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What Is PCB Immersion Gold ENIG Surface Finish?

The popularity of immersion gold surface finish has grown over the years. Today, it is the trendiest idea amongst others in the industry. Of course, there have been different ways of printing circuit boards in the past. Some were great while others have fallen short in various ways. However, the gold surface finish has managed to stand out in recent times.

Are you wondering what this is all about? There is no need to rack your brains because you have come to the right place. The major aim of this post is to explain more about the gold PCB surface finish. In the end, you will discover why it is currently the best option you can explore.

PCB Immersion Gold ENIG Surface Finish
PCB Immersion Gold ENIG Surface Finish

What Is ENIG Surface Finish?

The first thing to note is that ENIG is an acronym for Electroless Nickel Immersion Gold. It can also be called soft gold, chemical Ni/Au or immersion gold (Au). The formation of ENIG takes place through the deposition of Ni-P alloy. This is usually on a Pd surface that is catalyzed. According to most experts, ENIG is a product of displacement reaction or combination of displacement as well as reduction reaction which take place inside such plating solution.

In most electrical devices we are making use of today, printed circuit boards have proven to be a crucial component. In order to cope with the rigors of various operational environments, they are usually made with different kinds of surface finishes. This enables them to perform optimally while being used. One of such finishes happens to be ENIG.

In simple terms, Electroless Nickel Immersion Gold is a process (metal plating) which is used in the manufacturing of PCB (printed circuit boards). The goal is to ensure oxidation is avoided. It can also enhance the solderability of various copper contacts as well as plated through holes. As said above, there are different types of finishes. However, the most popular right now in the PCB industry seems to be ENIG.

In the process of immersion gold plating, gold (thin layer) is applied through surface atoms displacement. The coating in this process isn’t too thick. Normally, it will be around 3-8micro inches. It can be said that immersion gold is an upgrade of gold plating. That is to say, it is a process that has been introduced to solve the problems which gold plating has been known to have over the years.

What Are The Advantages of ENIG Surface Finish?

The popularity of immersion gold in the PCB industry today can be traced to the advantages and benefits that it can offer. Some of these will be highlighted and briefly explained below.

  • Its Structure Can Be Easily Processed

This is probably one of the most obvious benefits that ENIG has been known for. As compared to Hot Air Solder Leveling (HASL), or Nickel Palladium, it is very easy to process. This is quite obvious when it comes to solderability. PCB immersion gold finishes aren’t complicated or difficult to understand. Organizing their structures is very easy to do.

  • Its Flat Surface

The industry seems to be evolving and Electroless Nickel Immersion Gold is the perfect answer. For instance, there has been the rise of lead-free requirements which demand surfaces that are flat. The same can also be said of surface components that are complicated. Some examples are flip chips and BGAs. The good part is that ENIG is perfect for surfaces that are flat.

  • Great Oxidation Resistance

Surface finishes that are highly resistant to oxidation is one of the conditions or factors that manufacturers of printed board circuits usually lookout for. Unlike Nickel Palladium and HASL, soft gold has been known to tick all of these boxes. It contains electroless nickel plating which is usually covered using immersion gold. With this, the nickel will not be affected by oxidation. In fact, the chances of oxidation occurring is very minimal. Apart from that, such PCB Surface Finish is resistant to corrosion.

  • Optimum Electrical Performance

Whenever printed circuit boards are being manufactured, even the slightest of details matters a lot. How the boards have been designed, wires are being placed and many other factors are considered. Overall, these determine the electrical performance of such circuit boards. With an ENIG finish, various PCB components will work fine as expected.

  • Resistant To High Temperature

Too much heat can cause damage to the integrity of your PCB. For instance, it can make the materials to start expanding. This will affect the transmission lines and other important parts. There are some dangerous implications of this problem like shift and distortion in frequency. Loss of linearity is also another issue that can arise. Above all, heat can lead to circuit board failure.

With a soft gold Surface PCB Finish, all of these problems will be nonexistent. Again, this can help to extend the life of your circuit board.

  • They Are Lead-Free

Studies have shown that too much exposure to lead can bring about health complications like anemia, body weakness, brain, and kidney damage. There are instances when it can even become fatal. With ENIG gold immersion, there is no need bothering about how to deal with lead. This is because it is 100% lead-free.

There are other benefits of soft gold finish that you also need to be aware of apart from what has been explained above. For instance, it is perfect for PTH (Plated Through-Hole). Furthermore, electroplating isn’t required for ENIG surface finishes. Another advantage is that compared to ENEPIG or HASL, welding such finishes is very easy. Finally, ENIG aligns with the requirements of RoHS.

What Are The Disadvantages of ENIG Surface Finish?

Just as this PCB surface finish has lots of advantages, that is how it equally has disadvantages which you should be aware of. This section will be highlighting and explain them.

  • It Is Expensive

This is the first drawback of ENIG PCB surface finish. It has been discovered to be very expensive as compared to other surface finishes like HASL or OSP. The increased cost can be traced to the high prices of gold.

  • Black Pad Occurrence

A black pad is a situation when phosphorus begins to build between gold as well as nickel layers. This will not only bring about fractured surfaces. Also, it can cause problems related to faulty connections.

  • It Is Not Reworkable

Circuit boards that have been designed with Electroless Nickel Immersion Gold are usually not reworkable. In other words, they are quite rigid in many ways. Even when they can be reworked, there are lots of limitations.

  • Possibility of Signal Loss (RF)

This happens when there is a loss of signal power due to a device being inserted into the transmission line. Decibels (dB) is what it is always expressed in. It is a sign that the ENIG deposit contains electroless nickels.

Finally, the process is very complicated to carry out. Designing a circuit board with ENIG, PCB Surface Finish is not straightforward. You need to have some special knowledge and skills before such can be possible.

What Is The Manufacturing Process of ENIG Surface Finish?

Just as mentioned above, the process of manufacturing ENIG, PCB Surface Finish is quite complicated. This section will be revealing how much is done.

The formation of ENIG happens through Ni-P alloy being deposited on a Pd surface that is catalyzed which is generated via displacement reaction. This usually takes place on copper surfaces. Such will then be followed by a gold finish (thin layer).

In the end, the nickel thickness will be approximately 100 – 200µin. The gold will have a thickness of around 10 – 15µin. Below is the process for better understanding.

The first step is covering the pad of the panel with immersion gold. This is done through an auto operator. For a high-quality coating to be achieved, the automated lines will have to maintain the processing time.

The panels are collected in a cassette and will pass through the preparation stages like cleaning, micro watching, and activation.

The cassette will then be plunged into a nickel electroplating bath for approximately 22mins. This will enable the deposition of nickel (5micro layer).

While the coating process is ongoing, the program is going to monitor the parameters of the solution. It will make automatic adjustments wherever necessary with the use of dispensers.

Once the nickel has been deposited, the panels will then be moved to the immersion gold plating where around 0.06 will be deposited on the nickel layer’s surface.

After the rinsing and drying, the panels will go through quality control. When this is done, they will then be transferred to the mechanical processing department.

What is the difference between gold-plated PCB and immersion gold PCB?

Gold plating and Immersion Gold are both methods of PCB surface finish. Click here to learn about their differences.

Final Words

Based on the above, it can be seen that ENIG surface finish is probably one of the best amongst others in the market. Today, manufacturers of circuit boards are using it more than ever before due to the features and advantages it can offer. Despite its shortcomings as mentioned above, there is no doubting the fact that it has managed to meet the present-day demands of electrical devices.

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