Thermal
Ultimately, the final selection of an appropriate heat sink depends on many factors, such as thermal
performance at a given air velocity, spatial volume, mass, attachment method, assembly, and cost. Several
heat sinks offered by Aavid Thermalloy, Alpha Novatech, IERC, Chip Coolers, Millennium Electronics,
and Wakefield Engineering offer different heat sink-to-ambient thermal resistances, that will allow the
MPC8540 to function in various environments.
16.2.1 Recommended Thermal Model
For system thermal modeling, the MPC8540 thermal model is shown in
Five cuboids are used
to represent this device. To simplify the model, the solder balls and substrate are modeled as a single block
29x29x1.47 mm with the conductivity adjusted accordingly. For modeling, the planar dimensions of the
die are rounded to the nearest mm, so the die is modeled as 10x12 mm at a thickness of 0.76 mm. The
bump/underfill layer is modeled as a collapsed resistance between the die and substrate assuming a
conductivity of 0.6 in-plane and 1.9 W/m•K in the thickness dimension of 0.76 mm. The lid attach
adhesive is also modeled as a collapsed resistance with dimensions of 10x12x0.050 mm and the
conductivity of 1 W/m•K. The nickel plated copper lid is modeled as 12x14x1 mm. Note that the die and
lid are not centered on the substrate; there is a 1.5 mm offset documented in the case outline drawing in
MPC8540 Integrated Processor Hardware Specifications, Rev. 4
Freescale Semiconductor
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