In the PCB manufacturing process, selecting the appropriate surface finish is crucial to the performance and reliability of the circuit board. Among these, Electroless Nickel Immersion Gold (ENIG) and Hard Gold Plating are the most common surface treatment methods.
So, what exactly are the differences between the two? Let's delve into their distinctions from the following aspects:
1.Process Principle
ENIG: Deposits a layer of nickel and gold on the copper surface of the PCB through a chemical reaction. The nickel layer acts as a barrier to prevent copper diffusion, while the gold layer enhances solderability and oxidation resistance.
Hard Gold Plating: Uses electroplating technology to directly attach a layer of metallic gold to the copper surface of the PCB. The plating is thick and hard, typically used in areas requiring high wear resistance.
2.Process Sequence
ENIG: The ENIG process is usually carried out after solder mask application, similar to immersion tin, where a gold layer is deposited on the exposed copper surface through a chemical method.
Hard Gold Plating: Hard gold plating must be completed before the solder mask is applied, as the electroplating process requires conductivity, with the PCB acting as an electrode to form a circuit with the plating tank. If the solder mask is already in place, the current cannot pass through, making plating impossible.
3.Soldering Performance
ENIG: Also known as soft gold, it has a uniform and soft gold layer, providing high solder joint reliability and better solderability than Hard Gold Plating. It is suitable for soldering most electronic components.
Hard Gold Plating: Also known as hard gold, its soldering performance is slightly inferior to ENIG, with a higher likelihood of soldering issues, making it unsuitable for applications requiring high solderability.
4.Wear Resistance
ENIG: It has relatively low wear resistance. Due to the thin (usually 1-3 microinches) and soft gold layer, it is not suitable for areas that require frequent mechanical contact or friction.
Hard Gold Plating: It has high wear resistance. The gold layer is thicker (up to several tens of microinches) and harder, capable of withstanding frequent mechanical contact and friction, making it widely used in areas like gold fingers and connectors.
5.Oxidation Resistance
ENIG: The gold layer is relatively thin and is mainly used to improve solderability and oxidation resistance, but its oxidation resistance is not the strongest.
Hard Gold Plating: With a thicker gold layer, it offers excellent oxidation and corrosion resistance, making it more suitable for applications exposed to harsh environments over the long term.
6.Color
ENIG: This process covers a thin layer of gold by chemical deposition, forming a golden surface that is more yellow than gold plating.
Hard Gold Plating: It uses the principle of electroplating to deposit a thick and hard layer of gold with a different crystal structure. The final surface treatment is slightly white, almost similar to the color of nickel.
7.Cost
ENIG: With a thinner gold layer, the overall cost is lower, making it the preferred surface finish for most standard PCBs.
Hard Gold Plating: Due to the thicker and harder gold layer, the cost is higher and is typically used in specific high-end and wear-resistant applications.
