PCB Surface Finish Types & Comparison

07 Mar.,2024

 

ENEPIG

Electroless nickel electroless palladium immersion gold (ENEPIG) is another alternative for the surface coating of a PCB — it uses multiple layers to create a universal finish that can work with numerous applications, such as soldering or wire bonding with gold, aluminum and copper. ENEPIG is one of the more optimum choices for wire bonding as well as most PCB applications.

The order of the layers over the substrate corresponds to the name of this surface finish. Over a copper base is an electroless nickel layer. Atop that layer goes an electroless palladium coating. The palladium prevents the nickel from passing through to the gold layer on top. The final coating, an immersion gold layer, keeps the palladium from interacting with environmental contaminants that could otherwise impede soldering.

ENEPIG printed circuit boards were popular many years ago due to their overall board support and are now rising  once again thanks to a significant decrease in the cost of palladium. The design has been shown to successfully operate in conjunction with lead-free and eutectic solder alloys as well as most assembly processes.

ENEPIG vs. Other Finishes

ENEPIG is often referred to as a “universal” finish because it can be used for almost any PCB and in all assembly processes. Palladium completely dissolves during soldering so there is no oxide present in the nickel surface. This means your application has less probability of errors, and you can safely use it with varying solder applications.

Compared to other finishes, ENEPIG printed circuit boards will have a greater solder joint strength and are more likely to meet your industry requirements for overall PCB life and durability.

The advantages and disadvantages of ENEPIG are:

Advantages: The gold surface layer protects the PCB from tarnish and corrosion. The use of multiple layers inhibits corrosion from metal diffusion. Additionally, the composition of this finish provides a lead-free surface with a high solder strength while offering a more cost-effective option compared to electroless gold or electrolytic nickel gold. Lower contact resistance – The electrical resistance of this finish is uniform due to its production process and creates a situation where amperage is easier to predict and manage. Other advantages include:

  • Pore-free finish.
  • Significantly higher bond pull strength. High pull weights are maintained through multiple tests, making it especially suited to gold ball and aluminum wedge bonding.
  • Strong solderability thanks to nickel protecting and reducing copper dissolution.
  • Supports conductive adhesives for applications that do not need or may be harmed by solder.
  • Won’t tarnish, extending its useful life.

And perhaps the best news of all is that the ENEPIG process tends to provide significant savings over electrolytic nickel gold and electroless nickel or electroless gold.

Disadvantage: Due to the inclusion of palladium and gold, both precious metals, this surface finish may not be as cost-effective as options that do not use these materials. Additionally, the application of the multiple layers must follow careful procedures for success and good solderability.

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