Electroless Nickel Electroless Palladium Immersion Gold as a pcb finish is for high reliability gold wire bonding, electroless Nickel/Immersion gold can be used for lower end consumer products, however it is not as reliable ENEPIG.

http://www.cube.cz/editor/filestore/Image/technologie/bonding_07_150_x_450.bmp

ADVANTAGES
Palladium Prevents Nickel from Passivating in the Presence of the “Porous”Gold Deposit
Aluminum Wire Bondable
Planar Surface
Good for Fine Pitch Product
DISADVANTAGES
X – Additional Process Step for PCB
Fabricator; Added Cost Results
X – Evidence that Palladium Poisons the
Solder Paste after Reflow
X – Waste Treatment
X – Expensive