Thermal Management of Flip Chip Packages

Abstract

Generally speaking, the electrical energy that is supplied to electronic devices is ultimately transformed into and dissipated as heat. This generation of heat is accompanied by a temperature rise at the heat source followed by the transport of heat to regions of lower temperature within and outside the electronics module or package. Within the package transport of heat occurs via a process of thermal conduction in the solid material making up the package. As the heat reaches the external surfaces of the package it is usually transferred to a cooling fluid (e.g., air) via a thermal convection process. In the case of lower power components thermal radiation may also play a role in transferring heat to the surrounding environment. The temperatures within the electronics package will continue to rise until the rate of heat removal from the package is equal to the rate of heat generation. It is worthwhile to note that, even if purposeful active measures were not taken to cool the package, the laws of nature or physics would prevail and limit the temperature rise. However, in most instances, the resulting temperatures would be too high. As shown in Fig. 9.1, based upon the results of a study conducted under a US Air Force Avionics Integrity Program, temperature was identified as a causal factor in 55% of electronic failures [1]. It might be noted that in most commercial applications, electronic packages are not subjected to nearly as severe an environment in terms of vibration, dust or humidity as military avionics, so the percentage of failures caused by temperature are likely to occupy a larger “piece of the pie.” In addition to the effect of temperature on electronic device reliability, it can also play an important role on CMOS circuit performance. Consequently, it is necessary to provide satisfactory cooling for electronic packages by design and not by accident.