resistors, forms the basis for the driver circuit. The thick film conductors proved compatible with both the epoxy and solder attach materials used to assemble the components. This allowed the electronic driver circuit and LED array to meet the size requirements for fitting into the switch housing.
The use of high-thermal-conductivity alumina substrates also made it possible to design circuits that could operate over the temperature range necessary for the application. Because of the heat generated by the diodes and the closed environment of the switch housing, the conductor materials had to exhibit excellent adhesion, for reliable operation over the circuits' expected lifespan of 14 years. DuPont thick film conductor and resistor materials printed onto ceramic offered the adhesion and stability needed for long-term, dependable use.
As a result of this success, it is expected that light-emitting diodes incorporating DuPont ceramic interconnect materials will continue to be used as illuminating devices in cockpit switch assemblies, thus helping to keep planes in the air and ensure their on-time arrival.
For more information, call DuPont at 1-800-284-3382, press 3.
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