Background
There have been numerous studies conducted and software codes developed to perform
thermal analyses at the component, board, and system levels. In general, the user selects a
level of modeling and solves the resulting discretized equations numerically. A model for
convective cooling may be based on the relatively new Computational Fluid
Dynamics/Computational Heat Transfer (CFD/CHT) approach, or traditional semi-empirical
techniques such as thermal network methodology or modified conduction analysis. Generally,
in the traditional approaches for board and component level analysis, the effect of system
boundaries on the micro-climate near the boards and components is ignored. Similarly, in a
system level model, the details of heat dissipation at the board and component levels are
ignored. This strategy is often used to keep the numerical simulation time within acceptable
limits. In order to accurately predict thermal performance of the complete electronic system,
all three levels of modeling (i.e. component, board, and system) must be performed in an
integrated and efficient manner.
Work Accomplished
A general approach was developed for combined system and board level thermal analysis and
was illustrated for two examples. The first was an indirect air cooled avionics chassis and the
second a direct natural convection air cooled system. For each of these, system level
computations were carried out first using CFD/CHT technique. The board level models were
kept relatively simple for these calculations. The results of the system level analysis were
used to determine heat transfer coefficients on the boards. As the second part of the analysis,
convection coefficient information from the system level analysis was interpolated on a finer
grid to construct a board level thermal model.
Importance of including influence of system effects on
PWB level analysis was illustrated.
A new interface for pre and post processing was developed for the system level code.
This allows convenient set up and display of information for system level problems.
