Gerald W. Recktenwald and Peter Butler.
Presented at the 1991 ASME Winter Annual Meeting, 1-6 December 1991, Atlanta, GA.
ASME Paper No. 91-WA-EEP-36.
We describe a new approach to using computational fluid dynamics (CFD) in the modeling of convectively cooled printed circuit boards (PCB's). The model is based on a two-dimensional, depth-averaged approximation to the flow field above the devices on the PCB. The depth-averaged flow equations are obtained by integrating the three-dimensional continuity, momentum and energy equations over the direction normal to the plane of the PCB. This approach, which renders the entire PCB in a plan view, is in contrast to other two-dimensional models that analyze the flow in an elevation view. The depth-averaged model provides a more detailed, and a less problem dependent, analysis than lumped parameter models because it computes the flow field and the temperature field of the coolant over the devices. A depth-averaged model also has significantly smaller computing requirements (both run-time and memory) than a fully three-dimensional CFD model of the flow over the PCB. Though the depth-averaged approach is necessarily less detailed than a fully three-dimensional model, we believe that the depth-averaged model is better suited to interactive design analysis. The goal of this research is to develop a tool that will allow packaging engineers to interactively analyze the thermal characteristics of different board layouts at the same time that the electrical and electronics engineers are selecting the devices to be put on the board. Eventually, such an approach could be incorporated into CAD packages.
In this paper we describe the theory of the depth-averaged model and we identify the strengths and weakness of this approach. Several theoretical and practical issues need to be resolved before this strategy can be applied with confidence to the analysis of electronic cooling problems. As a progress report on this research we present preliminary results obtained by simulating related experimental studies in the laminar flow regime.