ENEPIG vs ENIG: Which Surface Finish is Better?

Surface finish is a metal/organic coating on PCB pads. The surface finish protects the copper PCB pads from oxidation and scratches and boosts soldering when in the reflow soldering oven. Among many surface finishes, ENEPIG and ENIG are two types used for rigid PCBs, flexible PCBs, and rigid-flex PCBs with high reliability. ENEPIG and ENIG are better than HASL, OSP, immersion tin, and other surface finishes.

When do you use ENEPIG or ENIG as the PCB surface finish? Which is better?

Part 1: What is ENEPIG

Electroless nickel electroless palladium immersion gold, abbreviated as ENEPIG, is a metallic coating on PCB pads. This type of surface finish has three layers - nickel, palladium, and gold.

In the ENEPIG process, first, a nickel layer is immersed on the copper pads in a nickel electroless bath. Then a palladium layer is plated on nickel through the replacement reaction. Finally, a gold layer is plated on the palladium layer through the replacement reaction in the gold salt bath.

What is the thickness of ENEPIG? Gold is 0.05 microns to 0.15 microns, palladium is 0.1 microns to 0.2 microns, and nickel is 3.0 microns to 5.0 microns.

Wire bonding can be used on PCB pads with the ENEPIG surface finish. For SSOP, TSOP, QFP, TQFP, and PBGA package components, ENEPIG is a suitable surface finish on their PCB pads.

Compared with ENIG, the palladium layer of ENEPIG stops the gold salt solution from "attacking" nickel, and black pads can't happen to ENEPIG. And ENEPIG has perfect solderability and can withstand multiple times of reflow soldering.

However, ENEPIG has process control requirements. Only a few source factory manufacturer has the qualification and capability to apply ENEPIG.

Part 2: What is ENIG

Electroless nickel immersion gold, or ENIG, is also called immersion gold or chemical gold. It has two metallic layers - gold and nickel, which are deposited on the copper pads one after one. It is a selective PCB surface finish, which means on a PCB, ENIG can apply to required pads, while the other surface finish, such as OSP, HASL, or immersion tin, can apply to the rest pads.

The ENIG process includes depositing a nickel layer on the copper pads and then in the gold salt immersing a gold layer through the replacement reaction on nickel.

For ENIG, the thickness range of gold is 0.08 microns to 0.13 microns, and that of nickel is 3.0 microns to 6.0 microns.

ENIG has excellent wear resistance, and it usually applies to PCB pads for plug-ins and presses, such as keyboards, gold fingers, USBs, etc.

For rigid PCBs with a pitch (pad-to-pad distance) within 0.5mm and flexible PCBs, HASL can't apply, and you can use ENIG.

However, black pads may happen to PCBs with the ENIG finish. Black pads refer to the separation of solder joints formed to the nickel layer due to that nickel was reduced in the gold salt solution during the ENIG process. The source factory must have good process control to ENIG.

Part 3: ENEPIG vs ENIG

ENEPIG is better than ENIG.

You can check out a comparison table between ENEPIG and ENIG and details from the below content.

For wire bonding, the gold thickness of ENIG requires to be 0.3 microns and above, but if you choose the ENEPIG finish, the gold thickness is only 0.1 microns. Though palladium is also a precious metal, ENEPIG is a cheaper surface finish for wire bonding. But in most cases, ENEPIG is more expensive because it has both gold and palladium.

ENEPIG is better than ENIG in performances, such as wear resistance, wire bonding reliability, and solderability. This is because palladium is harder than gold, and no nickel is reduced in the immersing gold step.

Besides, ENEPIG has better layer thickness uniformity than ENIG. The layer thickness uniformity of ENIG is affected by current density.

Have Advanced PCB One-Stop Manufactured by PCBONLINE

PCBONLINE is a one-stop source factory PCB manufacturer with two large advanced PCB manufacturing bases and one PCB assembly factory. From PCB prototypes to bulk production, PCBONLINE can independently complete PCB manufacturing, PCB assembly, conformal coating, IC programming, thermal aging, and box build assembly, including the ENEPIG and ENIG processes in PCB manufacturing.

Gold salt used for ENEPIG and ENIG is highly toxic and is a chemical controlled by the state. Many PCB manufacturers don't have the qualification to purchase or store gold salt for production. Besides, they don't have a sewage treatment license to deal with the sewage after the ENEPIG and ENIG processes. so they have to outsource the ENEPIG and ENIG processes from those who can do it. But PCBONLINE's PCB manufacturing base in Jiangsu has its ENIG and ENEPIG line and sewage treatment license.

PCBONLINE has these advantages in ENEPIG and ENIG processes:

Besides ENEPIG and ENIG, PCBONLINE can apply selective OSP, lead-free HASL, immersion tin, immersion silver, carbon ink, and plating silver on PCB pads. If you need cost-effective PCB/PCBA manufacturing from a source factory, please send your inquiry to info@pcbonline.com. When receiving your Gerber and BOM, our engineers will review your documents and give you a transparent quotation. If you choose the wrong surface finish or your design has any other issues, our engineer will tell you and give suggestions before quoting.

Conclusion

ENEPIG is a metallic coating with nickel, palladium, and gold, and ENIG is a metallic coating with nickel and gold. Usually, ENEPIG is more expensive than ENIG, but ENEPIG has better performance. If you need PCBs with ENEPIG or ENIG, contact the source factory PCB manufacturer PCBONLINE to fabricate your PCBs/PCBA at one-stop, and PCBONLINE won't let you down.

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