Thermal management of high power electronics with phase change cooling

a study on the prospect of designing high power electronic packages with phase change cooling is presented, with special emphasis on minimising the rising of junction temperatures due to thermal transient effects. The one-dimensional thermal model consists of a finite slab suddenly exposed to a uniform heat flux at the top surface and cooled by convective air at the bottom. The phase change problem is divided into sub-problems and solved progressively. Before the slab starts to melt, both exact and approximate solutions are presented for the distribution of temperature in the slab as functions of time and Blot number Bi. The necessity of partitioning the time domain into two regimes, separated by the time to needed for the thermal front to traverse across the whole slab, is emphasised. After the slab melts, quasi-steady state solutions are obtained both for the melt depth and the evolution of surface temperature as functions of time and Blot number when t(m) > t(0), with t(m) denoting the time needed for melting to commence at the top surface of the slab. The quasi-steady state solutions are compared with those obtained by using the method of finite elements. Approximate but simple analytical solutions are also constructed for the t(m) < t(0) case which, again, are compared with the finite element results. Finally, these solutions are analysed to guide the design of advanced packages with optimised phase change cooling strategies. (C) 2000 Elsevier Science Ltd. All rights reserved.