PCB surface treatment is a critical step in the manufacturing of printed circuit boards. It involves applying a thin layer of material to the surface of the copper traces and pads on the PCB. There are several common types of PCB surface treatment, each with its own characteristics and purposes.

　　One of the most widely used surface treatments is hot air solder leveling (HASL). In this process, the PCB is dipped into a molten solder bath and then passed through a hot air blower. This creates a thin, smooth layer of solder on the copper surfaces. HASL provides good solderability and is relatively inexpensive. However, it may have some limitations in terms of flatness and thickness control, especially for fine-pitch components.

　　Another popular surface treatment is electroless nickel immersion gold (ENIG). It involves depositing a layer of nickel on the copper surface followed by a thin layer of gold. ENIG offers excellent corrosion resistance and good electrical conductivity. It is suitable for high-reliability applications and fine-pitch components as it provides a very flat and uniform surface. However, it is more expensive than HASL and can have issues with gold embrittlement if not properly controlled.

　　Organic solderability preservatives (OSPs) are also commonly used. OSPs form a thin organic layer on the copper surface that protects it from oxidation and maintains solderability. They are cost-effective and environmentally friendly. However, the OSP layer is relatively thin and may be damaged during handling or storage, requiring careful handling and short shelf lives.

　　The choice of PCB surface treatment depends on various factors such as the application requirements, cost considerations, and the type of components to be used. Different surface treatments can affect the solderability, reliability, and long-term performance of the PCB. Therefore, careful evaluation and selection of the appropriate surface treatment are essential in the PCB manufacturing process.