BOARD LAYOUT
Figure 6-6. Bottom side layout and decoupling
Ground plane for thermal dissipation
Via to ground layer
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 through the met-
al. Figure 6-7 illustrates such an implementation.
Figure 6-7. Use of metal plate for thermal dissipation
Die
Board
Metal planes
Thermal conductor
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Issue 1.7 - February 8, 2000