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MPC7447

RISC Microprocessor Hardware Specifications

Freescale Semiconductor 

System Design Information

Due to the complexity and variety of system-level boundary conditions for today's microelectronic

equipment, the combined effects of the heat transfer mechanisms (radiation, convection, and conduction)

may vary widely. For these reasons, we recommend using conjugate heat transfer models for the board as

well as system-level designs.

For system thermal modeling, the MPC7448 thermal model is shown in Figure 26. Four volumes represent

this device. Two of the volumes, solder ball-air and substrate, are modeled using the package outline size

of the package. The other two, die and bump-underfill, have the same size as the die. The silicon die should

be modeled 8.0 × 7.3 × 0.86 mm3 with the heat source applied as a uniform source at the bottom of the

volume. The bump and underfill layer is modeled as 8.0 × 7.3 × 0.07 mm3collapsed in the z-direction with

a thermal conductivity of 5.0 W/(m • K) in the z-direction. The substrate volume is 25 × 25 × 1.14 mm3

and has 9.9 W/(m • K) isotropic conductivity in the xy-plane and 2.95 W/(m • K) in the direction of the

z-axis. The solder ball and air layer are modeled with the same horizontal dimensions as the substrate and

is 0.8 mm thick. For the LGA package the solder and air layer is 0.1 mm thick, but the material properties

are the same. It can also be modeled as a collapsed volume using orthotropic material properties:

0.034 W/(m • K) in the xy-plane direction and 11.2 W/(m • K) in the direction of the z-axis.

Conductivity

Value

Die (8.0 × 7.3 × 0.86 mm3)

Unit

Silicon

Temperature-

dependent

W/(m • K)

Bump and Underfill (8.0 × 7.3 × 0.07 mm3)

kz

5.0

W/(m • K)

Substrate (25 × 25 × 1.14 mm3)

kx

9.9

W/(m • K)

ky

9.9

kz

2.95

Solder Ball and Air (25 × 25 × 0.8 mm3)

kx

0.034

W/(m • K)

ky

0.034

kz

11.2

Die

z

Bump and Underfill

Substrate

Solder and Air

Side View of Model (Not to Scale)

x

Substrate

Die

y

Top View of Model (Not to Scale)

Figure 26. Recommended Thermal Model of MPC7448

MPC7448 RISC Microprocessor Hardware Specifications, Rev. 4

Freescale Semiconductor

51

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