CLIENT ST Microelectronics, Inc., CLIENT Datasheet - Page 53

• Manufacturer Part Number: CLIENT
• Description: STPC Client Datasheet / PC Compatible Embeded Microprocessor
• Manufacturer: ST Microelectronics, Inc.

6. BOARD LAYOUT
6.1 THERMAL DISSIPATION
Thermal dissipation of the STPC depends mainly
on supply voltage. As a result, when the system
does not need to work at 3.3V, it may be to reduce
the voltage to 3.15V for example. This may save
few 100’s of mW.
The second area that can be concidered is un-
used interfaces and functions. Depending on the
application, some input signals can be grounded,
and some blocks not powered or shutdown. Clock
speed dynamic adjustment is also a solution that
can be used along with the integrated power man-
agement unit.
The standard way to route thermal balls to internal
ground layer implements only one via pad for each
ball pad, connected using a 8-mil wire.
Figure 6-1. Ground routing
Note: For better visibility, ground balls are not all routed.
Issue 2.2 - October 13, 2000
With such configuration the Plastic BGA 388 pack-
age dissipates 90% of the heat through the ground
balls, and especially the central thermal balls
which are directly connected to the die, the re-
maining 10% is dissipated through the case. Add-
ing a heat sink reduces this value to 85%.
As a result, some basic rules have to be applied
when routing the STPC in order to avoid thermal
problems.
First of all, the whole ground layer acts as a heat
sink and ground balls must be directly connected
to it as illustrated in
If one ground layer is not enough, a second
ground plane may be added on the solder side.
Figure
Thru hole to ground layer
Pad for ground ball
6-1.
BOARD LAYOUT
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