this desk fan is 85 years old and still running strong. how would YOU design an electronics gadget to last 100 years? what components would you use? what potential failures would you expect?

bonus: how would you make it last 200 years? how about 500 years?

thanks for all the responses. i noticed some interesting patterns:
assume humans are around the whole time, so make it easy to repair. *lots* of subtlety to unpack on this one.
material choice is critical
keep it as simple as possible, but as complex as is needed.

honestly i didn't think of the repair thing even though it may seem obvious. i guess i was thinking about a device that could survive 200 years in a dusty closet. but repair is very important!

repair:
include all original design documentation. include design intent.
in 200 years, standard interchangeable parts could look *quite* different
materials and objects we think are stable/archival might change in surprising ways

bigger is better. if a tiny screw is no longer a standard off-the-shelf item in 200 years, someone's going to have to fab a replacement. big=easy
no *complex* potted/sealed modules. simple ones are ok if thoroughly documented (think of a transistor).

design to very wide tolerances (mechanical and electrical).
build 10 and make them modular to ease troubleshooting.

materials:
all chemicals react, but some react more slowly than others.
avoid electrolytic capacitors and batteries, with one exception*. they are wet chemistry experiments that eventually turn everything into a pile of white powder

the one exception is a battery that is missing a reactive component. https://en.wikipedia.org/wiki/Baghdad_Battery (controversial, i know, but it did last 2000 years or so)

a lot of people have been asking about chips. it's mixed. if a chip is in a hermetic package with a nice thick gold plating then the limiting factor for age is actually diffusion (electromigration if it's continuously under power)

diffusion of the dopants. during manufacture, they're diffused at high temperatures, but motion doesn't cease when the temperature drops. it just happens very slowly. so thresholds will shift and eventually transistors won't transist anymore.

flash memory and EEPROM is right out. the bits are just electrons on a floating gate and they'll be gone due to quantum tunneling in a comparatively short time.

electromigration happens when there's an electric field or a flowing electric current in a powered-on device, making the metal ions move. move enough atoms, and now you don't have a trace anymore.

still thinking about materials.
PCB materials are usually fiberglass (lasts a very long time) and resin (uhhhhhhhhhh)

ceramic is a much more stable material, but it can be broken. i guess if you build your circuit on a thick slab of patterned ceramic you'll be ok.

now, complexity
simple=good can be deceptive. something that is TOO simple can be worse. you want it to be just complex enough
reliability folks think about series vs. parallel systems. 2 parallel systems improve your reliability even though you have 2 things instead of 1

oh, something i forgot to mention
the storage and operating environment is important!

environment:
heat is bad. rapid, repeated temperature changes are bad
moisture is bad
oxygen is bad
sunlight is bad (UV radiation)
living things gotta eat. bacteria, mold, plants, small rodents--all of them want to chow down on your gadget

ionizing radiation will also be hard on your gadget.

wind (typically coupled with fine particulates)
vibration and repeated mechanical movement

honestly the best way to ensure your gadget will survive more than a few hundred years (in addition to all of the above) is to enlist a 24/7 maintenance crew to keep it clean, polished, repaired, and to maintain the documentation.

so how do you enlist a team of dedicated volunteers who will do all of this for you for free? (since economies will come and go, countries will split and combine, wars will be fought...)

easy! just start a religion around it.

so let's look at a few examples of electronics and see how they measure up. to start, this is a ceramic circuit board that goes down an oil well (probably in a drill bit)

it's got gold plating, nothing organic, no resins (the die attach could be silver solder?). it can handle 200C for thousands of hours, no problem.

only problem: it's impossible to repair without specialized equipment.

here's an oscilloscope (actually an oscillograph) from 1935.
it's simple, easy to repair, can handle wide component tolerances. what's wrong with it?

there's mold growing on the resistors, for one thing. also, all the metals are beginning to corrode. and the paper capacitors have all failed.

too many organic materials.

ok how about this module from an analog synthesizer?
chips in plastic packages
electrolytic capacitors
resins
actually it's terrible, but for one thing
team of dedicated volunteers who maintain it for free (aka a religion, aka modular synth fanatics)

ok, i'm joking a bit about the last one

but only a little

then of course there's this famous thing
bronze corrodes
bad environment: kept in salt water for 2000 years

and yet it still survives. i wonder how many others like it existed, and where they are now. probably scrapped for parts?

that last one is the Antikythera mechanism.( https://en.wikipedia.org/wiki/Antikythera_mechanism)

i guess if the gadget is inaccessible to most people, then they can't steal it for parts, smash it, or otherwise damage it. inaccessible can be based on location...

... or the team of dedicated volunteers guarding it 24/7