Higher temperatures exacerbate a problem known as Electromigration. In the simplest of terms, electromigration is a result of the movement of electrons over a rough surface. IC’s or integrated circuits have small imperfections in the metal connections into the semiconductors. These imperfections are similar to a pothole or a crack in a roadway. The harder the car rides over the pothole, the more likely the car is to break a chunk of the road off and enlarge the pothole. The worse this hole becomes, the more cars hit it harder even if their speed is lowered.
The worsening of the imperfection accelerates the destruction of the metal connector. In a perfect conductor the road surface is perfect, with no bumps or imperfections. In cheap electronics the road surface is already marked with many holes. This is also why high quality electronics have a better chance of surviving massive power surges. The higher quality the path the more likely it is to survive the equivalent of a tank battalion driving over it. It might be damaged by the process, but it is much more likely to survive the encounter and still function for a while longer.
What heat does to this problem, is it makes the road brittle by stretching it out a bit. The pieces of road are much more likely to break off when hit because they aren’t being hung onto as well as they used to be. In silicon the thermal barrier is a specific temperature. Up until a certain point the acceleration is very low. Once that point is reached the problem expands rapidly.
For bulk silicon this thermal limit is about 80 Degrees Celsius, in Strained Silicon or SOI this is closer to 90 or 95 Degrees. Proper cooling can help keep your electronics running better, for longer. This is because the migration won’t occur all at one time and can be extremely difficult to diagnose as it progresses. The main sign is an intermittent error or failure that can be temporarily remedied by lowering the temperature or the voltage to the part.
In my case I had an old Core 2 Duo e6300. This was an old 1.86ghz dual core processor, when I needed more power I ramped it up to almost 3.3ghz which is a huge overclock even with the additional cooling I was using. It lasted for about a year at this level before it killed the motherboard I was using, which was an Asus p5k-se. The motherboard failure put more stress on the chip, which would now only clock up to about 2.7 ghz. Any higher and the system would blue screen inside Windows. Eventually it wound down to about 2.2 ghz max clock and I replaced and retired it. This chip was headed to its eventual end, cpu’s are designed with about a 10 year operational limit in mind. By increasing the load on the chip and increasing the heat it was generating I accelerated its eventual death. It still lasted a good 4 years, but this was a first hand example for me the destructive side effects of electromigration.