ENIG (Akımsız Nikel Daldırma Altın) Prosesi

In the PCB üretim süreci, surface treatment plays a decisive role in the performance, reliability, and service life of the final product. As one of the most popular PCB surface treatment solutions today, electroless nickel immersion gold (ENIG) has become the preferred choice for many high-end electronic products due to its outstanding comprehensive performance.

What is the ENIG process?

ENIG (Electroless Nickel Immersion Gold) is a surface treatment process that deposits a nickel-phosphorus alloy layer on the surface of copper pads through chemical means, followed by a displacement reaction to deposit a thin gold layer. This dual-layer structure maintains excellent soldering performance while providing superior oxidation protection.

Process Principle and Structural Characteristics of ENIG

The ENIG process has two main steps: electroless nickel plating and immersion gold.

First, in electroless nickel plating, a nickel-phosphorus alloy layer (Ni-P) forms on the copper surface. This layer is usually 4-8μm thick, with phosphorus content between 7-11%. This amorphous nickel layer acts as a strong diffusion barrier and a solid base for soldering.

Next, during the immersion gold step, a pure gold layer of 0.05-0.15μm is added on top of the nickel. This gold layer prevents nickel oxidation and ensures good solderability.

Major Advantages of the ENIG Process

1. Exceptional Solderability

The gold layer quickly mixes with solder, revealing fresh nickel. This creates strong Ni-Sn intermetallic compounds.

2. Excellent Oxidation Resistance

The gold layer effectively keeps out oxygen and moisture. This ensures the PCB remains solderable during storage and shipping.

3. Good Surface Flatness

Chemically deposited coatings deliver a smooth surface. This is perfect for high-density assembly and fine-pitch components.

4. Reliable Bonding Performance

The nickel surface works well for gold and aluminum wire bonding. It meets the needs of chip-scale packaging.

5. Comprehensive Coverage Capability

It coats through-holes, blind vias, and buried vias evenly. This meets the needs of high-density interconnections.

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6. Prevention of Copper Migration

The nickel layer stops copper from diffusing into solder joints. This avoids brittle intermetallic compounds.

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Key Quality Control Points for ENIG Process

To maintain the quality of the ENIG process, we need to control several important parameters:

• Nickel Layer Thickness Control: This should stay between 4-8μm. If it’s too thin, “black nickel” may form. If it’s too thick, costs increase without any advantage.
• Phosphorus Content Management: Keep it between 7-11%. This is vital for corrosion resistance and reliable soldering.
• Gold Layer Thickness Control: Aim for 0.05-0.1μm. A thin layer won’t protect well, while a thick layer can weaken solder joints.
• Solution Activity Maintenance: Regular checks and adjustments of the plating solution ensure a stable deposition rate and good coating quality.
• Pretreatment Quality: Clean and properly roughen the copper surface to ensure strong adhesion.

At Topfast, we deliver ENIG PCBs that meet the highest quality standards. We achieve this through automated production and strict process control for our customers.

Comparison with Other PCB Surface Treatment Processes

ENIG has many benefits, but other surface treatment methods are still useful in certain situations. Here are brief descriptions of several common PCB surface treatment technologies:

Hot Air Solder Leveling (HASL)

Hot Air Solder Leveling (HASL) is an old and popular process for PCB surface treatment. It involves dipping the PCB into molten solder and using hot air knives to remove excess solder, creating an even coating.

Process Advantages:

• Cost-effective with stable technology
• Produces a thick solder coating for multiple reflow cycles
• Offers good soldering performance with various alloys
• Effectively repairs minor surface defects

HASL works well for cost-sensitive applications with low surface flatness needs, like consumer electronics, power modules, and industrial control boards. However, as components get smaller, HASL’s flatness issues are becoming more noticeable.

Organic Solderability Preservative (OSP)

OSP creates an organic layer on clean copper surfaces. This layer stops copper from oxidizing at room temperature. During high-temperature soldering, it quickly breaks down, revealing the copper for soldering.

Process Advantages:

• Provides excellent flatness and coplanarity, ideal for ultra-fine pitch components.
• Simple and eco-friendly, with easy wastewater treatment.
• Cost-effective, only 30-50% of ENIG.
• Good coplanarity, suitable for components like BGAs and QFNs.

OSP works well for large-volume mobile devices and high-density consumer electronics. However, its protective layer is fragile, has a short shelf life, and isn’t ideal for multiple soldering.ng cycles also limit its application scope.

Daldırma Gümüş

Immersion silver deposits a thin layer of silver on copper. This happens through a chemical displacement reaction. The silver thickness usually ranges from 0.1 to 0.4 μm.

Process Advantages:

• Excellent surface flatness and coplanarity.
• Good soldering performance, which improves solder joint reliability.
• Ideal for high-frequency applications; silver’s high conductivity enhances signal transmission.
• Environmentally friendly, as it is free from halogens and heavy metals.

The immersion silver process is popular in communication equipment and high-speed digital products. However, designers must consider silver migration and discoloration issues.

Immersion Tin

Immersion tin deposits a layer of tin on copper through a displacement reaction. The thickness ranges from 0.8 to 1.5 μm, ensuring a flat surface and good solderability.

Process Advantages:

• Excellent surface flatness, ideal for fine-pin components.
• Good soldering performance, meets lead-free requirements.
• Moderate cost, between OSP and ENIG.
• Suitable for press-fit connections, with a hard tin layer.

Immersion tin is common in automotive electronics and industrial control. However, tin whisker growth and a short shelf life are challenges that need careful management.

Comprehensive Comparison of ENIG and Other Surface Treatment Processes

Comparison of PCB Surface Finishes

Advantages of Choosing Topfast’s ENIG Services

As a top PCB manufacturer, Topfast excels in the ENIG process:

1. Precision Process Control: We use automated equipment for consistent coating thickness and quality.
2. Strict Quality Inspection: Our quality monitoring system checks everything from raw materials to finished products.
3. Environmentally Compliant Treatment: We have advanced wastewater systems to meet all environmental regulations.
4. Rapid Response Capability: We provide flexible production and quick sample services.
5. Teknik Destek: Our skilled technical team recommends the best surface treatment solutions.

Whether you need ENIG, OSP, immersion silver, or other special treatments, Topfast offers reliable options. Contact our technical team for more information. We’ll help you choose the best surface treatment for your needs.