What are the surface treatment methods for PCB boards?

In the PCB (printed circuit board) production process, various surface treatment methods are usually used to improve the performance and reliability of the circuit board. The following are common PCB surface treatment methods:

1. Lead-free HASL (Hot Air Solder Leveling)
Description: Immerse the PCB in a molten tin-lead alloy, and then use hot air to remove excess solder to form a uniform pad.
Advantages: Low cost and good soldering performance.
Disadvantages: Suitable for thicker boards, which may cause uneven board surface and uneven thickness.

2. Lead-free HASL
Description: Similar to traditional HASL, but uses lead-free alloys (such as tin-silver-copper alloy) for surface treatment to comply with environmental regulations.
Advantages: Meets RoHS (Restriction of the Use of Certain Hazardous Substances Directive) requirements.
Disadvantages: The processing temperature is high and may affect some PCB materials.

3. Electroless Nickel/Immersion Gold (ENIG)
Description: First, a layer of nickel is chemically plated, and then the nickel layer is immersed in gold liquid to form a thin gold layer.
Advantages: Provides good solderability and corrosion resistance, suitable for high-frequency and high-density applications.
Disadvantages: High cost and complex process.

4. Electroless Nickel/Electroless Palladium/Immersion Gold (ENEPIG)
Description: A layer of palladium is plated on the electroless nickel layer, and then a layer of gold is plated on the palladium layer.
Advantages: Provides excellent solderability and corrosion resistance, suitable for high-reliability applications.
Disadvantages: High cost and complex process.

5. Immersion Gold
Description: Deposit a layer of gold on the surface of the PCB, which is usually used as a protective layer.
Advantages: The gold layer is uniform and provides good solderability and corrosion resistance.
Disadvantages: The cost of immersion gold alone is high, usually used for high-end applications.

6. Immersion Tin
Description: Deposit a layer of tin on the surface of the PCB to provide solderability.
Advantages: Relatively low cost, suitable for some applications that do not require long-term storage.
Disadvantages: The tin layer is easily oxidized, and long storage time may cause soldering problems.

7. Immersion Copper
Description: Deposit a thin layer of copper on the surface of the PCB to provide solderability and protection.
Advantages: Low cost, suitable for some specific applications.
Disadvantages: The copper layer is easily oxidized and may require additional processing steps.

8. Aluminum Oxide
Description: Use aluminum oxide coating as a surface treatment on aluminum substrates.
Advantages: Good insulation and wear resistance, suitable for high-power applications.
Disadvantages: Mainly used for aluminum substrates, not suitable for traditional FR-4 PCBs.

9. Electroplated Silver
Description: Deposit a layer of silver on the surface of the PCB through an electroplating process.
Advantages: Provides excellent conductivity and solderability.
Disadvantages: The silver layer is easily oxidized and may cause corrosion problems in long-term use.

10. Electroplated Gold
Description: Deposit a thicker layer of gold on the surface of the PCB through an electroplating process.
Advantages: Provides excellent conductivity, solderability and corrosion resistance.
Disadvantages: High cost.

11. Conformal Coating
Description: Apply a protective coating such as epoxy, silicone or polyurethane to the surface of the PCB.
Advantages: Provide additional environmental protection to prevent moisture, dust and chemicals from damaging the circuit board.
Disadvantages: May affect the quality of welding, and the coating needs to be applied after welding.

Each surface treatment method has its specific advantages and applicable scenarios. Choosing the appropriate surface treatment method needs to be determined based on the PCB's use environment, performance requirements and cost budget.