The major cause of system breakdown used to be overheating of critical components. At the hottest points in some of these systems, semiconductor junctions can reach 150 °C or more, getting very close to the limits of their operation. These high temperatures will modify and eventually destroy the circuit operation unless excess heat is removed from the chip. But failure analysis shows that in today’s system designs, this is not the only problem. Typical component breakdown can also be caused by repeated thermal transients. Heating and cooling induces shear stresses at the material interfaces in the package structure (die attach, solder joint), which result in delamination, tear off, etc. The lack of heat removal through the resulting diminished contact area can cause thermal runaway.