Let's say you wanted to preserve some electronics for 500 years or more in a museum. What could you do to preserve them in working order for hundreds of years? Deep freeze? Lead lined vaults? Vacuum? I've seen questions about how long electronics would last left unattended, but not how to proactively protect them for 500 years.
Let's say this is a fully functioning world, not a post-apocalyptic world. Think of a museum in the future.
You need purpose-built items, with specially designed components and maybe even ad hoc designs (PSUs without electrolytic capacitors, etc.), capable of withstanding extreme cold.
Otherwise, there are several chemo-physical processes that would require to be halted.
Most components aren't engineered to last at all, because the manufacturers know that the items will be replaced anyway inside, at most, of ten years. Just like ol' Henry Ford, who was said to send forensic teams in junkyards to tell him which parts of his cars had not failed so that he could start manufacturing them with cheaper tolerances. Only, this "controlled obsolescence" makes good business sense, and is actually done.
The five major things that can degrade electronics are electromagnetism, corrosion, excessive temperatures, vibration, and impact.
Electromagnetism is your number-one risk. It only takes a static shock with 1/2 the current it requires to make a visible spark to damage data; also, background EM radiation can degrade data slowly over time. Forensics investigators will often mitigate this risk by putting evidence into a static resistant evidence bag, which can then be placed in a Faraday bag essentially blocking out all external EM influence.
The second risk is corrosion. For a device that you are not regularly handling, the only major outside corrosive agents you need to worry about are humidity, and to a much smaller extent, oxygen. An air-tight evidence bag also works well for protecting against these; however, an off-the-shelf evidence bag may not be rated for 500 years. You would likely need to consult with a polymers expert to design such a container.
Excessive heat and cold become the hardest part to control over a 500 year gap. You can not exactly rely on an air conditioning system to be maintained for that long, but if you were to store your device in an underground bunker at a depth of at least 30 feet, mother nature will keep your temperature more or less constant at a temperature that is ideal for most electronics.
Vibration mostly just affects things with moving disk drives in them; so, for purposes of preservation, I'm assuming you are talking about stored and not actively used hardware; so, this should be a minimal issue. That said, if you are occasionally powering your device on, it is best to do so on a heavy well secured desk or shelf. Lighter desks/shelves can be vibrated by a computer's fans reducing a computer drive's expected life-time by up to 75%.
Last is impact. If you are storing this device in a room full of engineers going about their daily businesses, eventually someone will knock it off the shelf and break it; so, storing it in a place with very limited human access is also pretty important. This makes keeping an electronic device from breaking within 500 years almost impossible for something that you need to use, but if you're talking about purely storage, you should be able to do this and the above four steps and have a pretty good success rate at storing electronics for that long.
In response to the first edit:
If you are talking about a museum scenario, the mostly likely case would be to copy the data onto a replica, and then put the replica on display. Museums rarely put items that fragile and rare on display.
Locate your museum on a rocket that is accelerated up to a significant fraction of the speed of light, so that time dilation means that the device you're preserving will only experience a small fraction of the 500 years you're preserving it over.
Breaking the device down on a part-by-part basis, and looking at what would be involved in preserving them:
There's no way to preserve an electronic device for 500 years in a way that permits immediate re-powering at any time. A museum would, however, be able to preserve one that only requires relatively minor maintenance before using, and the techniques involved are ones that museums commonly employ.
If powered down, electronics can last as long as they don't take physical harm, with the exception of batteries and the bearings in moving parts like fans or platter hard drives.
Batteries, sad to say, can't be made to last that long -- or at least the kind that are useful for portable devices like tablets,. notebooks, and smart phones. There's a type of rechargeable battery that has been shown to last a century, and can likely last much longer than that -- the Edison iron battery -- but they have rather poor energy density. In English, that means a battery that can run a tablet for four or five hours continuously is closer in size to a car battery than the little lithium wafer cells our tablets have now.
Nothing would keep those devices from working on external power, however, so it might be worth storing dry-charged lead-acid batteries, which can last indefinitely before filling with acid.
In all honesty, electronics are incredibly difficult to preserve, due to the very nature of their components.
Particularly, batteries have a defined shelf life, even when unused. Capacitors and resistors (key components in most electronics) also have a limited lifespan, though they may degrade much more slowly if not in use. Storage media (such as flash memory or hard disks) have a limited life cycle related to the number of read/write operations performed. To have the electronics active, even just displaying a static screen, would likely severely limit the lifespan of any electronic device.
The solution for museum displays would necessarily be restoration/periodic repair. There would have to exist a manufacturing process to produce replacement parts for the duration of the displays existence in the museum.
Preserving electronics for 500 years in working order dictates that they not be used at all in that 500 years.
Copper, in particular, gets brittle as current passes through it and it heats up, and the copper traces in circuit boards even more so. The resistance of the copper joints also goes up.
Electromigration is also a problem.
Unfortunately, the only way you will know if they still work is to turn them on, but every time you turn them on, you increase the chances that next time they will not work.
Maybe you can?
LSemi gives a good list of the problems, but may be too pessimistic with "you can't".
Most of the problems can be arrested by cooling the device down close to absolute zero. In physics jargon, the decay processes are thermally activated. The question is whether you can get an electronic device down to that temperature without causing irreparable damage while cooling it or thawing it (exactly the same problem as with cryo-sleep for people in sublight starships).
Electronics is generally tougher than biology.
The obvious exception is data stored as packets of electrons in flash memory and similar. It relies on regularly being powered up so it can check for and repair any bit-rot while powered down. Charge will not leak away because of thermal effects close to absolute zero, but is still subject to corruption by radiation such as cosmic rays. This will accumulate with time, and reach a point where the data is irretrievably corrupted after thawing it out.
Some electrolytic capacitors contain a water-based electrolyte paste. If this expands as it freezes, the capacitor will be destroyed. Most quality motherboards these days advertise solid capacitors, which may be more freezable. The big capacitors in power supplies aren't of this type, though. Electrolytes in batteries, similar questions.
I'd guess that you can cryo-freeze and thaw motherboards, processors, SSDs and probably displays and hard drives (they can go well below freezing point without being destroyed, look at the minimum storage temperatures specified for military grade HDs). Petroleum lubricants do not expand on freezing. About liquid crystals in displays, I would hope that a thin film of liquid in a somewhat flexible container (poke your screen!) would freeze OK.
Freeze-thaw cycles will tend to cause soldered joints to fail, but here we are talking just about one big freeze and one thaw. The frequent heating and cooling of a computer turned on and off daily is probably more damaging.
A museum might well buy several of each item it wanted to preserve. One for display, which would become non-functional within decades. Others, for cryo-preservation, so at least one of each component has a good chance of survival. Power supplies and batteries have a simple specification (voltages and currents required, ATX or similar power button logic), so as long as technological civilisation persists, the simplest preservation answer is to reconstruct a power supply at the time one wanted to thaw and power up the preserved technology. If civilisation fails, so does cryo-preservation.
BTW This sounds like a fun bit of research for anyone with access to a very low temperature freezer or lots of liquid nitrogen.
As @Dave says, it makes sense for archival purposes to separate the physical object from its functionality.
Original manuscripts of Shakespeare plays still exist in libraries, but they are extremely fragile and essentially useless for their original purpose – if an actor tried to keep a dogeared copy rolled up in his doublet, it’d be reduced to dust before the first rehearsal. But the text of those plays is preserved perfectly, and a modern copy works just the same.
An iPad is similar. If you took out the battery and any large capacitors, you’d have a perfect record of what it was physically like to hold one, but to know how it worked, you’d be much better off with a copy of the source code. Bear in mind, the electronics will also exist in a purely digital form (the Verilog / VHDL / etc used to design the components and PCBs), which is, if anything, a more faithful record of how it’s supposed to work than the actual manufactured article.
You might say that a simulation isn’t “the real experience”, but everything in a museum is divorced from its original context anyway – if you had a working iPhone 500 years from now, you still wouldn’t get the authentic experience unless you simulated a 4G network, and Twitter and Facebook, and all their living users. The very act of preserving something in a museum changes it into something else.
The same applies to preserving technology through a future dark age – a working iPad isn’t much use, but a description of how it works could be much more useful.
How about an alternative? Instead of storing the physical device, store the designs of the device and all of its components. When you need a working item, you manufacture it. This is actually possible, though it isn't easy. There are three substantial challenges to it.
While all you are storing is data, storing data for long periods does have its challenges. The basic procedure of making copies frequently should work just fine.
Making electronic gadgets today involves a number of large, expensive factories. Making them in the future may be very expensive but it might be cheaper. And, it may be possible to create something with the same electrical or logical properties with newer techniques.
Gathering the data you want to store is much more difficult than simply getting your hands on the gadget. You would have to convince all of the manufacturers involved to part with information that they think is extremely valuable.
So, it may not be practical, but at least it isn't impossible.
I think the thing to do would be to separate the software and electronic function from the mechanical interaction. That is, you could have museum visitors hold and play with dead or dummy iPads that do not turn on, and separately interact with a virtual machine on a touch screen if they wanted to "use" it. This is more or less done today as I've seen multiple websites running vintage operating systems where you can relive the joys of Windows 95 or 3.1.
Virtual Reality
In addition to the (well-written) Answer "you cannot":
If it is not possible to stay the hardware in usable order for this time, you could try to save the software and write emulators for the hardware. You could present the (non-working) hardware in the museum and have some modern computers with emulators for the old software. You will have to update the emulator park from time to time and maybe you need an emulator to get the 2400er software running, on that one for the 2300er software and so on, until you get your 1983 IBM PC Software running on the mega-quantum-computer-mainframe from 2495.
Now add Virtual reality to this. You will not simply use an emulator, but a VR simulation. In this case it would be best to update all software to the most modern VR simulation system (as automatic as possible).
If you do like this, you have no problems with degrading Hardware, but you still have to keep all VRs up-to-date. And you have to have a VR model of your 1983 IBM PC to run your IBM PC software.
What everyone else says about certain components breaking down is correct as far as I know. That said instead of using a neutral gas you might consider submerging the device to be stored in oil. Pick your oil that does not hurt the plastic. Right now some devices are built to be used with the circuit boards submerged in mineral oil even while the device is being used.
For what you are doing oil would have the advantage over a neutral gas in that an oil bath will help limit any damage caused by components leaking.
The main down check is that you would have a bit of work to clean up an Ipad to use it, but that would be true no mater how you stored it.
I believe all the "No you can't" answers are simply not taking into account the question you are asking--what can be done to preserve them. They all mention easily preventable things like corrosion and batteries. (With the notation that if you won't be able to preserve the batteries, but that shouldn't be an issue in a museum environment)
Here's how you preserve an iPad for the future:
With these precautions taken, I am certain that you would have at least 1 and probably 3 working iPads at the end of 500 years--and once re-powered they would likely work for years.
I don't think the low temp stuff is required or useful... it's oxygen that decays everything, remove that and even a slice of meat will just sit there for years and not decay.
