PCBgogo

Imagine a PCB as the nervous system of an electronic device, with its copper traces as the vital pathways. However, copper, like many metals, can rust or oxidize when exposed to air. To protect these pathways and ensure a strong connection when you solder components, a protective “coat” called a surface finish is applied. This layer is crucial for both functionality and longevity.

While numerous options exist, two of the most common surface finishes you'll encounter are HASL and ENIG. Let's break down what they are and which one might be right for your project.

What is HASL (Hot Air Solder Leveling)?

HASL, or Hot Air Solder Leveling, is a process where a PCB is dipped in a tin-lead or lead-free solder bath. After the dip, hot air is used to level the solder, giving the finish its name.

Pros:

• Cost-Effective: HASL is a traditional and widely used process, making it the most affordable option.

  
  

• Robust: The solder finish is thick and durable, making it excellent for large, through-hole components and less sensitive to handling.

  
  

• Great Solderability: Since the finish is essentially solder, it provides a very strong, reliable joint.

Cons:

• Uneven Surface: The hot air leveling process can result in a slightly uneven finish, which is not ideal for components with very fine pitches—the tiny, closely spaced legs on modern chips.

  
  

• Not Ideal for Fine-Pitch Components: The unevenness can make it difficult for pick-and-place machines to accurately align and solder fine-pitch parts, which are increasingly common today.

What is ENIG (Electroless Nickel Immersion Gold)?

ENIG is a two-layer metallic coating. First, a thin layer of nickel is deposited on the copper, followed by an even thinner layer of gold. The gold protects the nickel from oxidation and maintains a perfectly flat, clean surface.

Pros:

• Perfectly Flat Surface: ENIG creates a very flat, uniform surface, making it the go-to choice for high-density boards with fine-pitch components (like BGA and QFN packages).

  
  

• Excellent Solderability: The gold layer provides a clean surface for a reliable solder joint, and the nickel acts as a robust barrier.

  
  

• Long Shelf Life: The gold layer prevents oxidation, giving ENIG-finished boards a longer storage life than HASL boards.

Cons:

• Higher Cost: The use of gold and a more complex chemical process make ENIG more expensive than HASL.

  
  

• Potential for "Black Pad": In rare cases, a brittle interface called "Black Pad" can form between the gold and nickel layers. However, modern, well-controlled processes have largely mitigated this risk.

Making the Right Choice

Choosing between HASL and ENIG often comes down to balancing cost, performance, and component type.

• Choose HASL for: Prototypes, hobby projects, or boards with large, through-hole components where cost is the main driver. It's the industry's workhorse—reliable and affordable.

  
  

• Choose ENIG for: High-density, complex boards with fine-pitch components (BGAs, QFNs), and for applications requiring a long shelf life. It’s the premium choice for professional, high-performance electronics.

At PCBgogo, we understand the nuances of every surface finish. We've helped thousands of engineers and designers make the right choice for their projects, whether it’s a simple prototype or a complex, high-volume production run. We are proud to offer both HASL and ENIG, ensuring that no matter your project's needs, you get a board that is not only perfectly manufactured but also tailored to its specific requirements. We believe that choosing the right surface finish is a small decision that makes a huge difference in the long run.