User Manual

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80 JN-DS-JN5139 v1.5 © Jennic 2008
Figure 54: Recommended Solder Paste Mask for 56QFN Package
• Nine vias are applied to the paddle. These allow excess solder paste and heated air to be vented away from the
device, preventing the device from being lifted during soldering.
Figure 55: Vias on the Paddle of the 56QFN Package
B.3.12 Bespoke Solutions - PCB Layout Suggestions
The list presented below provides some key suggestions when using a wireless microcontroller on a bespoke, multi-
layer PCB. Clearly, the list is not exhaustive and you may have more detailed considerations in using mixed-signal
integrated circuits.
• Shared vias : Often in layout, it is convenient for a number of components to share a return to Analog Ground.
Examples include bypass capacitors and reference setting resistors. We recommend that all components are
given a separate via to ground. This avoids noise feed-through and poor isolation issues that often occur if a
via is shared.
• Oscillator circuit : We recommend that tracks from the oscillator pins are kept to the same length and, ideally,
on the top layer. This avoids asymmetrical loading of the crystal resonator. The placement of the two capacitors
should be symmetrical to the crystal. This also avoids asymmetrical loading of the reference oscillator.