ENEPIG

ENEPIG stands for Electroless Nickel Electroless Palladium Immersion Gold. It is a surface finish used on printed circuit boards, connectors, and other copper-containing substrates to provide reliable solderability, corrosion resistance, and compatibility with lead-free solder processes. The finish is a three-layer system designed to improve upon some limitations of ENIG.

The typical ENEPIG stack consists of an initial electroless nickel layer, followed by an electroless palladium layer, and finished with an immersion gold layer. The nickel layer acts as a diffusion barrier and base for adhesion, the palladium layer serves as an additional diffusion barrier and improves wetting and solderability, and the ultra-thin immersion gold provides corrosion resistance and a pristine solderable surface. The plating sequence usually involves cleaning and activation, then Ni-P deposition, Pd deposition, and finally immersion gold.

Advantages of ENEPIG include strong solderability for both lead-based and lead-free solders, good long-term corrosion resistance, and improved reliability for fine-pitch and high-density boards. The palladium layer helps reduce nickel diffusion and can enhance rework opportunities on some substrates. ENEPIG is often favored for high-reliability applications such as medical, automotive, aerospace, and complex consumer electronics, where solder joint integrity and compatibility with various components are important.

Disadvantages include higher material and process costs compared with ENIG, and greater process complexity due to the additional palladium deposition step. Availability of materials and process control are important considerations for manufacturers. ENEPIG provides an alternative to ENIG when improved barrier performance and wider solderability are required.