Factors that must be considered
Relative location of high and low conductivity layers in relation to the heat source
A significant portion of the heat dissipated from electronic packages mounted on the surface of PCBs flows through the laminated structure of the board and into the surrounding boundary layer. The heat spreading within the PCB and in turn the effective conductivity can be strongly influenced by the proximity of the high and low conductivity layers relative to the location of the heat source.
Heat source size and location
The manner in which heat moves from the heat source into the layers of the PCB and finally into the surrounding ambient air is influenced by the heat spreading associated with both the size and the relative location of the heat source.
Convective boundary conditions
Although the film resistance is not directly included in the calculation of effective conductivity, it must be considered indirectly through the calculation of the spreading resistance and consequently the effective conductivity.
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