STPCI2(2002) 查看數據表（PDF） - STMicroelectronics
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STPCI2 Datasheet PDF : 111 Pages
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DESIGN GUIDELINES
To avoid solder wicking over to the via pads during
soldering, it is important to have a solder mask of
4 mil around the pad (NSMD pad). This gives a
diameter of 33 mil for a 25 mil ground pad.
To obtain the optimum ground layout, place the
vias directly under the ball pads. In this case no
local board distortion is tolerated.
Figure 6-34. Optimum Layout for Central Ground Ball - top layer
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
6.4.5.3. Heat dissipation
The thickness of the copper on PCB layers is
typically 34 µm for external layers and 17 µm for
internal layers. This means that thermal
dissipation is not good; high board temperatures
are concentrated around the devices and these
fall quickly with increased distance.
Where possible, place a metal layer inside the
PCB; this improves dramatically the spread of
heat and hence the thermal dissipation of the
board.
The possibility of using the whole system box for
thermal dissipation is very useful in cases of high
internal temperatures and low outside
temperatures. Bottom side of the PBGA should be
thermally connected to the metal chassis in order
to propagate the heat flow through the metal.
Thermally connecting also the top side will
improve furthermore the heat dissipation. Figure
6-35 illustrates such an implementation.
Figure 6-35. Use of Metal Plate for Thermal Dissipation
Die
Board
Metal planes
102/111
Issue 1.0 - July 24, 2002
Thermal conductor
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