STPCC4 STMicroelectronics, STPCC4 Datasheet - Page 84

• Manufacturer Part Number: STPCC4
• Description: STPC CONSUMER-II DATASHEET - X86 CORE PC COMPATIBLE INFORMATION APPLIANCE SYSTEM-ON-CHIP
• Manufacturer: 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.
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 use of a ground plane like in Figure 6-29 is
even better.
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Figure 6-27. Recommended 1-wire Power/Ground Pad Layout
Figure 6-28. Recommended 4-wire Ground Pad Layout
Release 1.5 - January 29, 2002
A 1-wire connection is shown inFigure 6-27. 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
the four vias around the ground pad link as in
Figure 6-28. This gives a total of 49 vias and a
global resistance for the 36 thermal balls of 0.5 C/
W.
m) of the copper on the external side of the PCB.
Pad for ground ball (diameter = 25 mil)
Solder Mask (4 mil)
Connection Wire (width = 12.5 mil)
Via (diameter = 24 mil)
Hole to ground layer (diameter = 12 mil)
4 via pads for each ground ball
1 mil = 0.0254 mm