Higher voltage means more current runs through the chip. This in turn makes the chip act stronger, and frequency that isn't stable at lower voltages might be at higher. However, more current means more heat, and heat, can permanently fry your chip. There is also an issue of electromigration, which increases as you bump up the voltage. This can cause damage even if it hasn't overheated. Most notable example, some Intel P4's had a N.S.D.S. thing going on. (Northwood Sudden Death Syndrome) N.S.D.S. only happened if you went over a certain voltage. This voltage is usually said to be 1.6v or just above... Off course, the chip, and it's electrical characteristics are nowhere near in relationship with the Intel Northwood, so when possible electromigration becomes an issue is anyones guess. Of the top of my head, I'd say what ever the manufacturer says is OK for the fastest chip's made in the same process + an extra 10% "should" be safe. This since faster chips really are identical, they have just been rated for higher speeds by testing, also known as "speed binning."
(The phrase "makes the chip act stronger" is really not a proper description of whats going on. It's an attempt to explain what i cant really describe properly, due to lack in language skills. Whats really going on is that the difference between high and low phases are increased. A CPU is ideally switching state uniformly over the whole chip, but in reality its more of waves that rips past the silicone and each wave is one tick of the frequency. If you want a better explanation you'd have to get someone with a better English ability then mine. Sorry.)
Anyway. Overclocking always increase heat output. If your able to drop voltages and overclock you'd see first a drop in temp, and then a raise from that lower baseline. This is why generaly speaking, overclocking always voids your warranty. Realistically nobody can tell if you overvolted or not on the chip, and as such some people undoubtedly will fry there chip, and come back to claim a warranty. Even tho this is possible, there are some strong incentives not to do so. For one, you broke it. You knew overclocking could damage your chip, and overclocking / over volting can do permanent damage that grows worse over time leaving you with a dead chip weeks, or months after you actually did any overclocking. Another reason is simply die to it being illegal, should anyone figure it out, they could actually press charges. Perhaps that ex girlfriend that was getting neglected when you were trying to get another 2MHz out of the chip will testify against you. A worst case scenario lands you in jail for having broken the darn thing, and trying to get a false claim accepted. Very unlikely, but... And finaly. If people who overclock and break there toys end up getting "free" replacements, that means anyone who buys a Panda actually have to pay for the broken one he had, since the money for producing it has to come from somewhere. Just don't do it. Claim warranty, on a item you broke, that is.
B!
