User's Manual

AVR2043
13
8345A-AVR-11/10
bottom ground connection can help to keep this connection separate and prevent the
layout tool from flooding across this trace.
When designing applications for very harsh environments, for example where the
radio transceiver is close to mains power lines and burst and surge requirements
already dictate special provisions in the design, the above reference crystal design
might not work well. In this case, the reference crystal ground is to be directly
connected to top and bottom layers.
5.4 PCB – analog GND routing
With the Atmel AT86RF231, consider pins 3, 6, 27, 30, 31, and 32 as analog ground
pins.
Analog ground pins are to be routed to the paddle underneath the IC. The trace width
has to be similar to the pad width when connecting the pads, and increase, if
possible, some distance from the pad.
Figure 5-5. Board layout – transceiver GND.
Each ground pin should be connected to the bottom plane with at least one via. Move
the vias as close to the IC as possible. It is always desired to integrate the single-pin
ground connections into polygon structures after a short distance. Top, bottom, and,
on multilayer boards, the inner ground planes, should be tied together with a grid of
vias. When ground loops are smaller than one tenth of the wavelength, it is safe to
consider this as a solid piece of metal.
The soldering technology used allows the placement of small vias (0.15mm drill)
within the ground paddle underneath the chip. During reflow soldering, the vias get
filled with solder, having a positive effect on the connection cross section. The small
drill size keeps solder losses within an acceptable limit. Vias should be open on the
bottom side to allow enclosed air to expand during the soldering process.