Contents
What is ENEPIG?
PCB with a copper surface
In truth, the Electroless Nickel Electroless Palladium Immersion Gold (ENEPIG) is not a new surface finish.
The method surfaced previously but fell out of favor. In addition, Palladium was expensive, making ENEPIG a costly finish beyond most people’s budgets.
However, palladium is now more affordable, allowing ENEPIG to regain some popularity. Now, many manufacturers consider it the best option for wire bending.
But what is ENEPIG? It refers to a PCB metal plating process that attaches the board to a conductive surface.
Interestingly, ENEPIG has a reputation for being a universal finish. Why? Because it works with almost any PCB, and palladium can replace gold plating.
How do you Apply ENEPIG Surface Finish?
PCB with a gold surface
ENEPIG comprises four metal layers: nickel, palladium, copper, and gold. The process starts by activating the copper layer with a displacement layer.
This reaction causes the copper to act as a catalyst.
Then, adding nickel to the catalytic copper will merge the two materials.
This combination will protect the copper and prevent unwanted interaction with other metals.
The third process involves introducing a palladium layer for extra protection. Interestingly, palladium stops nickel from eroding and degrading the gold layer.
So, when using an electroless reaction, a chemical oxidation-reduction will occur, forming a thin layer of palladium and nickel.
Finally, immersing the board in gold completes the ENEPIG application process. And it’s because gold adds the ultimate protection while preserving the palladium.
Note: The gold layer will cover the entire board.
What is ENIG?
The electroless nickel immersion gold (ENIG) metal finish consists mainly of two layers. One has a gold composition, while the other typically uses (electroless) nickel.
Incidentally, you may also encounter PCB manufacturers and professionals who refer to ENIG plating simply as immersion or chemical gold.
The gold layer protects the nickel from oxidation.
Manufacturers deposit the gold onto the nickel layer using a technique referred to as quick immersion. Essentially, the manufacturer dips the nickel layer in a solution mainly of gold salts.
This process is what primarily makes ENIG different from ENEPIG. But how are these plating methods similar?
Similarities Between ENIG and ENEPIG
The main similarity between ENIG and ENEPIG is that they utilize the same base materials – electroless nickel and immersion gold. Incidentally, they’re lead-free and offer a smooth, flat, firm finish, allowing manufacturers to solder components onto PCBs with less difficulty.
Moreover, thanks to their lead-free compositions, most experts consider them less harmful to humans and the environment than lead-based surface finishes like HASL.
Another similarity between ENIG and ENEPIG is that they both use copper activation.
The surface passes through a catalyst bath of palladium sulfate and sulfuric acid during this process. This makes it easier to deposit the nickel and gold material.
ENIG vs. ENEPIG: What’s the Difference?
The palladium layer is the significant addition that differentiates ENEPIG from ENIG.
In other words, Electroless Nickel Immersion Gold doesn’t include palladium between the nickel and gold layers.
However, ENIG still provides solid electric performance, including oxidation and temperature resistance.
Moreover, ENEPIG is more reliable for gold wire bonding, as ENIG often reduces solder joint reliability. ENIG is also unsuitable for touch contact points.
Advantages of ENEPIG
Generally, ENEPIG is more cost-efficient than other hard or soft gold plating alternatives. Gold is currently more expensive than palladium, making the ENEPIG more affordable.
Interestingly, it contrasts the surface finish’s initial release as more individuals and businesses can use ENEPIG plating.
In addition, ENEPIG offers an attractive, thin finish.
The layer from the electroless reaction between the palladium and nickel is usually not higher than 0.1 microns.
Thankfully, this layer thickness is ideal for many boards.
ENEPIG protects the PCB and makes it easier to work with other elements. Also, the surface finish makes soldering more reliable and easy.
And it reduces the amount of soldering required on a board.
In addition, ENEPIG plating doesn’t degrade. Hence, you’ll enjoy an increased PCB shelf life.
Disadvantages of ENEPIG
ENEPIG is not without its setbacks. Although this technique is now more affordable, ENEPIG is still one of the most expensive surface finishes. Also, Palladium and gold are precious metals, making them costly.
In addition, you may experience reliability issues with an ENEPIG finish, particularly when manufacturers don’t maintain chemistry.
For example, copper and palladium can reduce a PCB’s lead and tin bonding integrity.
More importantly, incorrect use of an ENEPIG coating can cause fractures. It’s because the layers above the nickel plating are often brittle.
Additionally, an excessively thick palladium later will dampen solder reliability and performance.
Factors to Consider When Choosing Between ENIG and ENEPIG
Since these surface finishes are very similar in their compositions and appearance, it can be sy to pick between the twothemer, they’re not completely identical and thus may be more suitable in some applications than others.
To decide which one will meet your requirements best, you need to consider the following factors:
Surface and Pad Flatness
This is another aspect where both ENIG and ENEPIG perform similarly. It’s one of the very reasons manufacturers prefer these surface finishes.
They offer a uniform, smooth coating, allowing manufacturers to install additional components.
Shelf Life
Shelf life describes how long you can store the surface finish before it spoils. Fortunately, both ENIG and ENEPIG have relatively long shelf lives.
You can store them for as much as a year before using them. Consequently, both surface finishes are tied in this aspect.
Wire Bonding Capacity
Wire bonding describes joining conductive wires to substrates and semiconductor chips.
It allows manufacturers to form electric interconnections between electronic components.
The wire bonding capacity describes how well these interconnections can form and how efficiently they can pass electric signals.
Thanks to its use of electroless palladium, the ENEPIG surface finish has a far better wire bonding capacity than the ENIG surface finish.
Cost
The ENEPIG surface finish’s inclusion of electroless palladium makes it perform better than ENIG. However, because of its use of this material, it also costs more.
If you’re worried about cost, consider selecting an ENIG surface finish for your PCBs as it is typically cheaper.
Application Requirements
An ENEPIG surface finish would be your best bet in applications requiring fast connection speeds.
However, there is one aspect where ENIG surface finishes outdo their ENEPIG counterparts. For instance, ENIG surface finishes tend to display better thermal resistance.
As such, ENIG is more suitable for use under high temperatures than ENEPIG.
Restriction of Hazardous Substances (RoHS) Compliance
The RoHS regulates what chemicals and materials manufacturers can use to fabricate electronics.
It determines the amount or volume of hazardous chemicals manufacturers can use per item.
For instance, manufacturers must use less than 1000 parts per million (PPM) by lead weight to be RoHS compliant.
As we previously mentioned, both surface finishes are completely lead-free.
As such, we can consider them both completely RoHS compliant, making them safe for manufacturers.
Once again, both surface finishes are equal in this aspect.
Closing Words
PCBs using multiple layers will benefit more from ENEPIG coatings.
Also, ENEPIG can satisfy all additional requirements for PCB designs with differing packing technologies.
In addition, ENEPIG is less expensive than hard gold and can accommodate touch contacts without causing problems.
Interestingly, ENEPIG’s superior quality often creates medical, military, and aerospace PCBs. So, ENEPIG is your go-to if you require push contacts or wire bonding.
Do you have any questions? Feel free to contact us, and we’ll be happy to help.
