NC Pin

The NC Pin DFE rule checks for the NC pin connectivity.

Component pins that are not connected to any signal are treated as NC pins. If any routed traces are connected to these NC pins, they may become good antennas. To prevent this problem, the designer should compulsory connect those NC pins to ground.

NC pin existence test
  • Item: Enter the item name.
  • Component Group: Select a target component group that has NC pins.
  • Connected Net: Select a net group to which the component’s NC pin should be connected.
  • List NC Pin: The DFE lists all NC pins.
  • Include One pin net: DFE consider pin which does not have any connection to other component even if which has connection to net as a NC pin.


    Figure 1.
NC pin via exist test
  • Via on PAD near Conner: DFE checks if via exists on the first encountered NC pin pad from each corner side of IC. If the first encountered NC pin pad does not have via on pad, it reports as failed.


    Figure 2.

Result

PollEx DFE reports component pins have no connecting information and displays a ground pattern to which the NC pins may need to be connected.
  • IC (Internally Connected) pin
    • An IC pin is connected internally.
    • The state of the pin might define the internal operation or a signal might be output.
  • NC (No Connection) pin
    • An NC pin is not connected internally.
    • However, if it is connected, for example, to a signal wire, internal noise will increase.
    • It is therefore recommended not to connect the pin to anything, or to connect the pin directly to the power supply or ground.
    • NC pins may, as an exception, be connected internally. Therefore, be aware of this when NC pins are connected to the power supply or ground.
    • The part supplier may provide what to do with each NC pin.

When there are pins with no connection, the designer can get a stability of signal against noise by connecting those pins to ground. Usually commercial (off-the-shelf) components have no NC pins, however FPGA or ASIC may have them.

In some cases, the designer can remove NC pin to reduce manufacturing costs, however it is not a good practice for manufacturing or EMI. To get better effect of component, connect all NC pins to ground.


Figure 3.