If an iPhone is properly stored and buried, what are the chances that the iPhone would still function 25,000 years later?

Answer by George Gonzalez:

Absolutely zero chance. 

The code stored in the flash memories would have long discharged.  Each bit is a small electrical charge bucket.   The charge is only guaranteed to hold for like 20 years.   Without software instructions and data the CPU in the phone has no instructions to follow, no way to boot up and start writing to the display and accessing the cell phone radio transmitter and receiver.

Also the semiconductors only work due to gradients in their impurity profiles.  Each transistor needs just a few atoms of plus or minus impurities in order to function.   But atoms diffuse, albeit slowly.   There are transistors that have been around for 50 years and a lot of them don't work so well anymore, partly due to diffusion.  After 100 years I suspect the crucial impurities will have diffused a few tens of microns, and the transistors will be considerably degraded, perhaps even to the point of not functioning.

The integrated circuits also depend on micron-thick conductive layers of aluminum, copper, and silicon nitride.   These could corrode and diffuse over time.  The IC's also depend on bond wires that are ultrasonically bonded to copper or aluminum pads.  These interfaces of dissimilar metals diffuse into each other, noticeable in just a few years, and the metal amalgams created are somewhat unstable.   The early IC's had big trouble due to the "purple plague":
Gold-aluminium intermetallic

And that happened in just a few months.  Nobody knows what these interface regions will be like in 100 years. 

The LCD screen depends on some very tricky crystal liquid compounds and on LEDs for the backlight.   These only have lifetimes in the tens of years.  The white LEDs depend on white phosphors which slowly degrade with use.  They also depend on trace amounts of rare elements and the LED efficiency might drop a lot as these elements diffuse around.

Also the electrolytic capacitors will be bad.  They generally use a semi-liquid electrolyte, which will eventually evaporate and diffuse through the seals and case.  Most electrolytics are rated at like 8,000 hours at 85 degrees C.  Aluminum Capacitors | Capacitors | DigiKey .That's not even one year.  At room temperature they will probably last 20 years but not a lot more than that.   Tantalum capacitors are known for suddenly shorting out at random.

The resistors in the analog circuits will have drifted out of limits.   You can expect up to 1% drift per year in your typical carbon resistors. Page on vishay.com  Most of the circuitry can tolerate a 20% drift, but after that performance will start to degrade.

The plastic parts may have warped or deteriorated to some extent.  Many rubbers and plastics depend on plasticizers to make them somewhat flexible.   The plasticizers can degrade or evaporate over time, leaving them hard or brittle.

All the adhesives will have dried up, evaporated, or crumbled to dust.

And of course the battery will be dead.

You could extend its life by keeping at near absolute zero, but its probably not designed for that, there would be huge stresses and stuff like solder and adhesives might fail.  Solder is almost pure Tin these days, and that undergoes a phase change at low temps, often crumbling to dust, so cooling it is a big problem too.

So just enjoy your phone, just don't use it while driving, and don't expect it to last forever.

If an iPhone is properly stored and buried, what are the chances that the iPhone would still function 25,000 years later?

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