+86-755-27398155
info@pcbonline.com

Home > Blog > ENEPIG vs ENIG: Which Surface Finish is Better?

ENEPIG vs ENIG: Which Surface Finish is Better?

PCBONLINE Team

Wed, Nov 23, 2022

Rating: icon_staricon_staricon_staricon_staricon_star

icon PCB icon 77

Rating: icon_star-xicon_star-xicon_star-xicon_star-xicon_star-x

icon PCB icon 77

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.

ENEPIG PCBs

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 hard gold plating. 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. ENIG has two metallic layers - gold and nickel.

selective ENIG

The ENIG process includes electroplating 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.

ENIG black pads

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.

ENEPIG
ENIG
Withstand multiple reflow soldering
Perfect
Perfect
Selective surface finish
Non-selective
Selective
Solderability
Perfect
Good
Wire bonding reliability
Perfect
Good
Layer thickness uniformity
Perfect
General
Thickness

Au: 0.05μm to 0.15μm

Pd: 0.10μm to 0.20μm

Ni: 3.0μm to 5.0μm

Au: 0.08μm to 0.13μm

Ni: 3.0μm to 6.0μm

Cost
Higher
High

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.

wire bonding

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.

ENIG and ENEPIG PCB manufacturer

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:

    • Independent fabrication of ENEPIG and ENIG PCBs without outsourcing. And ENIG can be selective.
    • High-quality PCB and PCBA manufacturing certified with ISO 9001:2015, IATF 16949, IPC, REACH, RoHS, and UL.
    • We can conduct four-terminal sensing for PCBs used for defense, automotive, and medical during PCB fabrication to ensure no minor deficiencies.
    • After PCB assembly, we conduct functional testing and thermal aging to ensure no soldering defects such as black pads.
    • Free samples for PCB/PCBA/box builds bulky production and free functional testing.
    • One-on-one engineering support throughout your project.

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.


© This article is an original work of the PCBONLINE team. Please indicate the author PCBONLINE if you reprint. If the article is reproduced without permission or indicating the author's source, PCBONLINE reserves the right to investigate the infringement.

instagram_img