21/02/2025
PCB Surface finish
What is PCB Surface finish?
PCB (printed circuit board) Surface finish also called surface treatment,is a series of processing processes performed on the surface of the circuit board during the manufacturing process. The purpose is to protect the copper foil on the surface of the circuit board, enhance solderability, corrosion resistance, and provide good electrical performance.
Some of the most common surface finishes include HASL (hot air solder leveling), ENIG (electroless nickel immersion gold), OSP (organic solderability preservatives), Immersion Tin and Immersion Silver,ENEPIG(Electroplated Nickel Palladium Gold).
How to choose correct surface finish for PCB?
HASL(Hot Air Solder Leveling)
Process principle: Immerse the printed circuit board in molten tin-lead alloy (now there are lead-free types such as pure tin) to evenly cover the surface of the circuit board with a layer of solder, and then use high-pressure hot air to blow the excess solder flat, so as to form a relatively uniform solder layer on the surface of the circuit board.
Advantages: Mature process, low cost; good solderability, can adapt to various welding processes; good compatibility with subsequent assembly processes, and has been widely used in the industry for a long time.
Disadvantages: The consistency of solder thickness is difficult to accurately control, and there may be uneven thickness; due to the use of lead-containing solder (traditional process), it does not meet environmental protection requirements. With the increasingly stringent environmental 0regulations, it is gradually replaced by lead-free processes.
ENIG(Electroless Nickel Immersion Gold)
Process principle: A nickel layer is deposited on the copper surface by chemical plating.The nickel layer acts as a barrier layer to prevent copper atoms from diffusing into the gold layer, and then a thin gold layer is deposited on the nickel layer by replacement reaction.The gold layer mainly protects the nickel layer and improves solderability,corrosion resistance and good electrical contact performance.
Advantages: The surface is flat and can be adapted to PCBs perfectly;it has excellent solderability and corrosion resistance;the gold layer has good conductivity and is suitable for electronic products with high electrical performance requirements, such as mobile phone motherboards, high-end computer motherboards, etc.
Disadvantages:Compared with other surface finish,the cost is relatively high; the process control requirements are strict.If the parameters such as the composition of the plating solution, temperature, and time are not properly controlled, problems such as uneven phosphorus content in the nickel layer and inconsistent thickness of the gold layer are prone to occur, affecting PCB quality; there is a risk of "black pad" phenomenon between the nickel and gold layers, which is a defect that affects welding reliability.
OSP(Organic Solderability Preservative):
Process principle: A thin organic protective film is formed on the copper surface through chemical treatment.This protective film can prevent oxidation of the copper surface. During the PCB welding process, the protective film will decompose at high temperature, exposing the copper surface to good solderability.
Advantages: low cost, simple process;Protect the copper surface and prevent copper oxidation well during storage; environmentally friendly and in line with environmental protection requirements; flat surface, especially suitable for high-density, fine-line PCB manufacturing.
Disadvantages: The solderability retention time is relatively short, and the solderability will gradually decrease with the extension of storage time and the influence of factors such as environmental humidity; the requirements for PCB welding process are relatively high,and parameters such as welding temperature and time need to be strictly controlled.
Immersion Silver and Immersion Tin:
Process principle: A layer of Silver or Tin is deposited on the copper surface by chemical replacement reaction. The Silver/Tin layer can provide good solderability and corrosion resistance, and has good conductivity.
Advantages: Good solderability, can meet most welding process requirements; flat surface, suitable for fine lines; the conductivity of the Silver/Tin layer is second only to gold, and it can also be used in some occasions with high requirements for electrical performance; the cost is relatively low compared to chemical nickel plating gold.
Disadvantages: The silver/Tin layer is prone to discoloration (such as blackening due to sulfurization) in certain environments, affecting the appearance and solderability; there are certain requirements for the storage environment, and it needs to be stored in a dry, sulfur-free and other pollution-free environment.
ENEPIG(Electroplated Nickel Palladium Gold):
Process principle: First, electroplate a nickel layer as a barrier layer to prevent copper diffusion, then electroplate a palladium layer on the nickel layer, and finally plate a thin gold layer. The addition of the palladium layer enhances the corrosion resistance and solderability of the coating, while improving the adhesion to the gold layer.
Advantages: It has excellent corrosion resistance and solderability, and can adapt to various complex welding environments; the thickness of the gold layer can be precisely controlled, which is very suitable for occasions where the thickness of the gold layer needs to be precisely controlled to meet specific electrical performance requirements; it can effectively avoid the "black disk" problem and improve welding reliability.
Disadvantages: The process is relatively complex and the cost is high; various parameters need to be strictly controlled during the electroplating process, and the technical level of production equipment and operators is required to be high.
Choosing the right PCB surface finish is essential for ensuring the reliability and performance of a PCB. By understanding the different types of surface finishes available and their respective advantages and limitations, PCB designers and manufacturers can select the most suitable option for their specific application requirements.Xinfeng Huihe Electronic Technology Co.,Ltd have rich experience in surface finish,they can advise you a good choice while you are choosing surface finish.
Blog from:https://hhetech.com/blog/pcb-surface-finish/
