The routing card has a decoupling capacitor on AREF. This is marked with a silk print on the PCB. For some AVR devices, the AREF pin is a pin which also is part of the high-voltage programming interface. On these routing cards, the AREF capacitor is not mounted, as it would make it impossible to use the high-voltage programming interface. A capacitor can be soldered to achieve better noise performance. A typical value is 10 nF. The footprint for the capacitor is SMD size 0603.