Finish selection is a critical aspect of PCB manufacturing. In this ENIG vs. HASL comparison, we provide a thorough analysis of the two options. The information will help you make the right decision based on your project’s requirements.
What is ENIG Finish?
ENIG stands for Electroless Nickel Immersion Gold. It means a PCB finish that uses a nickel-gold coating to cover and protect the conductive surfaces (pads and traces).
The finish has a golden yellow look owing to the upper gold layer. Its application is a two-stage process. The first step involves coating the surfaces with nickel, followed by a thin plating of gold.
Being electroless, the process uses no electricity. Instead, it requires dipping the PCB in a plating bath. Despite being costly, ENIG offers various advantages that range from functionality to aesthetics.
What is HASL Finish?
HASL is Hot Air Solder Leveling in full. It refers to a type of PCB finish made from a thin layer of solder. The solder is an alloy (typically a tin-lead blend or a tin-copper/silver mix). It’s usually a tin-lead blend or an alloy of tin and copper/silver.
To apply this finish, the board gets immersed in a molten solder bath. It may also be sprayed with the solder. The solder coats the pads and traces.
The coating then undergoes a drying phase using compressed jets of hot air or “hot air knives”. The air knives also help remove excess solder, resulting in a thin layer of protective finish.
HASL is a cost-effective coating for most printed circuit boards. It also produces robust joints, which is one of its main benefits. On the downside, it may not be suitable for some applications, such as high-density boards.
Resource: https://www.semanticscholar.org
ENIG vs. HASL
The two types of finishes are among the most popular, and likely what you will need to choose between for your project. Here is how they compare when used to protect circuit pads and board traces.
Surface Flatness
ENIG produces a flatter surface, given its materials and application method. The better planarity has its advantages, making it a more suitable choice in specific applications.
HASL has a less flat surface characterized by tiny bumps. These can interfere with component assembly, especially when mounting smaller components, such as integrated circuits (ICs).
Solderability
ENIG generally offers excellent solderability. The gold layer protects the underlying nickel from oxidation, ensuring good wetting capabilities during the reflow process. Its flat surface and good wettability make it particularly suitable for smaller SMD devices and fine-pitch components.
However, it is important to note a potential manufacturing defect known as “black pad.” This issue occurs only if the nickel layer suffers from excessive corrosion during the immersion gold process.
While ENIG creates robust and reliable connections under normal conditions, the “black pad” defect, if present, can lead to brittle joints that may fail under stress.
Being a solder alloy (typically Tin/Lead or Lead-Free Tin/Copper), HASL has a pre-tinned surface that improves its wetting and solderability. It produces a surface that excellently supports component mounting, creating sturdy joints.
Fine Pitch Suitability
The flat surface of an electroless gold immersion finish facilitates the mounting of smaller parts with close leads. These are parts that require extreme precision to place and solder. They include BGAs, QFPs, and CSPs.
It’s more challenging to place and solder the fine-pitch components and dense circuits when the finish is HASL. The uneven surfaces that characterize it are more suited for spaced circuits and THT parts.
Reworkability
The reworkability of ENIG is relatively lower due to its delicate layers. This property, along with other qualities, such as cost, makes it less suited for applications requiring frequent repairs.
On the other hand, the HASL surface finish offers higher reworkability characteristics. It withstands re-heating cycles better, making it ideal for prototype boards.
RoHS Considerations
ENIG is a lead-free finish. In other words, it complies with RoHS requirements for hazardous materials in electronics. The compliance makes it a better finish when environmental safety is a significant requirement.
HASL is available in two options: leaded and lead-free. The lead-based version is cheaper and has better qualities. On the other hand, the lead-free variant is a pricier option but safe for the environment.
Shelf Life
The electroless gold immersion finish has a longer shelf life, ranging from 12 to 18 months. In other words, it maintains its quality for longer when stored.
In comparison, the hot air solder leveling finish has a shorter storage life. It maintains its condition for between 6 and 12 months, which means a brief window between application and PCB assembly.
Cost
The materials used to make ENIG (a combination of nickel and gold) make the finish more expensive. It also employs a more complex application process, which adds to the costs.
HASL costs less owing to its more straightforward coating process and the use of cheaper materials. This quality makes it preferable for low-budget projects.
Resource: https://www.researchgate.net
ENIG vs. HASL: Which Is Better?
Each finish type has its own set of unique advantages. Understanding the benefits of each choice is crucial to making an informed decision for your PCB project. Here is a summary of the advantages of each.
ENIG Advantages
- Exceptional planarity that makes it an excellent finish for high-density circuits.
- The gold coating offers outstanding corrosion resistance.
- Prolonged lifespan that allows the storage of bare PCBs for longer before assembling them.
- Ability to withstand heat for multiple soldering or rework cycles.
- The safe materials the finish uses make PCBs compliant with RoHS standards.
- The flat and bright gold surface facilitates visual and optical inspection, making it easier and more accurate.
HASL Advantages
- Outstanding solderability that results in robust and reliable solder joints for critical PCBs.
- Compatibility with different assembly methods, from reflow to hand and wave soldering.
- Cost-effectiveness for high-volume projects and low-budget circuit board types.
- It allows rework, making it a good choice for prototyping and PCB repair needs.
When to Choose ENIG
Choose ENIG if your circuit board is a high-performance type featuring fine-pitched SMD devices, such as BGAs and wire bonding. It will help avoid part placement and soldering problems.
The finish is also a better option if your project requires eco-friendly materials and if it requires a more extended storage period before mounting with components.
Overall, the finish is the best choice for high-reliability, HDI circuit boards with longer life requirements. They include automotive, medical, and telecommunication PCBs.
When to Choose HASL
HASL is an excellent choice if you’re ordering standard PCBs in bulk and when cost is a major factor. These are circuit boards with spaced circuits and through-hole components.
Choose the finish if the boards are likely to undergo repair and rework, such as when creating prototype boards. Lead-free HASL is your best option for RoHS-compliant boards.
In summary, the finish is ideal for general electronics boards with moderate reliability needs and spaced circuits. You only need to ensure you’re using the correct type of solder.
Conclusion
ENIG and HASL are two popular PCB finishes. But while each finish type has its advantages, there are also drawbacks that you must take into account when choosing between the two. One is a costly option that offers superior qualities, while the other is a cost-effective solution for a wide range of applications.
