EXAMINATION OF NATURAL-CONVECTION PLUMES FROM PARTIALLY HEATED PCB PLATES AND ESTIMATION OF THE HEAT-TRANSFER COEFFICIENTS

Accurate values of convection heat transfer coefficients are required for the simulation of the thermal characteristics of printed circuit b oards. This paper presents the results of experiments carried out usin g a Schlieren apparatus to examine the natural convection plumes from a horizontally positioned partially heated printed circuit board plate . It has been demonstrated that for a board with a centrally positione d resistor, the convection coefficients may be approximated to two val ues, one over the heated resistor area and another over the rest of th e plate. These observations were then used in an optimization process to estimate the convection coefficients from such surfaces. Values of 4 W/m2K and 13.5 W/M2K were obtained for the resistor and the adjoinin g unheated sections, respectively. It is concluded that it is not gene rally satisfactory to assume a uniform value for convection coefficien ts during thermal simulation of electronic structures. However, a simp lifying assumption of two values for convection coefficient appears to be acceptable; the lower value applying in the region of convection p lumes and the higher value elsewhere.