Exploring Various Types of PCB Surface Finishes
As a printed circuit board manufacturer, we need to give professional advises about PCB surface finish .Because the PCB surface treatment will have a significant effect on PCB processing quotations. with a quite large difference in PCB surface treatment process charges. So we summaries knowledge of PCB surface finishes. Because PCB surface finish is critical for ensuring the PCB quality, reliability. and performance of electronic devices. It allows designers and manufacturers to make informed decisions. leading to more successful and durable electronic products. let us know the knowledges about PCB Surface Finishes.
What Is the PCB Surface Finishes？
Because the copper in the PCB is easily oxidised in the air. the copper oxide layer has a significant impact on the pad, making it easy to form a false weld. False welds are serious and easily cause the pad and components to be unable to welded. As a result, the PCB will undergo a process in which the surface of the pad coated. with a layer of substances to protect the pad from oxidation.
How PCB Surface Finishes Enhance The Performance and reliability ？
Corrosion Resistance:
One of the primary functions of surface finishes is to protect the exposed copper traces. and pads on the PCB from corrosion and oxidation. Copper, which is commonly used in PCBs, can oxidize over time when exposed to air and moisture. leading to poor electrical conductivity and unreliable connections. Surface finishes create a protective barrier that prevents oxidation, ensuring long-term reliability.
Solderability:
Surface finishes significantly impact the solderability of PCB components. Proper soldering is essential for forming strong. and reliable electrical connections between components and the PCB. Different surface finishes provide varying levels of solderability. ensuring that solder adheres well to the pads and components during assembly. reducing the risk of solder defects like cold solder joints or solder bridges.
Flat and Smooth Surfaces:
Surface finishes can create flat and smooth surfaces on the PCB. which is particularly important for fine-pitch surface mount components. Flat surfaces ensure precise component placement and prevent solder defects. such as solder balling or insufficient solder paste transfer during assembly.
Enhanced Electrical Performance:
Certain advanced surface finishes, such as ENIG and ENEPIG . That have specific electrical properties. that can improve the performance of PCBs in high-frequency and R applications. They help maintain signal integrity by reducing signal loss and impedance variations.
Environmental Protection:
PCBs are often exposed to various environmental conditions. including temperature variations, humidity, and chemicals. Surface finishes provide protection against these environmental factors. ensuring that the PCB remains reliable even in challenging conditions.
High Reliability:
Surface finishes like ENEPIG and ENEPEG are specifically designed for high-reliability applications. such as aerospace, medical devices, and military electronics. These finishes offer superior corrosion resistance and long-term reliability. making them suitable for critical systems.
Compatibility with Lead-Free Assembly:
With the shift towards lead-free soldering processes (e.g., RoHS compliance). certain surface finishes are better suited for lead-free assembly. Immersion silver and immersion tin, for example, are lead-free-compatible finishes. that ensure reliable soldering without the use of lead-based solders.
Ease of Rework and Repair:
Some surface finishes are more conducive to rework and repair processes. Knowing the surface finish used on a PCB can help technicians. choose the appropriate rework methods and materials. to ensure successful repairs without damaging the PCB.
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Types of PCB Surface Finishes
Choosing the right surface finish based on the specific application. and requirements is a critical aspect of PCB design and manufacturing. to ensure the longevity and functionality of electronic devices. we need to know more about types of PCB surface finishes.
| Types of PCB Surface Finish | Pros | Cons | Cost | Thickness (microns) | Preservation |
| Lead-HASL | Uneven plating, mainly used with larger pads, wide line spacing， | Not suitable for HDI boards, dirty process, smell, high temperature operation. | Medium | Pad2-5 Hole≤5 | 1 Year |
| HASL | Compared with lead-free tin, leaded tin has high mechanical strength and good brightness. | Lead is harmful | Medium | Pad2-5 Holed≤5 | 1 Year |
| OSP | Uniform plating, flat surface. Simple process, low price, good welding reliability | However, it is difficult to check the appearance, not suitable for multiple reflow, and anti-scratch. | Low | 0.1-0.5 | 6 Months |
| Immersion Gold | Uniform plating, flat surface. Good weldability, good contact, good corrosion resistance and can assist in heat dissipation. | Improper control of the process will result in gold embrittlement, nickel corrosion, and poor soldering of the original. | High | Ni3-5 Au 0.03-0.08 | 1 Year |
| Immersion Silver | Uniform plating, flat surface, good weldability, can withstand multiple assembly operations, simple and fast process. | However, it requires high environmental storage conditions and is prone to yellowing and discoloration. | Medium | 0.1-0.5 | 6 Months |
| Immersion Tin | Uniform plating, flat surface. Good weldability. | However, tin is difficult to control, poor heat resistance, easy to aging, discoloration | Low | 0.8-1.2 | 6 Months |
| ENEPIG | Uniform plating, flat surface, good weldability, good contact, good corrosion resistance. | Slow reaction speed, high requirements for production control, easy to black plate, gold surface pollution and foreign color problems. | High | Ni2-5 Pd：0.05-0.15 Au 0.05-0.15 | 6 Months |
| ENEPEG | Uneven plating, good contact, good abrasion resistance, weldable. | However, it is a waste of gold, and it is difficult to ensure the adhesion of solder resist on the gold surface. | High | Ni：3-5 Au：0.05 | 1 Year |
Traditional Surface Finishes
1.1. HASL (Hot Air Solder Leveling)
Process of HASL( Hot Air Solder Leveling)
Preparation—Microetching—Silver Deposition—Rinsing and Drying—Post-Treatment
Advantages of HASL (Hot Air Solder Leveling)
- Excellent Solderability: Immersion silver provides excellent solderability. Silver is a highly solderable material, and the thin silver layer. ensures that solder adheres well to the copper pads and components during assembly.
- Flat and Smooth Surface: Immersion silver creates a flat and smooth surface on the PCB. This is important for fine-pitch surface mount components. as it ensures precise component placement and reduces the risk of solder defects.
- Lead-Free Compatibility: Immersion silver is compatible with lead-free soldering processes. making it suitable for RoHS-compliant electronics manufacturing.
- Good Electrical Performance: While not as conductive as copper, silver still offers good electrical conductivity. This makes immersion silver suitable for a wide range of electronic applications. including high-frequency and RF circuits.
- Relatively Environmentally Friendly: Compared to some other surface finishes, immersion silver considered environmentally friendly. as it does not contain hazardous materials like lead or cadmium.
Disadvantages of Immersion Silver:
- Tarnishing: One significant drawback of immersion silver is that it can tarnish over time when exposed to air. Tarnish can lead to a reduction in solderability and potentially affect long-term reliability. Proper handling and storage are essential to mitigate tarnishing.
- Limited Shelf Life: Immersion silver PCBs have a limited shelf life due to the risk of tarnishing. Manufacturers must take precautions to protect the silver layer before and after assembly.
- Cost: Immersion silver is generally more expensive than some other surface finishes. like HASL (Hot Air Solder Leveling) and OSP (Organic Solderability Preservatives). This cost factor may be a consideration for some projects.
1.2. ENIG (Electroless Nickel Immersion Gold)
ENIG Process (Electroless Nickel Immersion Gold):
Preparation—Electroless Nickel—Deposition—Rinsing—Immersion Gold Deposition—Final Rinsing and Drying
Advantages of ENIG (Electroless Nickel Immersion Gold)
- Excellent Solderability: ENIG offers excellent solderability, ensuring that solder adheres well. to the copper pads and components during assembly. The gold layer is highly solderable. and the flat nickel surface promotes uniform soldering.
- Corrosion Resistance: ENIG provides excellent corrosion resistance, protecting the exposed copper from oxidation. This is particularly important for PCBs in high-humidity or harsh environments.
- Flat and Smooth Surface: ENIG creates a flat and smooth surface on the PCB. making it suitable for fine-pitch surface mount components. It helps prevent solder defects like solder balling. or insufficient solder paste transfer during assembly.
- Lead-Free Compatibility: ENIG is compatible with lead-free soldering processes. making it suitable for RoHS-compliant electronics manufacturing.
- Good Electrical Performance: ENIG has good electrical properties. and is suitable for a wide range of electronic applications. including high-frequency and RF circuits.
Disadvantages of ENIG:
- Cost: ENIG is relatively more expensive than some other surface finishes like HASL. and OSP (Organic Solderability Preservatives). This cost factor may be a consideration for budget-sensitive projects.
- Thickness Control: Achieving precise control over the thickness of the gold layer in the ENIG process can be challenging. Variations in gold thickness can affect the cost and performance of the finish.
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Lead-Free Surface Finishes
2.1. Immersion Silver
Immersion Silver Process:
Preparation— Microetching—Silver Deposition—Rinsing—Post-Treatment (Optional)
Advantages of Immersion Silver:
- Excellent Solderability: Immersion silver provides excellent solderability. Silver is a highly solderable material, and the thin silver layer. ensures that solder adheres well to the copper pads and components during assembly.
- Flat and Smooth Surface: Immersion silver creates a flat and smooth surface on the PCB. This is crucial for fine-pitch surface mount components. ensuring precise component placement and reducing the risk of solder defects.
- Lead-Free Compatibility: Immersion silver is compatible with lead-free soldering processes. making it suitable for RoHS-compliant electronics manufacturing.
- Good Electrical Performance: While not as conductive as copper, silver still offers good electrical conductivity. This makes immersion silver suitable for a wide range of electronic applications. including high-frequency and RF circuits.
- Environmentally Friendly: Immersion silver considered environmentally friendly. as it does not contain hazardous materials like lead or cadmium.
Disadvantages of Immersion Silver:
- Tarnishing: One significant drawback of immersion silver. that it can tarnish over time when exposed to air. Tarnish can lead to a reduction in solderability and potentially affect long-term reliability. Proper handling and storage are essential to mitigate tarnishing.
- Limited Shelf Life: Immersion silver PCBs have a limited shelf life due to the risk of tarnishing. Manufacturers must take precautions to protect the silver layer before and after assembly.
- Cost: Immersion silver is generally more expensive than some other surface finishes like HASL and OSP. This cost factor may be a consideration for some projects.
2.2. OSP (Organic Solderability Preservatives)
The Organic Solderability Preservatives (OSP) Process:
Preparation—Chemical Application—Curing—Rinsing
Advantages of OSP (Organic Solderability Preservatives)
- Limited Shelf Life: OSP-treated PCBs have a limited shelf life compared to some other surface finishes. The protective organic layer can degrade over time, affecting solderability. Manufacturers must carefully manage storage and handling to mitigate this issue.
- Durability: OSP may not provide the same level of long-term protection. against environmental factors (e.g., humidity, moisture) as some other surface finishes. Thus, it may not be suitable for PCBs exposed to harsh conditions or extended outdoor use.
- Handling Sensitivity: OSP-treated PCBs can be sensitive to handling. Contaminants from fingerprints or other sources. That can compromise the effectiveness of the organic layer. potentially leading to soldering issues.
- Not Ideal for Multiple Reflows: OSP may not be suitable for PCBs. that require multiple reflow soldering processes. as the organic layer can degrade with each reflow cycle.
Disadvantages of OSP:
- Cost: ENIG is relatively more expensive than some other surface finishes like HASL. and OSP (Organic Solderability Preservatives). This cost factor may be a consideration for budget-sensitive projects.
- Thickness Control: Achieving precise control over the thickness of the gold layer in the ENIG process can be challenging. Variations in gold thickness can affect the cost and performance of the finish.
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Advanced Surface Finishes
3.1. ENEPIG (Electroless Nickel Electroless Palladium Immersion Gold)
ENEPIG Process:
Preparation—Electroless Nickel Deposition—Palladium Activation—Gold Immersion Rinsing—Post-Treatment (Optional)
Advantages of ENEPIG:
- Excellent Solderability: ENEPIG provides excellent solderability. The combination of palladium and gold layers ensures that solder adheres well. to the copper pads and components during assembly.
- Outstanding Corrosion Resistance: ENEPIG offers superior protection against oxidation and corrosion. making it highly suitable for high-reliability and long-life applications.
- Flat and Smooth Surface: ENEPIG creates a flat and smooth surface on the PCB. which is crucial for fine-pitch surface mount components. This promotes precise component placement and reduces the risk of solder defects.
- Compatibility with Lead-Free Soldering: ENEPIG is compatible with lead-free soldering processes. making it suitable for RoHS-compliant electronics manufacturing.
- Excellent Electrical Performance: ENEPIG provides good electrical properties. making it suitable for a wide range of electronic applications. including high-frequency and RF circuits.
Disadvantages of ENEPIG:
- Cost: ENEPIG is more expensive than some other surface finishes like HASL and OSP . The cost factor may be a consideration for budget-sensitive projects.
- Complexity: The ENEPIG process is more complex. and requires careful control compared to some simpler surface finishes. This complexity may increase manufacturing costs.
3.2. ENEPEG (Electroless Nickel Electroless Palladium Electroless Gold)
The ENEPEG Process:
Preparation—Electroless Nickel Deposition—Palladium Activation—Electroless Gold Deposition—Rinsing—Post-Treatment (Optional)
Advantages of ENEPEG:
- Excellent Solderability: ENEPEG provides excellent solderability. The combination of palladium and gold layers. ensures that solder adheres well to the copper pads and components during assembly.
- Outstanding Corrosion Resistance: ENEPEG offers superior protection against oxidation and corrosion. making it highly suitable for high-reliability and long-life applications.
- Flat and Smooth Surface: ENEPEG creates a flat and smooth surface on the PCB. which is crucial for fine-pitch surface mount components. This promotes precise component placement and reduces the risk of solder defects.
- Compatibility with Lead-Free Soldering: ENEPEG is compatible with lead-free soldering processes. making it suitable for RoHS-compliant electronics manufacturing.
- Excellent Electrical Performance: ENEPEG provides good electrical properties. making it suitable for a wide range of electronic applications. including high-frequency and RF circuits.
Disadvantages of ENEPEG:
- Cost: ENEPEG is more expensive than some other surface finishes like HASL and OSP. The cost factor may be a consideration for budget-sensitive projects.
- Complexity: The ENEPEG process is more complex. and requires careful control compared to some simpler surface finishes. This complexity may increase manufacturing costs.
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Emerging Surface Finishes
4.1. Direct Immersion Gold (DIG)
DIG Process:
The DIG process involves the direct immersion of a PCB into a gold plating solution. resulting in the deposition of a thin layer of pure gold onto the exposed copper surfaces. Unlike some other gold-plating methods that involve multiple steps. DIG eliminates the need for intermediate layers like nickel or palladium. The direct gold deposition enhances solderability. and provides a reliable contact surface for components.
Advantages of DIG:
- Solderability: DIG provides excellent solderability. Gold is highly solderable, and the thin gold layer. ensures that solder adheres well to the copper pads and components during assembly.
- Flat and Smooth Surface: DIG creates a flat and smooth surface on the PCB. which is essential for fine-pitch surface mount components. This ensures precise component placement and reduces the risk of solder defects.
- Lead-Free Compatibility: DIG is compatible with lead-free soldering processes. making it suitable for RoHS-compliant electronics manufacturing.
- Simplicity:DIG is a relatively simple and cost-effective process. compared to multi-step gold-plating methods that involve nickel or palladium layers. It reduces the number of process steps and materials, potentially lowering manufacturing costs.
- Good Electrical Performance: While not as conductive as copper, gold provides good electrical properties. making DIG suitable for a wide range of electronic applications.
Disadvantages of DIG:
- Durability: The thin gold layer deposited in the DIG process may not offer the same level of durability and long-term protection. against oxidation as multi-layer processes like ENEPIG or ENEPEG. It may be less suitable for PCBs exposed to harsh environmental conditions.
- Storage and Handling: DIG-treated PCBs can be sensitive to handling. and contaminants from fingerprints or other sources. can compromise the effectiveness of the gold layer. potentially leading to soldering issues. Proper storage and handling precautions are necessary.
- Limited Applications: While suitable for many electronic applications. DIG may not be the best choice for high-reliability or long-life applications. where superior corrosion resistance and durability required.
4.2. Immersion Tin
The Immersion Tin Process:
Preparation—Immersion Tin Deposition—Rinsing—Drying
Advantages of Immersion Tin::
- Solderability: Immersion tin provides excellent solderability. Tin is highly solderable, and the thin tin layer ensures. that solder adheres well to the copper pads and components during assembly.
- Flat and Smooth Surface: Immersion tin creates a flat and smooth surface on the PCB. which is crucial for fine-pitch surface mount components. This promotes precise component placement and reduces the risk of solder defects.
- Lead-Free Compatibility: Immersion tin is compatible with lead-free soldering processes. making it suitable for RoHS-compliant electronics manufacturing.
- Good Electrical Performance: Tin provides good electrical properties. making immersion tin suitable for a wide range of electronic applications.
- Environmentally Friendly: Immersion tin considered environmentally friendly. as it does not contain hazardous materials like lead or other heavy metals.
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Disadvantages of Immersion Tin:
- Whisker Growth: One challenge associated with immersion tin is the potential for tin whisker growth. Tin whiskers are fine, hair-like structures that can grow from the tin surface over time. These whiskers can lead to short circuits and reliability issues in electronic components.
- Limited Shelf Life: Immersion tin-treated PCBs have a limited shelf life due to the risk of tin oxidation. Manufacturers must take precautions to protect the tin layer before and after assembly.
- Sensitive to Handling: Immersion tin-treated PCBs can be sensitive to handling. and contaminants from fingerprints or other sources. That compromise the effectiveness of the tin layer, potentially leading to soldering issues.
- Surface Finish Thickness Control: Achieving precise control over the thickness of the tin layer. in the immersion tin process can be challenging. Variations in tin thickness can affect the cost and performance of the finish.