PCB Tech - The difference between PCB immersion gold board and gold-plated board

The difference between PCB immersion gold board and gold-plated board

Jiali Chuang has not produced gold-plated plates since 2008. In the actual trial process, 90% of the gold plates can be replaced by immersed gold plates. The poor weldability of the gold-plated plates is his fatal shortcoming, which also caused Jiali Chuang to give up gold plating. The direct cause of the board! In the process of use, gold is widely used in contact circuits, such as key boards, gold finger boards, etc., because of its low conductivity. The most fundamental difference between gold-plated boards and immersed gold boards is that gold-plated is hard gold and immersed gold is soft Jin, let’s analyze the electrical performance below!
1. The difference between immersion gold board and gold-plated board
2. Why use gold-plated plates
With the increasing integration of IC, the more IC pins become denser. The vertical spray tin process is difficult to flatten the thin pads, which brings difficulty to the placement of smt; in addition, the shelf life of the spray tin plate is very short. The gold-plated board just solves these problems: 1 For the surface mount process, especially for 0603 and 0402 ultra-small surface mounts, because the flatness of the pad is directly related to the quality of the solder paste printing process, it is important for the quality of the subsequent reflow soldering. Therefore, the whole board gold plating is common in the high-density and ultra-small surface mount process. 2 In the trial production stage, due to factors such as component procurement, it is often not that the board is soldered as soon as it comes, but it is often used for several weeks or even months. The shelf life of the gold-plated board is better than that of lead-tin combine
Gold is many times longer, so everyone is willing to adopt it. Besides, the cost of gold-plated PCB in the sample stage is almost the same as that of lead-tin alloy board.
But with the denser wiring, the line width and spacing have reached 3-4MIL. This brings about the problem of short circuit of gold wire:
As the frequency of the signal becomes higher and higher, the signal transmission in the multi-plated layer caused by the skin effect has a more obvious impact on the signal quality
Skin effect refers to: high frequency alternating current, the current will tend to concentrate on the surface of the wire to flow.
According to calculations, skin depth is related to frequency

The other shortcomings of gold-plated board have been listed in the table of difference between immersion gold board and gold-plated board.
Three, why use heavy gold plate;
In order to solve the above problems of gold-plated boards, PCBs using immersion gold boards mainly have the following characteristics:
1. Because the crystal structure formed by immersion gold and gold plating is different, immersion gold will be golden yellower than gold plating, and customers will be more satisfied.
2. Because 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 and cause customer complaints.
3. Because the immersion gold board only has nickel and gold on the pad, the signal transmission in the skin effect is on the copper layer and will not affect the signal.
4. Because immersion gold has a denser crystal structure than gold plating, it is not easy to produce oxidation.
5. Because the immersion gold board only has nickel and gold on the pads, it will not produce gold wires and cause slight shortness.
6. Because the immersion gold board only has nickel and gold on the pads, the solder mask on the circuit and the copper layer are more firmly bonded.
7. The project will not affect the spacing during compensation.
8. Because the crystal structure formed by immersion gold and gold plating is different, the stress of the immersion gold plate is easier to control. For products with bonding, it is more conducive to bonding processing. 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.
9. The flatness and stand-by life of the immersion gold plate is as good as that of the gold plate.
1. What is gold plating: the whole board is gold-plated. Generally refers to [electroplating gold] [electroplating nickel gold plate], [electrolytic gold], [electric gold], [electric nickel gold plate], there is a distinction between soft gold and hard gold (usually used as gold fingers). The principle is to dissolve nickel and gold (commonly known as gold salt) in chemical water, immerse the circuit board in the electroplating cylinder and pass current to form a nickel-gold plating layer on the copper foil surface of the circuit board. The characteristics of high hardness, wear resistance, and resistance to oxidation are widely used in electronic product names.