The manufacturing of printed circuit boards has to do with several technologies. This helps in bringing the functionalities and desired results to reality. The surface finish is one of such technologies. A PCB’s copper layer undergoes oxidation whenever it comes in contact with air. With this, it reduces the copper’s ability to solder. Surface finishes help in protecting the copper layer from oxidation, thereby maintaining the material’s electrical performance and soldering.
There are different surface finishes for application. Each of these finishes elicits different results and works fine for several applications. ENEPIG plating is one of such finishes for printed circuit boards. The full meaning of ENEPIG is Electroless Nickel Electroless Palladium Immersion Gold. The ENEPIG finish offers many benefits, which makes it appropriate for different applications.
What Does ENEPIG Mean?
ENEPIG is simply described as metal plating for printed circuit boards. It came to be about ten years ago, and recently, has gained wide recognition due to its low cost in contrast to those of other PCB gold plating types.
Over the last several years, palladium prices have decreased substantially in contrast to gold. The use of palladium plating in your printed circuit boards rather than pure gold, services dealing in PCB plating will be able to reduce costs associated with plating. This will make the ENEPIG plating solution even more popular.
The ENEPIG plating is also called “universal surface finish”. This is due to its ability to get deposited on any printed circuit board assembly. Primarily, ENEPIG finishes are useful in supporting soldering, as well as aluminum and gold Enepig wire bonding. Asides these functions, ENEPIG plating extends a plated PCB’s functional shelf life well over a year.
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ENEPIG: How Does it Work?
ENEPIG has to do with the deposition of four metal layers on surfaces of printed circuit boards. These are gold, palladium, nickel, and copper. Any process involved in the creation of ENEPIG surface finishes includes these steps.
Copper Activation
For this step, the activation of copper layer requiring protection holds. This determines the pattern of deposition in the step of electroless nickel plating. You can accomplish this process by making use of a displacement reaction that makes this copper layer serve as a form of catalytic surface.
Electroless Nickel
The nickel layer here serves as a barrier. This prevents copper from having any interaction with other metals necessary for the plating technology, most especially gold.
This layer is placed on the surface of the catalytic copper making use of the Redox reaction. What results is a layer that has a thickness of about 3.0 to 5.0 microns.
Electroless Palladium
Here, the palladium layer helps in differentiating the ENEG from the ENEPIG surface finish. This serves as a second barrier layer. With palladium, you can prevent the nickel layer from corroding, as well as diffusing to the gold layer.
Also this layer serves as an anti-corrosion and anti-oxidation. You can achieve the deposition of this layer, similar to nickel, with the help of an electroless reaction that utilizes a Redox reaction. This causes the reaction of the nickel surface with palladium and results in a thin layer.
Immersion Gold
The final layer, which you add to the ENEPIG surface, is gold. This lends the advantages of oxidation resistance, friction protection, and low contact resistance. Also, gold helps in preserving the solderability of palladium.
From the name, the services of immersion gold plating immerse your covered PCB completely. It achieves this utilizing a displacement reaction where the PCB palladium dissolves, and also releases electrons reducing the gold atoms that surround it. These gold ions go on to attach to the PCB’s surface, thereby replacing some of the palladium ions. This leads to a very thin outermost layer with thickness falling between 0.03 to 0.05 microns. This is substantially different compared to other solutions making use of techniques involved in gold plating.
Why Plate PCBs Utilize ENEPIG?
The printed circuit boards of today keep advancing, thereby leading to lighter, smaller electronics, which maintains maximum speed and functionality. To help in improving functionality, as well as maintaining the PCB’s structural integrity, the plating of pcbs using metallic finish is now very important.
Out of the available plating options, ENEPIG offers the highest number of advantages, whilst keeping material and processing costs at a low. Asides from this, it offers more benefits compared to other finish options such as ENIG, ENEG, and silver plating, including great anti-corrosive, durability, and solderability properties.
The above benefits are not just significant with respect to consumer electronics. They are also useful in different industries. With ENEPIG finishes, you will maintain the reliability and high functionality of your printed circuit board. This will make it a perfect finish for any application requiring reliability as a priority. Some examples here include medical, military, aerospace, and automotive.
Comparing ENEPIG with ENEG and ENIG
In today’s PCB plating, there are three main electroless processes. We’ve talked about the first, which is ENEPIG. The remaining two are ENEG – Electroless Nickel Electroless Gold and ENIG – Electroless Nickel Immersion Gold. Out of these three, ENEPIG is the lowest with respect to cost, and most popular. Let us consider other striking differences between the three processes.
ENEG
This plating usually delivers a better wire bonding compared to that of ENIG. Moreover, one major issue of this plating type has to do with the cost. The electroless gold layer’s thickness is higher compared to the other options listed.
Gold has been increasing in price of late, which has led to the record high process for ENEG plating. Furthermore, the process of the electroless gold seems more complex than that of the immersion gold. This has also led to increases in materials and labor costs.
Asides from being expensive, the gold thick exterior of ENEG plating reduces the reliability of the solder joint. This reduced reliability is as a result of problematic interactions between gold and tin, thereby producing less-stable intermetallics.
ENIG
This process is relatively easy. Virtual wise, it shares great similarities with ENEPIG. The only difference here is that it relinquishes the layer of palladium between the layers of immersion gold and electroless nickel. It offers good electric performance and oxidation resistance. Asides from this, it is temperature resistant and provides great properties for thermal diffusion.
However, surface finishes made with ENIG Enepig are only used in consumer products (low-end). This is because of their issues regarding quality. For beginners, surface finishes of ENIG Enepig usually don’t offer efficient results of gold wire bonding. This could be due to the interaction between gold and tin, which produces intermetallics with problems, leading to a reduced reliability in solder joints.
In addition, it is necessary to work with proper processes. This is necessary to avoid any nickel corrosion. This problem is a common one for any solder joints on ENIG finishes.
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Comparing ENEPIG with other Plating Solutions
Asides the other plating solutions we just discussed above, there are other PCB finishes, which are usually utilized to ensure lead-free results.
Compared to ENEPIG, they are much more different compared to the ENIG and ENEG plating. These include immersion silver, immersion tin, and organic solder preservatives. Let’s consider each of them closely.
Immersion Silver
This is another finishing material used as a PCB cover. In Particular, engineers prefer immersion silver due to its electrical testing and beautiful finish. It also boasts of a great shelf life, and it is corrosion-resistant.
However, it doesn’t work best for soldering. Also, it bonds weakly to gold wiring leading to solder joints that are weak. This weakness is obvious from the interfacial micro-voids, which show up in the material. Furthermore, it could tarnish under some conditions, which could result in more soldering problems.
Immersion Tin
Normally, tin is a well-known plating material. PCB engineers love this due to its ability to reliably form solder joints using tin. However, the material fails to bond properly with others, most especially gold. It is susceptible to whiskering anytime surface mounting is on. This could lead to failure of the PCB.
Asides from this, immersion tin has a high corrosion risk after the assembly. Plating with tin immersion leads to a product having just 3 to 6 months as its shelf life. This is much shorter compared to other methods of plating.
Organic Solder Preservatives
This is also called OSP. This finishing method makes use of organic compounds (water-based) for coatings. The use of OSP results in reliable joints. However, their performance seems to suffer once the reflow number increases.
Also, their coatings seem to be short-lived. They don’t last up to a year as a result of the corrosion risks associated with after assembly. In addition, they also provide poor substrates for test probes. Therefore, you must conduct the testing during the assembly before you begin the process of plating.
None of these options are perfect. You will find issues linked to capabilities of wire bonding, shelf life, and reflow cycle. Comparing these options with ENEPIG, ENEPIG provides a more beneficial solution, with a great performance reliability and long shelf life. ENEPIG wire bonding is also great.
What Benefits does ENEPIG Offer?
Since the creation of ENEPIG came late in the 1990s, it has grown slowly as an option for plating. It has even seen a recent popularity surge resulting from reduction in prices of raw palladium. Furthermore, this method is popular as a result of its great benefits.
Cheaper
Though there are high costs involved in the processing of ENEPIG finishes, generally, it is cheaper compared to the electrolytic gold/electrolytic nickel plating. Primarily, this is due to the reduced costs of material for ENEPIG plating in contrast to plating using ENEG. The latter requires gold deposits that are relatively thick, while ENEPIG requires thinner layers of palladium and gold.
Great Solderability
The final plating of ENEPIG provides great strength for the solder joint. This type of plating works with different alloys during the reflow soldering exempting lead, and has the ability to withstand many reflow cycles of soldering without any degrading.
Contact Resistance is Low
This feature is very important for printed circuit boards. This prevents poor grounding, energy losses, and overheating. With ENEPIG finishes, you can be sure of low resistance due to the deposition of gold, palladium, and nickel, thereby making the plating’s electrical resistance more uniform.
Durable
ENEPIG finishes have multiple layers, which are resistant to corrosion. This is because palladium and gold have anti-corrosive features. This resistance to corrosion prevents black nickel from occurring. The ENEPIG finish’s outer surface is pore-free and smooth. This means the trapping of more elements that are corrosive on the plating’s surface, and then eat away right there.
Protective Barriers
ENEPIG finish has both palladium and nickel. These serve as layers of barrier that prevents tin from affecting the copper in solder. With these barriers, the solderability is greatly improved. Also, they prevent the mixing of copper with gold, which may affect conductivity.
Very Long Shelf Life
Unlike several other options for plating like aluminum, copper, and silver, gold and palladium don’t oxidize or tarnish. These conditions occur as a result of exposure to humidity and air. Both condition lead to reduced solderability, as well as overall reduction in the quality of the finish. Also, with time, both finishes worsen. However, with palladium and gold helping out to protect your finish, your Enepig PCB will stay untarnished regardless of the length of time they stay in storage.
Conclusion
ENEPIG plating provides you with a desirable and comprehensive solution for your needs and also requires a plating crew with vast experience to execute the process. If you believe that ENEPIG is the best for you, then make sure you choose the best company to offer this service.
RayMing PCB boasts of having vast experience concerning electronic plating, which includes ENEPIG technology. We at RayMing have been offering solutions for metal finishing for a while now. We are also involved in ENEPIG PCB manufacturing. Contact us today and get the best value for your money!
