Abstract:

Traditional thermal analyses of electronic equipment are based on conduction type solvers at the printed wiring board (PWB) level.These require specifications of convection coefficients on the board and component surfaces,which are in most realistic applications unknown.In recent years, with the advancement in computational fluid dynamics (CFD)/ computational heat transfer (CHT) tools, system level simulations have been undertaken to evaluate thermal performance of electronic equipment.Due to the large computational time and storage requirements involved in such simulations, the grid sizes in these are usually not fine enough to obtain adequate details at the board and component levels.In order to accurately predict thermal performance of the complete electronic system, all levels of modeling must be performed in an integrated and efficient manner.

In the present paper, a methodology is described for the integrated thermal analysis of a laminar natural convection air cooled electronic system.This approach is illustrated by modeling an enclosure with electronic components of different sizes mounted on a printed wiring board.First, a global model for the entire enclosure was developed using a CFD/CHT approach on a coarse grid.The solution to the global model was obtained using a finite volume method.Thermal information from the global model, in the form of board and component surface temperatures, local heat transfer coefficients and reference temperatures, and heat fluxes, was extracted.These quantities were interpolated on a finer grid using Lagrangian polynomials and further employed in board and component level thermal analyses as various boundary conditions.Thus,thermal analyses at all levels were connected.The component investigated is a leadless ceramic chip carrier (LCCC).The integrated analysis approach was validated by comparing the results for a LCCC package obtained from integrated thermal analysis with those obtained from detailed system level thermal analysis for the same package.Two optimized boundary condition combinations are suggested for component level thermal analysis.