PCB News - The difference between gold-plated circuit boards and gold-plated circuit boards

In electronic products, gold is widely used in contact because of its excellent conductivity, such as key boards, gold finger boards, etc. The most fundamental difference between gold-plated boards and immersed gold boards is that gold-plated is hard gold, and immersed gold is soft gold. . Why do we need two different processes to make circuit boards? Let's analyze the electrical performance below.

1. The difference between immersion gold plate and gold-plated plate: Immersion gold is produced by chemical deposition, and gold-plated is produced by electroplating and ionization.

2. What is a gold-plated circuit board? Why use gold-plated circuit boards?

During the production of gold-plated circuit boards, the entire board will be gold-plated, not only the pads, but also the lines and copper-laying positions will be covered by gold. Gold plating generally refers to electroplating gold, also called electroplated nickel gold plate, electrolytic gold, electro-gold, electro-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 an electric current to form a nickel-gold plating layer on the copper foil surface., Wear-resistant, not easy to oxidize characteristics are widely used in the name of electronic products.

As the integration level of IC becomes higher and higher, IC pins become more 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 ultra-small surface mounts of 0201 and below, because the flatness of the pad is directly related to the quality of the solder paste printing process, it has a decisive influence on the quality of the subsequent reflow soldering, so the whole board Gold plating is common in high-density and ultra-small surface mount processes.

2. In the trial production stage, due to factors such as component procurement, it is often not that the PCB board production is completed and the SMT placement process can be carried out immediately. Sometimes it takes several weeks or even months to start to arrange the SMT placement and the gold-plated board. The shelf life is many times longer than that of pewter, so everyone is willing to use it. Besides, the cost of the gold-plated PCB in the sample stage is almost the same as that of the lead-tin alloy board. But as the wiring becomes denser, the line width and spacing have reached 3-4MIL. Therefore, the problem of gold wire short circuit is brought about. As the frequency of the signal becomes higher and higher, the signal transmission in the multi-plated layer caused by the skin effect has more obvious influence on the signal quality. (Skin effect refers to: high-frequency alternating current, the current will tend to concentrate on the surface of the wire. According to calculations, the skin depth is related to the frequency.)

3. What is an immersion gold circuit board? Why use immersion gold circuit board?

In order to solve the above problems of gold-plated boards, circuit board production engineers have developed a gold-immersion process. Immersion gold is a method of chemical oxidation-reduction reaction to generate a layer of coating. Generally, the deposition thickness of this process is thicker, which is a kind of chemical nickel-gold layer deposition method, which can reach a thicker gold layer, usually called Shen gold.

PCBs using immersion gold technology 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 will not affect the signal on the copper layer.

4. Because the crystal structure of immersion gold is denser than that of 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 distance during compensation.

8. Because the crystal structure formed by gold-immersion and gold-plating is different, the stress of the gold-immersion plate is easier to control, and 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 board are as good as the gold-plated board.

The above is an introduction to the difference between gold-plated circuit boards and gold-plated circuit boards. Ipcb also provides PCB manufacturing and PCB manufacturing methods.