STPCI2 STMicroelectronics, STPCI2 Datasheet - Page 101

• Manufacturer Part Number: STPCI2
• Description: STPC ATLAS DATASHEET - X86 CORE PC COMPATIBLE SYS
• Manufacturer: STMicroelectronics

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
even better.
Figure 6-32. Recommended 1-wire Power/Ground Pad Layout
Figure 6-33. Recommended 4-wire Ground Pad Layout
Figure 6-34
Issue 1.0 - July 24, 2002
is
A 1-wire connection is shown in
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.
the four vias around the ground pad link as in
Figure
global resistance for the 36 thermal balls of 0.5°C/
W.
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
6-33. This gives a total of 49 vias and a
DESIGN GUIDELINES
1 mil = 0.0254 mm
Figure
6-32. The
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