1. Chemical nickel gold is also known as chemical immersion gold or immersion gold. Typically, the thickness of the electroless nickel layer used on the copper metal surface of the PCB is 2.5um-5.0um, and the thickness of the immersion gold (99.9% pure gold) layer is 0.05um-0.1um (formerly PCB). Replace the gold coins in the pcb pool. Technical advantages: smooth surface, long storage time, easy to solder; suitable for fine pitch components and thinner PCB. For FPC, it is more suitable because it is thinner. Disadvantages: not environmentally friendly.
2, tin-lead plating advantages: can directly add flat lead tin on the pad, with good solderability and uniformity. For some processes (such as HOTBAR), this method must be used on the FPC. Disadvantages: Lead is easy to oxidize, storage time is short; need to pull plating line; not environmentally friendly.
3. Selective Electroplating Gold (SEG) Selective plating gold means that part of the PCB is plated with gold, while other areas are treated with another surface treatment. Electroplating gold refers to the application of a nickel layer on the copper surface of the PCB and then electroplating the gold layer. The thickness of the nickel layer is from 2.5 μm to 5.0 μm, and the thickness of the gold layer is usually from 0.05 μm to 0.1 μm. Advantages: The gold plating layer is thick and has strong oxidation resistance and wear resistance. “Golden Finger” generally uses this treatment. Disadvantages: not environmentally friendly, cyanide pollution.
4. Organic Solderability Protective Layer (OSP) This process refers to the surface coating of the bare PCB copper surface with specific organic matter. Advantages: Provides a very flat PCB surface to meet environmental requirements. Suitable for PCBs with fine pitch components.
Disadvantages: PCBA with traditional wave soldering and selective wave soldering processes is required, and OSP surface treatment is not allowed.
5. Hot Air Leveling (HASL) This process refers to 63/37 lead-tin alloy covering the bare metal surface of the PCB. The hot air leveling lead-tin alloy coating has a thickness of 1 um to 25 um. The hot air leveling process makes it difficult to control the thickness of the plating and the land pattern. Not recommended for PCBs with fine pitch components because fine pitch components require high flatness of the pads; hot air leveling is suitable for thin FPCs.
In design, FPC often needs to be used with PCBs. Among the connections between the two, board-to-board connectors, connectors and gold fingers, HOTBAR, soft and hard bond plates, and manual soldering are often used for different applications. On the environmental side, designers can use the appropriate connection method.
In practical applications, it is determined according to the application requirements whether ESD shielding is required. When FPC flexibility is not high, it can be achieved with solid copper and thick media. When flexibility is required.