PCB Surface Finishes: HASL, ENIG And Hard Gold

ENIG vs HASL vs Hard Gold: Key Differences in PCB Surface Finishes

HASL

(Hot Air Solder Leveling)

· Most common

· low cost

· Limited flatness

· Thickness: 1-40 μm

ENIG

(Electroless Nickel Immersion Gold)

· Flat surface

· Good solderability

· Nickel (Ni): 3-5 μm

· Gold (Au): 0.25-1.27 μm

Hard Gold

(Electroplated Hard Gold)

· Excellent contact reliability

· High wear resistance

· Gold (Au): 0.025-0.127 μm

· Nickel (Ni): 3-5 μm

PCB Surface Finishes: HASL, ENIG And Hard Gold

Comparison Between HASL and ENIG

Characteristic	HASL	ENIG	Notes
Cost	Low	High	ENIG requires expensive nickel and gold chemicals; HASL is the most cost-effective option.
Surface Flatness	Poor	Excellent	HASL pads have solder domes (not flat); ENIG produces very flat and uniform surfaces.
Solderability	Excellent	Good	HASL provides a pure tin surface (excellent for soldering); ENIG’s nickel layer is solderable but inferior to pure tin.
Shelf Life / Oxidation Resistance	12 Months	6 Months	HASL can still solder well after long storage; ENIG surfaces are stable but sometimes specified with shorter shelf life.
Suitable Components	Large-pitch components	Fine-pitch components (BGA, QFP, etc.)	Uneven HASL may cause bridging in fine-pitch parts; ENIG flatness is essential for BGA and fine-pitch SMT.
Environmental Compliance	Leaded HASL is non-RoHS; lead-free HASL is RoHS-compliant	RoHS-compliant	ENIG contains no lead and fully meets RoHS. Modern HASL is usually lead-free.
Additional Applications	Soldering only	Also for contact surfaces (e.g., gold fingers, keypads)	ENIG’s gold layer is durable and conductive, suitable as a contact surface.
Process Risks	Thermal stress may cause board warpage	“Black pad” risk	HASL uses high temperature and may warp boards; ENIG can suffer nickel corrosion if process control fails.
Appearance	Bright silver (leaded) or matte silver (lead-free)	Gold color, aesthetically pleasing	HASL is rough-looking; ENIG is smooth and visually attractive.

Comparison Between ENIG and Hard Gold

Characteristic	ENIG	Hard Gold Board	Notes
Process Principle	Chemical displacement plating	Electroplating (requires external current)	ENIG is purely chemical; hard gold requires current and plating connections.
Gold Type	Pure gold (soft gold)	Gold-cobalt or gold-nickel alloy (hard gold)	Soft gold is ductile; hard gold is wear-resistant.
Gold Thickness	Thin, typically 0.025–0.127 μm	Thick, typically 0.25–1.27 μm or more	ENIG uses very thin gold for solderability; hard gold has a thick layer for durability.
Nickel Thickness	3–5 μm	3–5 μm (as base layer)	Both require nickel as a diffusion barrier.
Surface Flatness	Excellent, very flat, suitable for SMT fine-pitch	Moderate, may show edge effect	ENIG ensures flatness; electroplating can cause non-uniform edges.
Wear Resistance	Poor, soft gold is easily scratched	Excellent, very durable	Hard gold is highly resistant to insertion/removal cycles.
Solderability	Excellent, pure gold has slow oxidation	Poor, alloy gold oxidizes and is not recommended for soldering	ENIG for soldering, hard gold for wear resistance.
Cost	Lower, simpler process, economical for mass production	Higher, requires electroplating steps, more gold consumption	Hard gold plating is costly due to extra process and thicker gold.
Applications	Mainstream: SMT, BGA, fine-pitch packages in consumer electronics, telecom, etc.	Special use: edge connectors, gold fingers, test pads, frequent contact areas	ENIG for soldering; hard gold for wear areas.
Design Considerations	No special layout requirement, can cover full PCB	Requires plating traces (thieving lines), increases layout complexity	Hard gold requires specific PCB design features for plating.
Common Issues	Black pad: nickel layer corrosion leads to brittle solder joints	Uneven thickness: thicker at edges, thinner in the middle	Process control is critical for both.