When the I/O count of high performance CPUs goes up as predicted by Moore’s Law and IC semiconductor switching rates increase, it gets hot! The thermal density (watt/cm2) of microprocessors has gone up steadily over the years and it has now reached 100 watt/cm2 or more. For comparison, a nuclear reactor creates a thermal density of 200-300watt/cm2, and the highest thermal density created by man is about 1000 watt/cm2 seen at rocket nozzles. It is predicted that a 45nm node high performance single core processor will require 400watt power dissipation which is impractical given today’s known thermal management techniques.

Thus the trend to multi-core processors that will provide equal performance at only about 100 watt power dissipation requirement. Electronic devices that generate higher thermal density typically end up operating at higher steady state temperatures. This in turn leads to more stress on the IC and solder fatigue failure as these devices go through thermal cycles between room temperature and operating temperature. As a result, stresses in the low k dielectric of the IC and solder bump fatigue are the most likely sources of failures. Today’s high-lead solder bumps on flip chips are fairly robust, and since no good alternatives appears to be on the horizon, are still exempt from the “lead-free” mania. But for how long?