Electroless nickel / immersion gold (ENIG) is a RoHS compliant finish that provides a very planar surface, a very reliable solder joint and is very resistant to environmental storage conditions, handling etc. ENIG is available on all PCBs configurations except ValueProto®.

The electroless nickel step is an auto-catalytic process that involves deposition of nickel on the palladium-catalyzed copper surface. The reducing agent, containing nickel ions, must be replenished in order to provide proper concentration, temperature and pH levels necessary to create a consistent coating. During the immersion gold step, the gold adheres to the nickel plated areas through molecular exchange, which will protect the nickel from oxidation until the soldering process occurs. The gold thickness needs to meet certain tolerances to ensure that the nickel maintains its solderability.

There are several advantages to using ENIG over other surface finishes for the usability of untreated contact surfaces such as contact points or membrane switches.
ENIG plated PCB