Surface treatment is one of the most important steps in the PCB production process. At present, the common surface treatment methods on the market include tin spraying, immersion tin, immersion gold, bare copper, OSP, etc. Different surface treatment methods have different advantages and disadvantages. For some users who have stricter requirements on circuit boards, the common surface treatment cannot meet the solder mask requirements, and the nickel-palladium-gold process just solves this problem.
Nickel-palladium-gold is a non-selective surface processing technology and the latest surface treatment technology. Its principle is to plate a layer of nickel, palladium and gold on the surface of the copper layer of the PCB. The main process includes: Oil—microetching—presoaking—activation—nickel immersion—palladium immersion—gold immersion—drying, and multi-stage water washing between each link.
The most basic purpose of surface treatment is to ensure good solderability or electrical properties. Since copper in nature tends to exist in the form of oxides in the air, it is impossible to maintain it as raw copper for a long time, so other treatments are required for copper, and common processes such as immersion gold and spray tin have been born.
Compared with other surface treatment methods, nickel-palladium-gold has the advantages of stable durability, excellent solder resistance, good compatibility, high coating flatness, and suitable for high-density pads, so it can be applied to more precise PCBs. The welding performance is also better.
At present, the immersion gold process is widely used. The principle is to wrap a thick layer of nickel-gold alloy with good electrical properties on the copper surface to protect the circuit board for a long time. Compared with immersion gold, nickel-palladium-gold needs to add a layer of palladium between nickel and gold. Palladium can prevent corrosion caused by displacement reaction and fully prepare for immersion gold. Gold can be tightly covered on palladium, providing a good contact surface.
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