PCB Manufacturing

The Ultimate Guide to Understanding ENIG Thickness in PCB Manufacturing

ENIG Thickness in PCB Manufacturing

Every detail matters while manufacturing printed circuit boards. The Thickness of Electroless Nickel Immersion Gold (ENIG) coating on the board is one of the important factors that has to be taken into consideration during the process. To manufacture PCBs with extraordinary performance, quality, and reliability as well as to reduce the cost of PCB fabrication, it is essential to fully understand the ENIG thickness values. In this topic, we will have to go in-depth and learn about the ENIG thickness value, its significance and the factors that affect its performance.

Why ENIG?

ENIG is widely used in all kinds of PCBs because of its excellent properties like good solderability, flat surface finish, cost-effectiveness, high reliability, suitability for high-density connections and corrosion resistance. It is a metallic surface finish with gold (AU) plated over a thin layer of nickel (NI). This two-layer construction provides solid electrical connections and provides requisite protection. Fig below shows the process of ENIG coating in manufacturing.

ENIG Process

ENIG coating involves the above steps during manufacturing, starting from cleaning the surface of the PCB board to get rid of any contaminates or the copper for oxidation caused due to environmental effects. After cleaning, PCB boards are prepared for nickel plating using a catalyst process and the surfaces are then ready for coating. A thin layer of Nickel is plated over the copper surface using an electroless method and the boards are rinsed to clean the surface to make it prepare for further processing. It is followed by immersion in gold layer deposition to coat a thin layer of gold over nickel and finally, the boards are rinsed again to clean the surface and dried to get a smooth & finer finish.

Significance of ENIG thickness:

A proper ENIG thickness is vital in PCB manufacturing. The amount of ENIG thickness coated on the surface determines, how the boards function under different environments. Let’s see why it is important:

  • Good Solderability
    During the assembly process, an ideal ENIG thickness ensures the proper soldering of components, facilitating the solder to form strong joints. Inadequate thickness would lead to poor solderability and would cause the components to barely have a connection, which in turn reduces the performance and the quality of the board.
  • Corrosion resistance
    Copper if exposed to oxygen and moisture in the air, forms copper oxide resulting in corrosion. Over time it leads to signal delay and electrical resistances. To avoid this ENIG acts as a protective layer against environmental factors like moisture and oxidation. A proper amount of ENIG coating ensures long-term corrosion resistance and provides the board with a durable surface finish.
  • Surface flatness
    Due to the presence of a thin layer of gold coating over nickel, it provides an excellent flat surface which aids in soldering and installing the components effectively. Ensuring proper thickness throughout the board reduces uneven solder joints and provides uniform soldering.

Factors impacting the ENIG thickness

ENIG (Electroless Nickel Immersion Gold) is a type of metallic surface finish used in the PCB industry. It consists of a thin layer of gold plated over nickel on the exposed copper surface. The nickel acts as the barrier between the copper and gold, thus preventing the diffusion of copper into the gold layer which compromises the solderability. The gold layer provides a flat and solderable surface for component placement. Typically, Nickel value ranges from 2 to 6 microns and gold value ranges from 0.05 to 0.1 microns.

Several factors influencing the ENIG thickness coating are as follows:

  • Processing methods
    ENIG coating on the board is greatly affected by the immersion time, temperature and the plating bath composition. To achieve the finest surface on the board, it is necessary to fine-tune all of the above factors during manufacturing.
  • Substrate material
    ENIG coating is influenced by the construction and surface properties of the substrate material used. Different materials require different adjustments during the deposition process to get the ideal thickness.
  • Panel utilization
    The amount of ENIG thickness throughout the PCB varies as the layout utilization of PCB panels. Even a small change in trace width and copper density may result in a variation in ENIG thickness value. To achieve uniform coating throughout the board, utilization of the panel during the design process has to be taken into consideration.
  • Quality control strategies
    Effective quality control procedures must be in place to monitor the ENIG thickness values within the specified tolerances. Regular inspection helps in identifying the deviation in thickness value and ensuring uniform thickness throughout the production process.

PCB with ENIG Surface Finish

Impacts of ENIG Thickness on PCB Manufacturing

As we have mentioned above, the thickness of ENIG is Nickel around 2-6 microns and gold around 0.05-0.1 microns. Within this range, we can get a perfect ENIG surface finish, and get qualified PCBs. So getting proper ENIG finish thickness is very important in the PCB manufacturing process, main impacts as below.

  • Flat surface
    Gold layer in the ENIG protects nickel from oxidation and provides an excellent flat surface on boards which will ease the soldering process. A flat surface provides excellent bonding for BGA and SMD components during soldering. This reduces the possibility of solder bridging and inadequate soldering and produces uniform solder joints throughout the board.
  • Excellent solderability
    Nickel acts as a barrier between the copper and gold layer preventing the diffusion of copper into the gold layer which could compromise the solderability of the components. Since gold is a good conductor of electric current, coating a thin layer of gold over nickel provides a strong metallic bond to provide reliable solder joints on the surface. Hence, ENIG is one of the widely used surface finishes by most PCB fabricators throughout the world due to its excellent solderability properties.
  • ROHS compliant
    ENIG finish complies with ROHS (Restriction of Hazardous Substances) since it can be used with both leaded and lead-free soldering process. Because of its flexibility, manufacturers can adapt to changing environmental regulations without affecting the durability or solderability
  • Longer shelf life
    Compared to other surface finishes ENIG finished PCBs have a longer shelf life of 12 months or more without getting affected by substantial oxidation.
  • Withstand several times reflow cycles
    ENIG is suitable for multiple soldering processes since it is capable of withstanding numerous reflow cycles without degrading.
  • Reduced risk of defects
    ENIG surface minimises the solder bridges and improves the electrical connection. As a result, it reduces the need for rework and provides first pass yields most of the time, eventually improving production efficiency and lowering the cost.
  • Reliability
    Performance of the electronic equipment heavily depends on the solder joints of the components over the long run. The superior solderability of ENIG finish lowers the risk of solder connection failures caused by temperature changes, mechanical stress, or environmental variables, thereby enhancing the overall dependability of PCB assemblies.

Conclusion

In summary, Due to its excellent solderability and surface flatness properties ENIG surface has a significant impact on the PCB manufacturing process. Its reliable solder joints, compatibility with ROHS compliances and reduced defect rates make it a suitable surface finish to consider during the manufacturing of reliable electronic products.

ENIG thickness is a crucial part of the PCB manufacturing process, which influences the solderability, corrosion resistance and signal integrity. Understanding the significance of ENIG thickness and the factors that influence it allows manufacturers to improve product quality and achieve the finest flat surface.

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