Those poor passives — being what they are, they often don't get the consideration and respect they deserve. It's easy to worry about the performance and reliability of semiconductors for rugged designs at temperature and vibration extremes, but passives can easily be overlooked. After all, what can go wrong with a resistor or inductor, compared to an IC?
Lots of things can go wrong. First, consider the number of passives associated with analog circuitry. My experience and anecdotal evidence show that a digital part of a circuit typically has two passives per IC (usually bypass capacitors). The analog circuit spanning DC through RF (plus power supply) usually has at least five and often up to 10 passives per IC. Further, these are usually a mix of capacitors, resistors, and inductors, plus specialty devices such as circuit-protection components.
Of course, what's extreme depends on the situation. We most frequently think about operation at high temperatures and sometimes low temperatures as the problem, but there are other things to worry about. Vibration is second to temperature, because it can fracture connections and internal structural elements.
But, wait, there's more, as those low-budget infomercials say. Some designs are challenged by truly unique conditions. Consider Coilcraft's recently announced AE425PJB inductor series. Not only do these passives have a suspended core design to pass 80g vibration testing/1,000g shock testing and operate at up to 155°C, but they also are compliant with NASA’s low-outgassing specifications, which are critical for operating in the vacuum environment of space.
Some applications are at the opposite end of the atmospheric spectrum. Vishay makes thick-film resistors, such as its RCWP series, that are highly resistant to sulfur-laden environments. You might expect such conditions in harsh applications such as mining, but they also exist near automotive exhaust systems.
Let's give those passives — resistors, inductors, capacitors, connectors, wire/cabling, and others — their due respect, considering the vital role they play in all circuits, especially analog ones. Perhaps they finally are getting some of the recognition they deserve: the European Space Agency recently held the first International Symposium on the subject, Space Passive Component Days.
What sort of extreme design challenges have you faced? Did you use a component-by-component approach, or did you just put the whole thing in a box and try to protect the complete assembly?