The difference between immersion gold process and gold plating process of display PCB
Gold-plated PCB: golden and white, poor welding, skin effect is not conducive to high-frequency signal transmission,Disadvantages: The gold surface is easy to oxidize, which is easy to cause the gold wire to be short, and the welding bonding strength is not strong.
Immersion gold PCB: golden yellow, good weldability, skin effect has no effect on the signal.Advantages: It is not easy to oxidize, no gold wire is produced, and the welding resistance is good.
Immersion gold uses a chemical deposition method, which generates a layer of plating through a chemical oxidation-reduction reaction, which is generally thicker. It is a kind of chemical nickel gold gold layer deposition method and can reach a thicker gold layer.
Gold plating uses the principle of electrolysis, also called electroplating. Most other metal surface treatments also use electroplating.In actual product applications, 90% of the gold plates are immersion gold plates, because poor weldability of gold-plated plates is his fatal shortcoming, and it is also a direct reason for many companies to abandon the gold-plating process!
The immersion gold process deposits a nickel-gold coating with stable color, good brightness, smooth plating, and good solderability on the surface of the printed circuit. Basically can be divided into four stages: pre-treatment (degreasing, micro-etching, activation, post-immersion), nickel precipitation, gold precipitation, post-treatment (washing of waste gold, DI washing, drying). Immersion gold thickness is between 0.025-0.1um.
The display PCB is applied to the surface treatment of the circuit board, because gold has strong conductivity, good oxidation resistance, and long life. It is generally used in key panels, gold finger boards, etc. The fundamental difference between gold plated and immersion gold plate is that gold plated It is hard gold (wear-resistant), and sink gold is soft gold (not wear-resistant).1. The crystal structure formed by immersion gold and gold plating is different. The thickness of immersion gold for gold is much thicker than that of gold plating. Immersion gold will be golden yellow and yellower than gold plating (this is the method to distinguish gold plating from gold plating A), the gold-plated ones will turn slightly white (the color of nickel).
2. The crystal structure formed by immersion gold and gold plating is different. Immersion gold is easier to weld than gold plating, and will not cause poor welding. The stress of the immersion gold board is easier to control, and for the products with bonding, it is more conducive to the processing of bonding. At the same time, it is precisely because the gold sink is softer than the gold-plated, so the gold finger of the gold sink board is not wear-resistant (the disadvantage of the gold sink board).
3. Immersion gold plate only has nickel gold on the pad. The signal transmission in the skin effect is in the copper layer and will not affect the signal.4. Immersion gold has a denser crystal structure than gold plating and is not easy to produce oxidation.
5. With the increasing accuracy requirements of circuit board processing, the line width and spacing have reached below 0.1mm. Gold plating is prone to short circuit of gold wire. Immersion gold plate only has nickel gold on the pad, so it is not easy to produce gold wire short circuit.
6. Immersion gold board only has nickel gold on the pad, so the combination of solder mask and copper layer on the circuit is stronger. The project will not affect the spacing when making compensation.7. For the more demanding boards, the flatness requirements are better. Generally, immersion gold is used, and the immersion gold generally does not appear to be black mat after assembly. The flatness and service life of the immersion gold plate are better than that of the gold plating.
Therefore, at present, most factories have adopted the immersion gold process to produce gold plates. However, the immersion gold process is more expensive than the gold plating process (the gold content is higher), so there are still a large number of low-cost products using gold plating process.
