[Animats]

How do you build modern electronics for a 30-50 year lifespan? What parts do you use?

I happen to know that the Ford EEC-IV engine control module of the 1980s was designed for a 30-year lifespan. Which it delivered; many 1980s vehicles are still running with it. But newer electronics won't last that long. Line sizes are too small, and minor effects such as electromigration cause wear-out.