There have been a lot of scientific papers published on the effects of electromigration, although nearly all of them focus on forced electromigration for chip test purposes. There is almost no literature or documentation on the effects of electromigration neither during normal chip use nor overclocked chips. But when reading about the forced electromigration one can clearly see the similarities with overclocked chips: The higher temperature, the higher possibility for electromigration to occur.
Voltage and heat:
As mentioned earlier, when you have a stubborn CPU, you might want to increase the voltage a bit.
Fig. 5 The relationship between maximum operating frequency and supply voltage.
This figure shows us the relationship between maximum operating frequency and supply voltage. The maximum operating frequency is proportional to (Vth-V) 1,25/V, where we assume Vth is 0,6V. Between 1V and 3V, the operating frequency is approximately proportional to the supply voltage, meaning that if you have a CPU that does 850MHz at 1,5V you will most likely make it run at about 1,0GHz to 1,13GHz when you increase its core voltage to 2,0V.
Increasing the core voltage automatically means higher wattage output of the chip; doubling the voltage means doubling the frequency, but it also increase the total wattage output by about 800%. If a CPU that originally emit 25W it will at double voltage and speed now radiate 200W of heat!
How to get rid of the heat:
Now that we have learned that higher voltage and frequencies result in higher temperatures, it is time to have a look at the countermeasures to it:
CPU cooling becomes an important issue when overclocking. In the last few years, we have seen a trend with big and expensive heatsinks and other, even more sophisticated cooling devices on the commercial marked. When I first entered the world of overclocking, there were no such thing as copper in-laid heatsinks with dual, high CFM fans on it. Everything had to be hand made, and the first time I saw a slot1 Alpha heat sink, I was in awe.
Today, the different companies fight against each other to deliver the best heatsinks ever available; CPU cooling has become a science, and it has become big business.
Not only does it prevent the danger and possibility of electromigration, it also lets you run your CPU much more stably and most likely at a higher speed.
I realize that the average overclockers do it partially for an extra, and free, bang for the bucks and maybe for the sport of it. That means that it is very unlikely that those of you that are doing this for the first time cash out $40-50 for a copper heat sink, but more likely go for a more cost-effective solution.