Visualization of forced air flows over a populated printed circuit board and their impact on convective heat transfer

Abstract

A detailed characterization of the airflow patterns around Printed Circuit Board (PCB)-mounted electronic components has been undertaken using three different, but complementary flow visualization techniques. Uniform airflows of 2 m/s, 4 m/s and 5.5 m/s were directed over Plastic Quad Flat Pack (PQFP) components mounted on a double Euro-Card PCB. The complexity of PCB topology and resulting flow phenomena, was increased in three stages from just one, centrally placed component, to seven components and finally to the most complex case consisting of a symmetrical in-line array of fifteen components. Traditional smoke- and paint-flow visualization techniques, as well as a novel paint-film evaporation technique, were applied to help identify the sensitivity of the flow phenomena and its impact on convective heat transfer, to both air velocity and PCB topology. Combined, these techniques not only helped characteristic features of these flows such as separation/reattachment points, re-circulation zones and horseshoe vortices to be identified, but also showed in a qualitative way, using the evaporation technique, how these flow phenomena impact on PCB/component surface heat transfer. Linking the flow phenomena with the surface heat transfer in this way also provides, in the early design phase, a means of identifying both an appropriate numerical flow modeling strategy for the flow phenomena present, and the locations of high aerodynamic disturbance on the PCB, where temperature prediction accuracy must be viewed with caution.