When exposed to air, the outer copper layers of a printed circuit board (PCB) will naturally oxidize, reducing their ability to be soldered effectively. To prevent this oxidation and maintain the solderability and electrical performance of the copper surfaces, manufacturers apply various surface finishes. These finishes act as protective layers that shield the copper and preserve its functionality.
At Stream PCB, we offer a range of surface finishes tailored to specific application needs, with ENEPIG (Electroless Nickel Electroless Palladium Immersion Gold) being one of the most popular options. This finish offers numerous benefits and makes the PCB suitable for a variety of applications.
ENEPIG is a metal plating process for PCBs that has gained significant popularity over the past few decades due to its relatively low cost compared to other plating methods. The drop in palladium prices over the years has led many manufacturers to use palladium as an alternative to pure gold, which helps lower plating costs even further. This has boosted the adoption of the ENEPIG process in the electronics industry.
Known as the Universal Surface Finish, ENEPIG can be applied to nearly any PCB surface. This finish is particularly useful for soldering and bonding with aluminum and gold wires, and it helps extend the functional shelf life of a PCB beyond one year.
The ENEPIG finish involves a four-layer metal deposition process on the PCB surface: copper, nickel, palladium, and gold. The steps to create an ENEPIG finish are as follows:
This step selectively activates the copper layer, making it ready for the subsequent nickel plating. A displacement reaction causes the copper to act as a catalytic surface.
A nickel layer is deposited through an oxidation-reduction reaction. The nickel serves as a barrier, preventing the copper from interacting with the following metal layers. The thickness of the nickel layer typically ranges from 3 to 5 microns.
Palladium is added as another protective barrier. It prevents nickel from diffusing into and corroding the final gold layer. The palladium layer is also deposited through an electroless process and typically has a thickness of 0.05 to 0.1 microns.
The final gold layer is applied through immersion plating. The immersion process reduces palladium and replaces some of it with gold, resulting in a thin, corrosion-resistant gold layer of about 0.03 to 0.05 microns in thickness.
The widespread popularity of ENEPIG can be attributed to the many advantages it offers:
While the ENEPIG process involves several steps, it is still more cost-effective compared to other methods like electrolytic nickel/electrolytic gold plating (ENEG). Palladium’s reduced cost and the thinner gold layer contribute to keeping overall costs low.
The multi-layer plating of ENEPIG creates a highly corrosion-resistant surface, thanks to the anti-corrosive properties of the gold and palladium layers. The smooth, pore-free surface also helps prevent the accumulation of corrosive elements.
ENEPIG provides excellent solder joint strength. It works well with lead-free solders and can withstand multiple reflow soldering cycles without degrading. The palladium layer dissolves during soldering, creating an oxide-free nickel surface for stable solder connections.
ENEPIG plating enhances the bondability of both aluminum and gold wires, offering excellent support for wire bonding under long-term stress.
ENEPIG reduces contact resistance, which helps improve grounding, minimize heat, and reduce energy losses. The even deposition of nickel, palladium, and gold contributes to this reduced resistance.
Both the nickel and palladium layers in the ENEPIG finish act as protective barriers, preventing solder tin from interacting with the copper. These barriers improve solderability and protect the copper from being compromised.
In some applications, conductive adhesives are used instead of solder for attaching components to the PCB. ENEPIG provides excellent support for these adhesives.
Unlike other surface finishes that are prone to oxidation and tarnishing, ENEPIG’s gold and palladium layers remain stable and do not oxidize, even when exposed to air and humidity. This allows PCBs with ENEPIG finishes to retain their original quality and solderability, even after extended storage periods.
If you’re considering ENEPIG plating for your next PCB project, Stream PCB is here to help. We have extensive experience in providing plating services, including ENEPIG, and can help you determine the best solution for your application.
With our expertise in plating techniques, including immersion gold plating, palladium plating, and ENEPIG, we offer tailored solutions that meet your business requirements and keep your costs low. Trust us to help you achieve the best results for your PCBs.
ENEPIG (Electroless Nickel Electroless Palladium Immersion Gold) is a surface finish that provides excellent solderability, durability, and anti-corrosion properties to a PCB. It is widely used for its reliability and long-term performance.
ENIG (Electroless Nickel Immersion Gold) is similar to ENEPIG but lacks the critical palladium layer between the nickel and gold layers. This absence makes ENIG less reliable, as it allows tin and gold to interact, leading to the formation of problematic intermetallic compounds. Additionally, ENIG does not prevent nickel corrosion, a feature that ENEPIG's palladium layer provides.
ENEG (Electroless Nickel Electroless Gold) offers better gold wire bonding than ENIG, but the gold layer is much thicker, increasing costs. This thicker gold layer also negatively impacts the reliability of solder joints. ENEPIG, in contrast, uses a thinner gold layer while offering better protection and reliability through the palladium layer.
ENEPIG offers superior corrosion resistance, a long shelf life, and reliability while overcoming the drawbacks of these alternatives.
The palladium layer in ENEPIG prevents nickel from corroding and reacting with the gold layer, which improves the solder joint's reliability. Additionally, ENEPIG’s gold layer is much thinner than other finishes, further reducing costs while maintaining performance.
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