STPCC03 STMicroelectronics, STPCC03 Datasheet - Page 44

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

BOARD LAYOUT
The PBGA Package dissipates also through pe-
ripheral ground balls. When a heat sink is placed
on the device, heat is more uniformely spread
throughout the moulding increasing heat dissipa-
tion through the peripheral ground balls.
The more via pads are connected to each ground
ball, the more heat is dissipated . The only limita-
tion is the risk of lossing routing channels.
Figure 6-5 shows a routing with a good trade off
between thermal dissipation and number of rout-
ing channels.
A local ground plane on opposite side of the board
as shown in Figure 6-6 improves thermal dissipa-
tion. It is used to connect decoupling capacitances
but can also be used for connection to a heat sink
or to the system’s metal box for better dissipation.
This possibility of using the whole system’s box for
thermal dissipation is very usefull in case of high
temperature inside the system and low tempera-
ture outside. In that case, both sides of the PBGA
should be thermally connected to the metal chas-
sis in order to propagate the heat flow through the
metal. Figure 6-7 illustrates such implementation.
44/59
Figure 6-4. Optimum layout for central ground ball
Issue 1.1 - October 16, 2000
6.2 High speed signals
Some Interfaces of the STPC run at high speed
and have to be carefully routed or even shielded.
Here is the list of these interfaces, in decreasing
speed order:
1) Memory Interface.
2) Graphics and video interfaces
3) PCI bus
4) 14MHz oscillator stage
All the clocks haves to be routed first and shielded
for speeds of 27MHz or more. The high speed sig-
nals follow the same contrainsts, like the memory
control signals and the PCI control signals.
The next interfaces to be routed are Memory, Vid-
eo/graphics, and PCI.
All the analog noise sensitive signals have to be
routed in a separate area and hence can be rout-
ed indepedently.
Clearance = 6mil
External diameter = 37 mil
Via to Ground layer
hole diameter = 14 mil
Solder mask
diameter = 33 mil
Pad for ground ball
diameter = 25 mil
connections = 10 mil