PCB Surface Finishing Explained: Comparing HASL, ENIG, and Hard Gold

　　 In PCB manufacturing, surface finishing plays a crucial role in ensuring solderability, oxidation resistance, and long-term reliability.

It protects the exposed copper surface and directly affects the electrical performance, mechanical strength, and visual quality of the board.

　　 Among all finishing methods, HASL (Hot Air Solder Leveling), ENIG (Electroless Nickel Immersion Gold), and Hard Gold Plating are the most representative — and the most frequently compared — processes in modern PCB production.

HASL (Hot Air Solder Leveling)

Overview: HASL is one of the most widely used PCB surface finishes. It involves coating the copper surface with molten solder and leveling it with hot air.

Advantages:

1、Lowest cost, ideal for mass production
2、Excellent solderability (pure tin surface)

3、Mature and stable process technology

Limitations:

1、Poor surface flatness (solder bumps are visible)
2、Not suitable for fine-pitch components (BGA, QFP)
3、High thermal stress may cause board warpage

ENIG (Electroless Nickel Immersion Gold)

Overview: ENIG is a chemical plating process that deposits a nickel barrier layer followed by a thin layer of gold.This combination provides both excellent flatness and good corrosion resistance.

Advantages:

1、Extremely flat surface — perfect for BGA, QFP, and SMT
2、Excellent solderability and oxidation resistance

3、Longer shelf life
4、Smooth, uniform, gold-colored appearance

Limitations:

1、Higher cost due to gold and nickel materials
2、Risk of “black pad” if the chemical process is not well controlled

Hard Gold Plating

Overview: Hard gold (also known as electroplated gold) is formed by electrochemical plating, creating a gold-cobalt or gold-nickel alloy layer.It offers superior hardness, durability, and conductivity, making it ideal for contact surfaces.

Advantages:

1、Outstanding wear resistance
2、Excellent contact reliability

3、Corrosion-resistant and long-lasting

Limitations:

1、Higher cost due to additional electroplating steps
2、Poor solderability (hard gold contains alloy elements)

3、Requires extra plating traces and process design

HASL vs ENIG: Balancing Cost and Performance

Comparison Highlights:
•Cost:
HASL is the cheapest; 

ENIG is more expensive due to chemical materials.

•Flatness:
HASL has solder bumps;

ENIG is perfectly flat.

•Solderability:
HASL offers the best solderability;

ENIG is good but slightly lower.

•Shelf Life:
HASL ≈ 12 months;

ENIG ≈ 6 months.

•Component Compatibility:
HASL for large-pitch components;

ENIG for fine-pitch (BGA/QFP).

•Appearance:
HASL has a silver/gray finish;

ENIG looks gold and premium.
•Environmental Compliance:

Both lead-free HASL (HASL-LF);

ENIG meet RoHS standards.

ENIG vs Hard Gold: Soldering or Durability?

Comparison Highlights:
•Process Principle:
ENIG: Chemical deposition (no external current);

Hard Gold: Electroplating (requires current and extra design traces).

•Gold Type:
ENIG: Pure gold (soft, easy to solder);

ard Gold: Gold alloy (hard, wear-resistant).

•Surface Flatness:

ENIG: Very flat, ideal for SMT;

Hard Gold: Slight “dog bone” effect at edges.

•Wear Resistance:
ENIG: Poor, easily scratched;

Hard Gold: Excellent, long-lasting.

•Applications:

ENIG: For entire soldering areas;

Hard Gold: For contact and connector areas (gold fingers, pads, etc.).