Electroless Nickel/Immersion Gold, used for surface
mount/LCD's/keypads/wire bonding etc. The finish normally comprises of
approximately 5 microns of electroless Nickel with a very thin topcoat
of Gold in the order of 0.05-0.1 micron thick.
Although it is possible to have a plain electroless gold finish
without the nickel layer, its rarely used as the rapid migration between
the two metals results in a finish that quickly becomes very hard to
solder.
Price wise it is more expensive to use than HASL of silver, which
tends to mean that it is most widely used for key pads or when LCD's are
directly mounted onto the circuit board.
