PCB surface finishes are available in different types. Surface finish is a crucial aspect of PCB manufacturing. It prevents exposed copper pads from oxidizing. Therefore, surface finishes are crucial for enabling a connection between a board and its component. These days, surface finishes must comply with some standards in the PCB industry. This means that these surface finishes must be lead-free.
The elimination of lead in PCB surface finish is a great achievement in the PCB industry. Most manufacturers focus on getting the right surface finish. A good surface finish must contain no lead. Therefore, the ENEPIG and ENIG are examples of such surface finishes.
The objective of a surface finish is to create a strong connection while meeting environmental demands. ENEPIG and ENIG fall into this category. Therefore, we will have an in-depth look into these two surface finish types.
What is ENEPIG?
ENEPIG stands for Electroless Nickel Electroless Palladium Immersion Gold. It is a type of PCB surface finish that contains no lead. ENEPIG has three metallic layers. It has a layer of electroless nickel. The second layer is electroless palladium and the final is immersion gold. This is why it is popularly known as Electroless Nickel Electroless Palladium Immersion Gold. However, you can call it ENEPIG.
It is a type of metal plating developed for circuit boards. Over the years, ENEPIG has become popular for its cost-effective benefit. Also, it is a preferred option to other gold plating methods. The cost of palladium is less than that of gold. Therefore, the use of palladium during the PCB plating is an ideal option. Also, it is better than pure gold.
ENEPIG is a better and more popular surface finish. Due to its benefits, it is popularly known as the “universal surface finish.” This is because manufacturers can deposit it on any PCB assembly. Also, you can use ENEPIG finishes to support soldering and gold wire bonding. Asides from that, ENEPIG has a longer shelf life than most PCB surface finishes.
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The Three Metallic Layers of ENEPIG
ENEPIG comprises three layers of metal. These layers are deposited on a PCB surface. Also, these layers include nickel, palladium, and gold. The copper layer is the layer that demands protection. Therefore, the manufacturer selectively activates the copper layer. Therefore, this determines the pattern of deposition.
Electroless nickel
This is the first metallic layer in ENEPIG. Electroless nickel serves as a barrier. Therefore, it prevents copper from connecting with other metals in the plating technology. The manufacturer deposits the electroless nickel on the catalytic copper surface. The oxidation-reduction reaction helps to achieve this. Therefore, this results in a layer whose thickness ranges between 3.0 to 5.0 microns.
Electroless palladium
This layer distinguishes ENEPIG from ENIG surface finish. Electroless palladium serves as a barrier layer. Also, the palladium prevents the corrosion of the nickel layer. It also prevents it from diffusing into the immersion gold. Furthermore, this layer serves as an anti-corrosion and anti-oxidation layer. An electroless reaction is commonly used for this layer deposition.
The electroless reaction makes use of a chemical oxidation reaction. Therefore, this nickel surface reacts with palladium and creates a thin layer. The manufacturer deposits the palladium on a layer with a thickness ranging between 0.05 to 0.1 microns. This depends on the application requirement.
Immersion gold
This is the last metallic layer of ENEPIG. Being the last layer, it offers low contact resistance. Also, it protects against friction and resists oxidation. Also, gold preserves the solderability of palladium. The immersion gold layer involves the immersion of the covered PCB. Manufacturers achieve this through a displacement reaction. In this process, palladium on the circuit board dissolves and discharges electrons. These electrons minimize the gold atoms surrounding the palladium.
Also, the gold ions attach to the PCB surface. This replaces some palladium ions. Therefore, there is a thin outer layer that has a thickness ranging between 0.03 and 0.05 microns. This is lower than any solution utilizing the gold plating process.
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What are the Benefits of ENEPIG?
ENEPIG has been around since the 1990s. Since then it has gained popularity among other surface finishes. There is a rising demand for this surface finish type. Therefore, the price of palladium has greatly reduced. Also, ENEPIG is a popular PCB surface finish due to the benefits it offers:
Durability
ENEPIG comprises multiple metallic layers which are corrosion-resistant. The ability to withstand corrosion prevents black nickel from occurring. Black nickel is the appearance of nickel corrosion. Also, the external surface of the ENEPIG finish is pore-free. This means that some corrosive elements can trap in the surface.
Low contact resistance
This is crucial in circuit boards to protect against overheating. Also, low contact resistance prevents poor grounding and energy loss. Therefore, ENEPIG finishes offer low resistance. This can be a result of the controlled deposition of gold, nickel, and palladium. Therefore, this makes the electrical resistance more uniform.
Affordability
Although there are more processing steps in ENEPIG finishes, it is cost-effective. It is more affordable than ENEG plating. This is because the cost of materials associated with ENEPIG is low. Also, ENEPIG deposits thinner layers of palladium and gold. Palladium was more expensive in the past. However, the reduced costs made it a budget-friendly material.
Longer shelf life
ENEPIG has a longer shelf life than other surface finishes. Gold and palladium don’t oxidize. Oxidization and tarnishing cause reduced solderability. Therefore, this reduced the overall quality of a finish. ENEPIG PCBs can stay untarnished irrespective of how long they are in storage. This is because of the palladium and gold shielding the finish.
Great solderability
ENEPIG provides great solder joint strength. The plating type matched with different alloys during soldering reflow. Also, it can tolerate multiple reflow soldering cycles.
Limitations of ENEPIG
ENEPIG has been around for more than ten years. Therefore, it has got its own limitations. Some of these limitations include:
Fractures
ENEPIG plating can be more vulnerable to fractures. This is a result of the brittleness of the palladium layers on top of the nickel.
Reliability
There are some problems when it comes to lead and tin bonding. ENEPIG experiences lead and tin bonding. The solder’s reliability will reduce if the palladium layer is very thick.
Cost
Although ENEPIG is more affordable, it is still expensive. This is because palladium and gold are precious metals. Therefore, they are quite expensive to use. The benefits of ENEPIG outweigh its limitations. Therefore, it is still a preferred option in the PCB industry.
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What is ENIG?
ENIG stands for Electroless Nickel Immersion Gold. It is also referred to as immersion gold or soft gold. The ENIG process is quite similar to ENEPIG. This process involves depositing Ni-P alloy on a Pd surface. Manufacturers use the displacement reaction to achieve this process. Also, they combine reduction and displacement reactions in the plating solution. The thickness of ENIG is always between 100 to 200µin. Also, the gold thickness ranges from 1 to 5 µin. A PCB with ENIG will have a golden yellow color. The gold color in ENIG is more than a gold-plated board. PCB users love the brighter surface.
Immersion gold forms a crystal structure. Therefore, it is easier to weld an ENIG surface than a gold-plated surface. This prevents solder joint failure. Also, the pads on ENIG PCB have nickel gold. Therefore, this won’t have an effect on signal transmission. ENIG finish offers a protection layer for the circuit board. Therefore, this minimizes oxidation.
ENIG PCBs feature nickel gold on the pads. This gold stays within the copper layer. Also, it doesn’t result in short circuits in fine pitch pads. ENIG comprises two layers of metallic coating. It features electroless plating coated with a thin layer of immersion gold. The immersion gold protects the nickel from any oxidation while in store. Also, the nickel acts like a barrier to the PCB surface and the copper.
Immersion gold is one of the most popular surface finish types in the PCB industry. This is because of its benefits. During the early stages of immersion gold plating, reliability was unclear. Therefore, this resulted in disjoining the copper pads from the finish.
The Processes Involved in ENIG Surface Finish
The ENIG PCB surface finish is a long process that involves several steps. Each of these steps requires careful monitoring to achieve the right finish.
Copper activation
Copper activation is crucial to making the copper layer active for the deposition of electroless nickel. Here, the circuit board goes through a cleaning process. This helps to get rid of oxidation residues and dust. Also, it helps to wet the surface to eliminate ant trapped air in the holes.
The manufacturer must carefully consider the micro-etching base. The best option is sulfuric/peroxide. Also, you need to monitor the operating temperature and the bath life. With proper rinsing, the residues will remove. Also, proper rinsing should be carried out before micro-etching. Oxidation can interact with the palladium catalysts deposits.
Also, it is advisable to remove any oxidation traces by using a catalyst pre-dip. The catalyst pre-dip also helps to acidify the PCB surface.
Electroless Nickel
This is the second step in the ENIG process. Here, the manufacturer uses nickel sulfate to produce sodium hypo-phosphite and nickel. This solution is a reducing agent. Also, the hypo-phosphate spreads the necessary electrons to minimize nickel ion. In addition, the exact temperature to enhance this reaction should be between 175 and 185°F.
Also, this helps the deposition of the nickel layer on the copper surface. Nickel functions as a barrier that prevents the copper from any reaction with other components.
Immersion Gold
This is the final step of the ENIG process. Here, oxidizing nickel to nickel ion generates electrons that enhance the reduction of gold in a solution. Also, these electrons minimize gold ions to a gold metal layer that shields the nickel. The thickness of the gold should be in line with the specific requirement.
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Advantages of ENIG Surface Finish
ENIG as a surface finish features a wide range of benefits. The benefits of this surface finish make it an ideal option in the PCB industry. Some of its benefits include:
Oxidation resistance
The ENIG layer protects the nickel surface from oxidizing. Therefore, this reduces the possibility of corrosion on the board. Also, this helps to increase the shelf life of the circuit board.
Great electrical performance
Immersion gold has great electrical performance. It helps to enhance electrical conduction among the PCB components. Also, this makes it a preferred option among manufacturers.
Environmentally friendly
This is one of the great benefits of ENIG. The immersion gold process doesn’t involve lead. The exclusion of lead in its process helps to reduce lead exposure. Lead is harmful to the environment as it emits some harmful substances to humans.
Prolonged shelf life
Also, ENIG can be in storage for 12 months. ENIG protects circuit boards from external defects like corrosion. Therefore, this makes it last longer than some surface finishes.
Flat surface
Manufacturers like to work on a flat surface. With a flat layer, manufacturers can easily assemble PCB components. For instance, ENIG is ideal for BGA mounting and flat chips.
High temperature-resistance
PCBs with ENIG finish feature good thermal diffusion. This helps them to resist extreme temperature conditions. Also, the ability to withstand high temperatures helps to enhance the functionality of the board. This means that the ENIG board can survive any environmental conditions.
Suitable for PTH
ENIG is suitable for plated through holes. This is because it offers a great solder surface. Therefore, this makes it easier to work on PTHs.
Versatility
ENIG PCBs are widely used for several applications. Its reliable performance and exact fitting make it ideal for use in many electronic products.
Limitations of ENIG Surface Finish
ENIG surface finish has several advantages. However, it has its own limitations. Some of which are:
High cost
The ENIG process is more expensive than other surface finishes. Immersion gold goes through a complex process. Therefore, it isn’t a budget-friendly option.
Signal loss
This is one of the pitfalls of ENIG. Immersion gold PCBs often experience signal loss when utilized for a long period. Therefore, this can have a negative impact on the performance of your device. This is not too ideal for applications that require signal integrity.
Black pad
Black pad is a common occurrence in ENIG. It results when phosphorus accumulates between nickel and gold layers. The immersion gold process uses a permutation reaction. Therefore, nickel might change to nickel ions if the nickel surface experiences more oxidation reaction.
Also, the bigger gold atoms will deposit irregularly to create a loose and rough arrangement. This means the gold layer might not cover the nickel layer completely. Therefore, this allows the nickel to come in contact with air. Finally, this will form nickel under the gold layer. This nickel rust will result in soldering failure. Black pad is a serious problem in ENIG.
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What is the Difference between ENEPIG and ENIG?
ENEPIG and ENIG are two surface finishes with differences. ENEPIG makes use of palladium while ENIG only uses nickel and immersion gold. The palladium layer in ENEPIG offers good electrical performance and oxidation resistance. However, ENIG is only ideal for use in low-end consumer electronics. ENIG only uses the immersion gold layer on the electroless nickel layer. ENEPIG features a layer of palladium between the gold and nickel layers.
Also, the ENIG surface finish doesn’t offer reliable fold wire bonding outcomes. This can be a result of the reduction in solder joint reliability. In addition, ENIG requires a proper process to prevent the corrosion of nickel. However, this is a common problem in ENIG surface finish.
The palladium layer covers the nickel layer. Also, this layer has low phosphorus content. Therefore, this helps to reduce the generation of black pads. Also, it eliminates the possibility of a black pad in ENEPIG. However, black pad is a serious problem in ENIG. Therefore, it is a serious concern for manufacturers that chose ENIG.
It is important to know that palladium is harder than gold. Therefore, it helps to improve the wire bonding capacity and solder reliability. Also, it improves antifriction. When it comes to reliability ENEPIG is a better option. Palladium minimizes the thickness of a gold layer. Therefore, this leads to a 60% reduction in cost compared to ENIG. ENEPIG is a cost-effective option.
Also, manufacturers can store ENEPIG for a period of 12 months. ENEPIG has a longer shelf life than ENIG. Also, ENEPIG can withstand multiple reflow cycles. However, ENIG has great heat dissipation capabilities. ENEPIG comprises palladium, which makes it more expensive than ENIG. When it comes to wire bonding ENEPIG is a more reliable option.
What are the Similarities Between ENEPIG and ENIG
Although these two surfaces’ finishes are different. However, they share some similarities. ENEPIG and ENIG both make use of electroless nickel and immersion gold. Both surface finishes feature a flat surface. This helps manufacturers to mount components on PCB surfaces easily. Also, ENEPIG and ENIG are both lead-free. This makes them an environmentally friendly option for PCB manufacturers.
ENEPIG and ENIG feature great electric performance and thermal diffusion. These two surface finishes have a relatively easy process. For instance, both surface finishes’ processes involve copper activation. This is the first step in their process. The surface passes through a catalyst bath that comprises palladium sulfate and sulfuric acid. With this bath, a basis for the deposition of the nickel and gold is formed.
Also, immersion gold is the final layer of the two surface finishes.
ENEPIG and ENIG provide a desirable and comprehensive solution for PCB plating. Also, the processes of these surface finishes require experience and skill. Therefore, an experienced PCB manufacturer can carry out these processes. These processes require careful monitoring and control.
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Factors to Consider When Choosing ENEPIG and ENIG
When choosing a PCB surface finish, you need to consider some factors. Not all surface finishes are suitable for your PCB requirement.
Application requirement
The requirement of your application will determine the surface finish you go for. If your application requires to function under high temperatures, ENIG is an ideal choice. This is because this surface finish has great resistance to high temperatures. It can survive extreme temperatures.
Cost
This is an important consideration. When cost is a factor, you can choose ENIG. ENEPIG is a more expensive option. This is because it involves the use of palladium.
Pad flatness
Some PCB surface finishes don’t yield even surfaces. This is not the case when it comes to ENEPIG and ENIG. These two surface finishes offer a flat surface. If you will need to mount more components on your PCB, ENIG or ENEPIG is a great choice for you. These finishes both offer even and thin layers.
Wire bonding capacity
When it comes to this, ENEPIG is an ideal option. Wire bonding capacity is an important factor when designing a circuit board. Also, ENEPIG has a highly reliable wire bonding capacity.
ROHS Compliance
Not all PCB surface finishes comply with the RoHS standards. This is because some surface finishes contain some toxic substances. ENEPIG and ENIG are both RoHS compliant. These surface finishes don’t contain lead. Hence, they are ideal for use.
Shelf life
The shelf life of a PCB surface finish is very important. ENEPIG and ENIG both have longer shelf life. These surface finishes can be in storage for up to 12 months.
Frequently Asked Questions
What does ENIG baking mean?
ENIG baking is a process that involves heating ENIG PCBs in an oven. The purpose of baking is to remove moisture from the PCB. Manufacturers do this before mounting components on the board. However, baking can damage your PCB if it isn’t properly done. Therefore, ensure you follow the right conditions when baking.
What affects the quality of ENEPIG plating?
Quality is important when plating a PCB with ENEPIG. The nature of the surface and the neatness of the surface will affect ENEPIG quality. A dry, neat, and smooth surface is important for ENEPIG plating.
Conclusion
ENEPIG and ENIG surface finishes are very reliable. These finishes adhere to the PCB quality standards. Also, the lead-free process makes these finished ideal options. Also, these two surface finishes provide manufacturers with a flat surface. Their processes, advantages, and limitations have been explained above. Also, we have compared these two surface finishes.
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