Electroless Ni-Pd-Au plating is an important surface treatment process in the printed circuit board industry, which is widely used in the production processes of hard circuit boards (PCB), flexible printed circuit board (FPC), rigid bonding boards and metal substrates, and is also an important development trend of surface treatment in the printed circuit board industry in the future. 1. Types of surface treatment of printed circuit boards. Printed circuit board is the foundation of all electronic products, involving communication, lighting, aviation, aerospace, transportation, home appliances, military, medical equipment and other fields, so the development of printed circuit board industry is related to the development speed of the whole electronic industry. Surface treatment is the most important part in the manufacturing process of printed circuit boards. At present, there are eight mature surface treatment processes in the market, including tin spraying (hot air leveling process), tin precipitation, silver precipitation, OSP (organic protective film), hard gold/water gold plating, nickel gold plating, electroless nickel gold plating and electroless nickel palladium gold plating. Each process has certain advantages and disadvantages in use, processing difficulty and cost control.