Other PCB surface treatment processes are used less frequently, electroplated nickel gold (ENIG) and electroless nickel electroless palladium immersion gold (ENEPIG) are likely to be used.

ENIG

Electroless nickel immersion gold is quickly becoming the most popular surface finish in the industry. It’s a double layer metallic coating, with nickel acting as both a barrier to the copper and a surface to which components are soldered. A layer of gold protects the nickel during storage.  ENIG is an answer to major industry trends such as lead-free requirements and rise of complex surface components (especially BGAs and flip chips), which require flat surfaces. But ENIG can be expensive, and at times can result in what is commonly known as “black pad syndrome,” a buildup of phosphorous between the gold and nickel layers that can result in fractured surfaces and faulty connections.

-Advantages:

Flat surfaces

Strong

Lead-free

Good for PTH

-Disadvantages:

Black pad syndrome

Expensive

Not good for rework

ENEPIG

Electroless nickel electroless palladium immersion gold is a type of metal plating for PCBs. Developed around a decade ago, this kind of surface finish has gained popularity in recent years for its comparatively low cost to other types of gold plating for PCBs. Over the past several years, prices for palladium have substantially decreased compared to gold. By using palladium plating for PCBs instead of pure gold, PCB plating services can reduce plating costs, making ENEPIG a more popular electronic plating solution.