ABSTRACT:

A transient three-dimensional computational study is performed for passive thermal control of plastic quad flat packages (PQFP) using organic phase change material (PCM) placed in a heat sink under the printed wiring board (PWB). Governing conservation equations for mass, momentum and energy are solved using a finite volume technique.The effects of phase change are handled by a single-domain enthalpy method. It is found that the use of organic PCMs can stabilize the package temperature for transient periods, without substantial weight penalty. The effect of horizontal and vertical package orientations on the thermal response is studied. It is found that the vertical orientation results in convection dominated melting of the PCM, and a slightly improved thermal performance.For the horizontal orientation,melting is conduction dominated.It is found that incorporation of fins in the PCM results in a slight improvement in thermal performance.Results are presented as time-wise variations of maximum package and substrate temperatures,heat transfer histories,velocity vectors,isotherms and melt shapes.