Common methods for protecting FPC

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 2.5 um - 5.0 um, and the thickness of the immersion gold (99. 9% pure gold) layer is 0.05 um - 0.1 um (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. The advantages of tin-lead plating: can be directly added to the pad on the lead, tin, 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 of gold means that part of the PCB is gold plated while other areas are treated with another surface. 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 Fingers" usually use 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 substances. 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 is a 63/37 lead-tin alloy that covers the bare metal surface of the PCB. The hot air leveling lead-tin alloy coating has a thickness of from 1 micron to 25 microns. The hot air leveling process makes it difficult to control the thickness and land pattern of the plating. It is not recommended for PCBs with fine pitch components because fine pitch components require high flatness of the pads; hot air flattening is suitable for thin FPCs.