Cooling of electronics by liquid-vapour phase change

Thermal management of electronic systems is a crucial issue in many industrial sectors, because of the ever-increasing density of electronic components, due to their miniaturization and the demand for overall power density. The densification of components is linked to the evolution of technologies. For example, Moore's empirical law, and beyond that More-Than-Moore approaches, have enabled the emergence of processors with several trillion transistors per square centimeter, whose size is only a few nanometers. The direct consequence of this law is an increase in switching frequencies and flux densities to be dissipated, which are also increasingly heterogeneous. The same applies to power components and converters. The emergence of new technologies, notably those using gallium nitride, is having the same effect, with power densities now locally exceeding several hundred watts per square centimetre. This situation generates hot spots and leads to high thermo-mechanical stresses. Despite numerous efforts to improve conventional cooling systems, the temperatures reached in the core of components can exceed acceptable limits. Moreover, failure mechanisms are exacerbated by these temperature excursions. Reliability analyses show that the majority of current failures in converters stem from thermal cycling of certain electronic components. For example, in civil and military aviation, thermal stresses now account for 63% of electronic circuit failure sources.

Consequently, the development of more efficient and compact cooling solutions is a major challenge for manufacturers. Solutions based on liquid-vapor phase change are capable of meeting this challenge, as they enable the transfer of large quantities of heat with only a small temperature difference.

After presenting the problems associated with thermal cooling in electronic systems, this article describes two-phase cooling technology solutions, then presents a case study comparing the performance of these technologies with more conventional ones.

A table of symbols and indices is provided at the end of the article.