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2.2.4
PCB Keep-out Zones
Another key PCB design element is the keep-out zone. The keep-out zone is the distance on each
side of the CSP component to the nearest adjacent component on the board. This keep-out zone
varies depending on the application and is generally much tighter in handheld applications that
require many components in a very small PCB area. While system designers often design keep-out
zones anywhere from 0.100 to 0.050 inches (2.54 mm to 1.27 mm) for embedded applications,
many handheld applications are trending toward 0.025 inches (.635 mm) and smaller. The key
factor to consider is how the component needs to be reworked if the component is replaced. Some
Original Equipment Manufacturers (OEMs) require rework using a hot air nozzle that isolates the
rework area to the specific component that is being reworked. Pay special considerations for
allowing adequate area for the hot air nozzle to surround the CSP being reworked. Currently, there
is no rework procedure for the FS-CSP product.
Another factor that impacts the PCB keepout area requirements is the use of a socket. While
sockets are only used during product development, the sockets require larger keep-out areas to
accommodate mechanical mounting holes. The sockets often require backing plates that prevent
the use of decoupling components under the IC package where the components are most effective.
2.2.5
Recommended Mobile Handset Dimensions
For VF-BGA and FS-CSP packages with bodies >12xY mm and <=14x14 mm, the distance from
board edge to center of package is 14.5 mm (package edge is always 2.5mm from support point).
See
Figure 2-9
Figure 2-9. Recommended Mobile Handset Dimensions Diagram
®
Intel
PXA27x Processor Family Design Guide
for illustration of the PCB recommended dimensions.
PCB Design Guidelines
I:2-11
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