HASL vs ENIG: What is the Difference?

HASL and ENIG are both frequent types of surface finish for PCB. Together with immersion tin, immersion silver, OSP, and other methods, they help to increase the longevity of circuit boards and their high performance.

Let’s focus on HASL and ENIG as the widespread methods you most likely will have to deal with in PCB manufacturing. You’ll review the technicalities, advantages, and disadvantages of both processes.

HASL PCB Finish

Hot Air Solder Leveling (HASL) is the most affordable type of surface finish. It is a well-established and solid option featured by nearly every manufacturer. 

HASL PCB Finish

HASL PCB Plating Process

Hot Air Solder Leveling is the process of coating PCB with molten solder. Then, the excess solder is leveled, or just cut off, with hot air knives — blows of hot air across the copper surfaces.

HASL process is involved with tin, which is not a RoHS-compliant material. Yet, a lead-free version of Hot Air Solder Leveling is also available. 

HASL PCB Plating Advantage

Hot Air Solder Leveling has the following strengths, you may exploit to your benefit:

  • Offers excellent solderability.
  • It is widely available at most PCB shops. 
  • Excellent shelf life and the life span of components overall.
  • The low-cost method that is perfectly suitable for consumer electronics. 
  • Has a large processing window.
  • It can easily be reworked and repaired.
  • The process is simple and does not require experienced labor or expensive consumables.
  • It disallows the oxidation of copper.
  • Exposure to high temperatures in the process can serve as another testing method for copper circuitries. 
  • The PCB industry has an extensive experience with this finish, meaning that none of its specificities may come as a surprise. 

HASL offers a good cost-to-value ratio. It’s the reason why manufacturers love to use it in low to moderate-cost electronics manufacturing. 

HASL PCB Plating Disadvantage

Hot Air Solder Leveling also comes with some limitations that you should kindly consider:

  • Produce uneven surfaces.
  • Makes components sensitive to thermal shock.
  • Copper pads are prone to solder bridging.
  • Not suitable for Plated Through Holes (PTH) design approach. 
  • Not an ideal choice for fine pitch components.
  • Contains Lead in the basic version.
  • Lead-Free HASL is not that functional compared to the conventional approach.
  • It’s not appropriate for line binding.
  • Not perfect for cases when tight tolerances are crucial.
  • Has restrictions on extremely thin or thick boards.

If you use Fine-Pitch technology or aim at getting the most reliable components with a low rejection rate, you probably should consider other options. 

When Should You Use HASL PCB Surface Finish?

If you click with hand-soldering well, HASL must be your first choice. It offers the ease of forming solder joints. Adhesion of solder alloy and HASL’s alloy is also good enough since it’s formed on a molecular level. In some cases, HASL is perfect for high-reliability applications.

HASL also will be your primary choice for the production of budget-friendly electronics of various types. 

ENIG PCB Finish

Electroless Nickel Immersion Gold (ENIG) is another fairly common type of surface finish. It requires the usage of expensive consumables, so it’s utilized in the production of high-end PCBs. 

ENIG PCB Finish

ENIG PCB Plating Process

The surface plating applied onto copper pads is done through a chemical process. In it, a nickel layer covers the copper layer, followed by a thin immersion gold layer. It’s done through electrolysis. 

In this composition, gold prevents copper from rusting. The nickel layer can help to nihilate the diffusion between gold and copper. Besides, nickel also adds to the durability and temperature resistance of the components. 

The general process for creating ENIG finish is cleaning, micro-etching, pre-leaching, activation, ENIG plating, and chemical leaching. 

ENIG PCB Plating Advantage

ENIG it’s one of the solid copper finishes, presented with the following benefits:

  • Forms perfectly flat surfaces due to filling all unevenness with planting. 
  • It’s a lead-free finish.
  • It’s ideal for Plating Through Hole applications.
  • Long shelf life and long-life span.
  • Perfect for fine-pitch components and for smaller components.
  • It’s a well-tested process.
  • Aluminum Wire Bonding compatible.

ENIG is ideal for high-cost customer electronics and specialized, industry-level devices and controllers.

ENIG PCB Plating Disadvantage

ENIG also has some weaknesses to consider before opting for it:

  • It is prone to black pad syndrome.
  • It’s nearly one of the most expensive finishes.
  • It’s aggressive to soldering, so a solder mask dam is preferred. 
  • The finish is not re-workable and can hardly be repaired.
  • Prone to damage from ET.
  • Makes PCBs prone to signal loss (RF).
  • A very complex process requiring experienced staff.

If you are looking for cost-effective solutions, ENIG can hardly be your first choice.

When Should You Use ENIG PCB Surface Finish?

ENIG is frequently used in SMT, lead-free soldering, and BGA packages. Data and telecom, consumer, aerospace, military, and medical industries are among the major consumers of ENIG processed electronics.

Besides, you may use ENIG finish to produce flexible PCBs. These are of high need for fabrications of microelectronics. 

Summary

In essence, HASL and ENIG are different finish processes that may help you to achieve distinct manufacturing outcomes. HASL is perfectly suitable for low-cost and mass-production PCBs. At the same time, ENIG is intended for specialized purposes and high-end devices.

There are some aspects in which you have to rely on one or another finish only. Examples are the need to use plating through the hole or prevent black pad syndrome. Guide your choice based on your manufacturing goals. 

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