connecting finger( gold finger ) boards need gold plating or immersion gold
I. Immersion Gold VS Gold Plating
Immersion gold adopts the method of chemical deposition. A layer of coating is formed by a chemical redox reaction. Generally, the thickness is thicker.
Gold plating uses the principle of electrolysis, also known as electroplating. Most other metal surface treatments are also electroplated.
In actual product applications, 90% of gold plates are immersion gold boards, because the poor weldability of gold-plated boards is a fatal shortcoming, and it is also the direct reason why many companies give up the gold-plating process!
The immersion gold process deposits a nickel-gold coating with stable color, good brightness, smooth coating, and good solderability on the surface of the printed circuit. Basically, it can be divided into four stages: pre-treatment (oil removal, micro-etching, activation, post-dipping), nickel immersion, gold immersion, and post-treatment (waste gold washing, DI washing, drying). The thickness of immersion gold is between 0.025-0.1um.
Gold is used in the surface treatment of circuit boards, because gold has strong conductivity, good oxidation resistance, and long life, and is generally used in keyboards, gold fingerboards, etc. The most fundamental difference between gold-plated boards and immersion gold boards is that gold-plated is hard Gold (wear-resistant), and immersion gold is soft gold (not wear-resistant).
II. Different Crystal Structures
The crystal structure formed by immersion gold and gold plating is different.
The thickness of immersion gold is much thicker than that of gold plating. Immersion gold will be golden yellow, which is more yellow than gold plating (this is one of the methods to distinguish between gold plating and immersion gold). a), the gold-plated ones will be slightly whitish (the color of nickel).
Compared with gold plating, immersion gold is easier to solder and will not cause poor welding. The stress of the immersion gold board is easier to control, and for products with bonding, it is more conducive to the processing of bonding. At the same time, it is precise because immersion gold is softer than gold plating, so the gold finger of the immersion gold board is not wear-resistant (the disadvantage of immersion gold board).
III. The Advantages of Immersion Gold Circuit Board
The immersion gold board only has nickel-gold on the pad. The transmission of the signal in the skin effect is in the copper layer and will not affect the signal.
Compared with gold plating, immersion gold has a denser crystal structure and is not easy to produce oxidation.
With the increasing requirements of circuit board processing accuracy, the line width and spacing have reached below 0.1mm. Gold plating is prone to short circuits of gold wire. The immersion gold board only has nickel gold on the pad, so it is not easy to produce a short circuit of gold wire.
The immersion gold board only has nickel-gold on the pad, so the combination of the solder mask on the circuit and the copper layer is stronger. The project will not affect the spacing when compensating.
For boards with higher requirements, the flatness requirements are better, immersion gold is generally used, and the black pad phenomenon after assembly is generally not caused by immersion gold. The flatness and service life of the immersion gold boards are better than that of the gold-plated ones.
Therefore, most factories currently use the immersion gold process to produce PCB with gold. 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-priced products that use the gold plating process (such as remote control boards, and toy boards).