STPCI2GDYI(2002) 查看數據表（PDF） - STMicroelectronics

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STPCI2GDYI
(Rev.:2002)

X86 Core PC Compatible System-on-Chip for Terminals

STMicroelectronics 

DESIGN GUIDELINES

When considering thermal dissipation, one of the

most important parts of the layout is the

connection between the ground balls and the

ground layer.

A 1-wire connection is shown in Figure 6-32. The

use of a 8-mil wire results in a thermal resistance

of 105°C/W assuming copper is used (418 W/

m.°K). This high value is due to the thickness (34

µm) of the copper on the external side of the PCB.

Figure 6-32. Recommended 1-wire Power/Ground Pad Layout

Pad for ground ball (diameter = 25 mil)

Solder Mask (4 mil)

Connection Wire (width = 12.5 mil)

34.5 mil

Via (diameter = 24 mil)

Hole to ground layer (diameter = 12 mil)

1 mil = 0.0254 mm

Considering only the central matrix of 36 thermal

balls and one via for each ball, the global thermal

resistance is 2.9°C/W. This can be easily

improved using four 12.5 mil wires to connect to

the four vias around the ground pad link as in

Figure 6-33. This gives a total of 49 vias and a

global resistance for the 36 thermal balls of 0.5°C/

W.

Figure 6-33. Recommended 4-wire Ground Pad Layout

4 via pads for each ground ball

The use of a ground plane like in Figure 6-34 is

even better.

Issue 1.0 - July 24, 2002

101/111

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