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PCB Tech

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PCB Tech

PCB Tech

PCB circuit board surface treatment process-the difference between gold-immersed board and gold-plated board
2021-09-13
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Author:Frank

There are several treatment processes for the surface of the circuit board: bare board (no treatment on the surface), rosin board, OSP (organic solder protectant, slightly better than rosin), tin spraying (lead tin, lead-free tin), gold-plated board, Shen Jinban, etc., these are relatively perceptible.
[PCB Information Network] There are several treatment processes for the surface of the circuit board: bare board (no treatment on the surface), rosin board, OSP (organic solder preservative, slightly better than rosin), tin spraying (lead tin, lead-free tin) ), gold-plated board, immersion gold board, etc., these are more perceptible.

We briefly introduce the difference between gold plating and immersion gold process.

Gold finger boards need to be gold-plated or immersed gold
The difference between immersion gold process and gold plating process

Immersion gold adopts a chemical deposition method, which generates a layer of plating through a chemical oxidation-reduction reaction method, which is generally thicker. It is a kind of chemical nickel-gold layer deposition method, which can reach a thicker gold layer.

pcb board

Gold plating uses the principle of electrolysis, also called electroplating. The surface treatment of other metals is mostly electroplating.
In actual product applications, 90% of the gold plate is immersion gold plate, because the poor weldability of the gold plate is his fatal shortcoming, and it is also the direct reason why many companies abandon the gold plating process!
Immersion gold process deposits a nickel-gold coating with stable color, good brightness, flat coating and good solderability on the surface of the printed circuit. Basically, it can be divided into four stages: pre-treatment (degreasing, micro-etching, activation, post-dipping), immersion of nickel, immersion of gold, and post-treatment (washing waste gold, washing with DI water, and 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, it is generally used in key boards, gold finger boards, etc. However, the most fundamental difference between gold-plated boards and immersed gold boards is that gold-plated boards are hard Gold (wear-resistant), Immersion Gold is soft gold (not wear-resistant).
1. Immersion gold is different from the crystal structure formed by gold plating. Immersion gold is much thicker than gold plating. Immersion gold will be golden yellow, which is more yellow than gold plating (this is one of the ways to distinguish between gold plating and immersion gold. A), the gold-plated will be slightly whitish (nickel color).
2. Immersion gold and gold plating have different crystal structures. Immersion gold is easier to weld than gold plating and will not cause poor welding. The stress of the immersion gold plate is easier to control, and for products with bonding, it is more conducive to the processing of bonding. At the same time, it is precisely because the immersion gold is softer than the gilding, so the immersion gold plate is not wear-resistant as the gold finger (the disadvantage of the immersion gold plate).
3. The immersion gold board only has nickel and gold on the pads, and the signal transmission in the skin effect is on the copper layer without affecting the signal.
4. Immersion gold has a denser crystal structure than gold plating, and it is not easy to produce oxidation.
5. As the precision requirements for circuit board processing are getting higher and higher, the line width and spacing have been below 0.1mm. Gold plating is prone to pcb short circuit of gold wire. The immersion gold board only has nickel gold on the pad, so it is not easy to produce gold wire short circuit.
6. The immersion gold board only has nickel and gold on the pads, so the solder mask on the circuit and the copper layer are more firmly combined. The project will not affect the spacing during compensation.
7. For high-demand boards, the flatness requirements are better. Generally, immersion gold is used, and immersion gold generally does not appear as a black pad after assembly. Immersion gold plate has better flatness and service life than gold plate.
Therefore, most factories currently use the immersion gold process to produce gold plates. However, the immersion gold process is more expensive (higher gold content) than the gold plating process, so there are still a large number of low-priced products that use the gold plating process (such as remote control boards, toy boards).