STPCC03 STMicroelectronics, STPCC03 Datasheet - Page 42

• Manufacturer Part Number: STPCC03
• Description: STPC CONSUMER-S DATASHEET- PC COMPATIBLE EMBEDDED MICROPROCESSOR
• Manufacturer: STMicroelectronics

BOARD LAYOUT
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 3.45V, it is interesting to
reduce the voltage to 3.15V, for example, if it is
possible. This may save few 100’s of mW.
The second area to look at is unused interfaces
and functions. Depending on the application,
some input signals can be grounded, and some
blocks not powered or shutdown. Clock speed dy-
namic adjustment is also a solution that can be
used along with the integrated power manage-
ment 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
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Note: For better visibility, ground balls are not all routed.
Issue 1.1 - October 16, 2000
With such configuration the Plastic BGA 388 pack-
age does 90% of the thermal dissipation through
the ground balls, and especially the central ther-
mal balls which are directly connected to the die,
the remaining 10% is dissipated through the case.
Adding a heat sink reduces this value to 85%.
As a result, some basic rules has 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 Figure 6-1.
If one ground layer is not enough, a second
ground plane may be added on solder side.
Thru hole to ground layer
Pad for ground ball