When Capacitors Spring Leaks
Electrolyte has leaked from the capacitors next to an AGP connector.
Interior ESR is basically defined by the electrolyte's conductibility. Hence, electrolytes used in low ESR capacitors have to be especially conductive. To increase the conductibility of the electrolyte, you add additives. One of these additives is water. And because of this water allotment, the number of free ions and therefore the electronic conductibility increases.
However, unclean water can attack the aluminum body of the capacitor, which causes corrosion. The corrosion process creates gases inside the capacitor, increasing the interior pressure - you can see a failing capacitor turn lumpy. The top of the capacitor has a predetermined breaking point, so the gas can escape in case pressure gets too high. Yet, from time to time top will not rip open and the capacitor will explode with a bang. The same thing happens in case of extreme overvoltage. The electrolyte still present can pollute the motherboard and cause short circuits, which might even set a computer on fire. Motherboard breakdowns caused a number of problems between 1999 and 2005 for some manufacturers. Capacitors with improper or low-grade electrolytes were used, causing numerous failures and a drastic decrease in motherboard life.
But not only unclean electrolytes can damage capacitors. Like any other liquid, the electrolyte can simply change its physical condition and evaporate. This happens not only when a system is in operation, but can also occur while the system is shut down or the motherboard is stored somewhere. We all know that components such as RAM and CPUs benefit from proper cooling. Cooling also increases the life expectancy of capacitors, since the probability of evaporation correlates with ambient temperature. An unwritten law says that a 10°C drop in temperature doubles the life expectancy of a capacitor.