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ENIG

A flat, coplanar, lead-free surface finish for fine-pitch, BGA and high-reliability boards. PCBWDX plates ENIG to IPC-4552B with XRF-verified thickness and controlled black-pad risk, out of our Shenzhen line.

Nickel 3–6 µm

Gold 0.05–0.1 µm

IPC-4552B

RoHS · REACH · UL

What is ENIG —— Two thin layers over copper, engineered for flatness

ENIG coats exposed copper pads with an auto-catalytic layer of electroless nickel–phosphorus, then caps it with a thin layer of immersion gold. The gold seals the nickel from oxidation until your assembly line; at reflow it dissolves into the solder, while the nickel becomes the joint.

It is chosen over hot-air leveling and organic finishes because it delivers an ultra-flat, coplanar surface — essential for BGA, CSP and fine-pitch devices where solder joints must sit on a level pad.

ENIG is fully lead-free and RoHS compliant, carries roughly a 12-month shelf life in dry pack, and survives multiple reflow cycles.

It is not the right choice for sliding edge fingers (use electrolytic hard gold) or heavy aluminum wire bonding (use ENEPIG).

How ENIG is plated, step by step

The control window lives in steps 4–6: bath chemistry, loading rate and phosphorus level decide whether the nickel stays corrosion-free.

Clean & deburr

Remove oils, oxides and handling residue from the copper surface.

Copper microetch

Create a micro-rough, activated copper surface for adhesion.

Rinse & activate

Prepare the surface for electroless deposition.

Electroless Ni–P

Self-catalyzed bath builds the 3–6 µm nickel barrier.

Intermediate rinse

Prevent bath carry-over into the gold line.

Immersion gold

Displacement reaction deposits the thin 0.05–0.1 µm Au cap.

Rinse, dry, inspect

Final rinse, dry, 100% visual and electrical test.

Governing standard	IPC-4552B	Electroless nickel (Ni-P)	Ni-3-6 m (120-240pin)
Immersion gold	0.05-0.1 m (2-4 in)	Compliance	RoHS . REACH . UL
Build class	IPC Class 2/Class 3	Thickness check	XRF per lot + cross-section
Solderability	Wetting balance per IPC	Shelf life	~12 months (dry pack)

Gold above ~0.1 µm adds cost and raises gold-embrittlement risk; nickel below 3 µm fails to protect the copper. We hold the middle band on purpose.

When to specify ENIG

Ultra-flat & coplanar

Level pads for BGA, CSP, QFN and fine-pitch devices down to 0.5 mm pitch.

Long shelf life

~12 months in dry pack and tolerance for multiple reflow cycles.

Contact-ready pads

Stable surfaces for switches, buttons, test points and contact pads.

Lead-free & compliant

RoHS and REACH compliant, built for modern assembly requirements.

ENIG vs. other surface finishes

Not every finish wins on every board. Pick by coplanarity, shelf life, contact needs and budget.

Finish	Flatness/fine pitch	Shelflife	CostvsENIG	Bestfor
ENIG	Excellent	~12mo	Baseline	BGA, fine-pitch, contact pads, high reliability
LF-HASL	Poor(uneven)	6-12mo	-70-80% lower	Cost-sensitive, through-hole, coarse pitch
OSP	Good	≤6 mo	Lower	Low-cost SMT, single reflow
ENEPIG	Excellent	-12 mo	Higher	Wire bonding, toughest black-pad resistance
Immersion silver	Good	-6mo	Mid	High-frequency / RF, careful handling
Hard gold	Excellent	Long	Highest	Edge fingers, connectors, wear contacts

The risk buyers ask about

Black pad is the defect most associated with ENIG. It is not normal and it is not unavoidable — it is a process-control problem.

What it is

During gold displacement, the bath over-corrodes the nickel, leaving a phosphorus-rich, brittle surface.

Joints look fine at first but fracture brittlely under stress — intermittent opens, BGA cracking.

Often passes incoming ICT, only to fail later in the field.

Typical causes: over-active gold bath, high phosphorus (>~10%), loose bath loading control.

How PCBWDX controls it

Tight electroless nickel bath chemistry and phosphorus band control.

Displacement gold bath managed for loading rate and bath age.

Nickel-corrosion acceptance per IPC-4552B on sampled cross-sections.

XRF thickness verification on every production lot.

Wetting / solderability and peel-strength sampling.

Design & ordering notes

Use NSMD pads where possible and keep an adequate annular ring.

Mark contact / switch pads separately from pure solder pads — gold can be tuned.

Specify hard gold for edge fingers, ENEPIG for wire-bond pads.

Budget for a ~15–25% premium over LF-HASL on comparable boards.

Store boards in dry pack and avoid hand contact on finished pads.

Send Gerber / ODB++, IPC class, mask spec and target Ni / Au thickness.

Where our ENIG boards land

Medical devices

Aerospace & defense

Telecom & networking

Industrial control

Automotive

BGA / CSP / HDI

Questions engineers ask before ordering

What does ENIG stand for?

Electroless Nickel Immersion Gold. A two-layer, lead-free surface finish: electroless Ni–P plated over copper, capped with a thin immersion gold layer.

What is the difference between ENIG and ENEPIG?

ENEPIG adds an electroless palladium layer between nickel and gold. It resists black pad better and supports more reliable wire bonding, at a higher cost.

Is ENIG RoHS compliant?

Yes. ENIG is lead-free and fully RoHS and REACH compliant.

What nickel and gold thickness should I specify?

Per IPC-4552B: nickel 3–6 µm, gold 0.05–0.1 µm (2–4 µin). Contact pads may use a slightly thicker gold cap; pure solder pads should stay on the thin side.

Is ENIG good for wire bonding?

Limited aluminum wedge bonding is possible, but for reliable wire bonding you should specify ENEPIG.

Why is ENIG more expensive than HASL?

The multi-step chemistry and gold content make ENIG roughly 15–25% pricier than lead-free HASL on comparable boards.

What is black pad and how do you prevent it?

Black pad is over-corrosion of the nickel during gold displacement, causing brittle joints. It is prevented by bath chemistry and phosphorus control, plus IPC-4552B corrosion verification.

Can ENIG be used for edge connectors/gold fingers?

No. Specify electrolytic hard gold for sliding edge fingers; the ENIG gold layer is too thin for wear.

What is the shelf life of ENIG boards?

About 12 months in dry / vacuum packaging — longer than OSP.

Is ENIG good for high-frequency /RF?

Immersion silver is often preferred above ~5 GHz because surface roughness affects insertion loss; ENIG works but should be evaluated for very high-speed / RF builds.

OSPvs ENIG -which should I choose?

OSP is cheaper and fine for single-reflow consumer boards; ENIG wins on flatness, shelf life, handling, multi-reflow and contact pads.

Can ENIG boards be reworked /re-assembled?

Yes, ENIG tolerates multiple reflow cycles; rework follows standard SMT practice.

How do you verify thickness and quality?

XRF on every lot, plus cross-section, wetting balance and visual / electrical inspection, built to IPC-4552B.