A PCB is also called a copper-clad board, emphasizing the significance of copper in PCB construction. Copper provides excellent electrical conductivity, processability, and corrosion resistance to the circuit. However, a noteworthy issue is the tendency of copper to oxidize in the air, affecting its solderability. While a bare copper board exists, it requires assembly to be completed within two hours after unsealing, making it less common. To address these issues, PCB surface finish is often employed. In projects with higher shelf-life requirements, ENEPIG and ENIG are the most commonly used methods. In this article, TechSparks will compare the pros and cons of these two treatment methods to help determine which one is more suitable for your project!
Concepts of ENEPIG and ENIG
ENEPIG and ENIG are two surface finish methods that use deposition techniques to form metal layers on the surface of PCB. They have made significant progress in improving soldering uniformity and reliability. ENEPIG can be considered an evolved version of ENIG, providing us with more enhanced performance.
ENIG stands for Electroless Nickel Immersion Gold. Its working principle involves sequentially depositing nickel and gold layers on the surface of the PCB. This process aims to provide a smooth, solderable surface, significantly improving soldering uniformity and reliability. Compared to other surface treatment techniques, ENIG, using metallic materials, offers better electrical conductivity and corrosion resistance, making it a longer-lasting surface treatment technology. In this process, chemical nickel directly contacts the PCB, providing a solid substrate for the surface, while the gold layer provides high oxidation resistance, effectively preventing oxidation on the PCB surface.
On the other hand, ENEPIG, or Electroless Nickel Electroless Palladium Immersion Gold, introduces a palladium layer between the nickel and gold layers on the basis of ENIG. This palladium layer serves as a barrier, effectively preventing the diffusion of nickel and palladium, preventing nickel from diffusing upward to the gold layer.
Principles for Choosing Surface Finish
In the rapidly evolving technological landscape, manufacturers offer various types of PCB surface finish solutions. Each approach has its unique advantages and applications. For example, cost-effective HASL may be preferred in consumer electronics, while high-performance requirements in the industrial sector might lead to choices like ENEPIG and ENIG. Here are general principles for making a selection:
- Is it within the project budget?
- Does it suit the specific environment where the product will be stored?
- Does it adhere to environmental regulations?
- Does it support multiple soldering and rework cycles?
- Does it provide good solderability and wetting properties?
- Is it suitable for high-density circuit layouts?
- Does it have a longer shelf life?
- Is it required to have high flatness?
- Does it need to bond with gold or aluminum wires?
When specifically comparing ENEPIG and ENIG, we also need to consider their performance in various aspects such as high-frequency applications and long-term reliability. Now, let’s evaluate whether ENEPIG or ENIG is more suitable for your project based on these principles.
Pros and Cons of ENEPIG and ENIG
Avoiding White Etching and Black Pads
Meeting the Requirements for Multiple Soldering
High Wire Bond Pull Strength, 10g for Aluminum Wire, 8g for Gold Wire
Suitable for Conductive Adhesives
More Favorable for High-Performance Devices
Applicable to Various Electronic Products and Micro Packaging
Complies with All RoHS Requirements
Low Reactivity of Gold Metal Provides Superior Corrosion Resistance
No Need for an External Power Source for Electroplating, Simplifying the Process
Metal Materials Offer Superior Electrical Performance
Forms a Uniform and Smooth Surface to Facilitate Soldering
Minimum Shelf Life of 12 Months
Compatible with Electrical Test Probing
Introducing Additional Processes Increases Complexity.
Extra Palladium Layer Results in Poorer Solderability.
Fragility of the Palladium Layer May Lead to Mask Fractures.
Being the Most Expensive Surface Finish Option.
Difficult Rework When Failures Occur.
Metal Diffusion May Cause the Occurrence of Black Pads in ENIG.
Nickel’s Higher Resistance Makes It Unsuitable for Projects Requiring High-Speed Signals.
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