[ref]sars[/ref], I'm not able to give you a definite answer about the lifespan of semi-conductor components as there are simply too many factors that can affect that. However, I can give some of my thoughts on this in three categories of components that you can find in all our cars:
1. Digital component
For this type of component, if it's properly made and tested, I would expect them to last 10, or 20+ years. What's usually failed is the peripherals (e.g resistor, capasitor on the PCB or PCB itself). However, the yield rate from the foundry varies. The design of DFT within the chip varies. And the test pattern generated to test the chip also varies. Therefore, the variation of the lifespan is also quite big. This is as what [ref]pvr[/ref] said, for the same stuff (functional-wise), one brand sometime last much longer than others. However, for automotive grade component, I think they will last much longer than the rest of the car as long as it's working within the designed circumstances (like you said, temp, humidity etc.).
2. Flash memory
The lifespan of these type of components depends heavily on the number of erase cycles. Let's give a very brief example here. Assume the flash size is 16GB and your navi map is also 16GB, and each map update requires erasing all existing data then write new data in. In this case, you can expect some data errors after you update the map 1000-3000 times (if it's TLC type). Then, this is just an example. In reality, a lot things may need to write to the flash memory. The famous real example is the Flash memory issue in older Tesla. As the car logs so many things to the flash, many reports of the flash in the head unit failed after 3-5 years and need to be replaced.
3. Analogue device or devices involve analogue components
As you mentioned, many older cars suffer from faulty sensors. I usually categorise sensors as analogue devices. It measure certain parameters then translate/convert to another format (usually digital signals). My work doesn't involve analogue devices at all so I don't have too much experience to talk about the lifespan. However, what I've observed is that this type of device also last for a long time (10+ years) but with the age increase, its reading usually drifts a lot and can be affected by the environment a lot. From a vehicle control module's perspective, if certain sensor gives a reading outside the design tolerence, then we can consider it as a component failure.
