I. The difference between immersion gold and gold plating
1. Principle differenceIMMERSION GOLD uses a chemical deposition method.
PLANTING GOLD uses the principle of electrolysis.
2. The difference in appearanceElectric gold will have electric gold leads, while chemical gold will not. And if the gold thickness is not high, it is the method of melting gold. For example, the memory stick PCB, its PAD surface uses a gold method. The TAB (gold finger) uses both electric gold and chemical gold.
3. Difference in production processGold plating, like other electroplating, requires electricity and requires a rectifier. It has a variety of processes, including cyanide, non-cyanide system, non-cyanide system and citric acid type, sulfite type, etc. Used in the PCB industry All are non-cyanide systems.
Chemical gold (electroless gold plating) does not require electricity, it is deposited on the surface of the board through the chemical reaction in the solution. They have their own advantages and disadvantages. In addition to being powered and not powered, electric gold can be very thick, as long as the time is extended. It is suitable for bonding boards. The chance of discarding electric gold syrup is less than that of gold. However, electricity gold requires full board conduction, and it is not suitable for making particularly thin circuits. Gold is generally very thin (less than 0.2 microns), The purity of gold is low. To a certain extent, the working fluid can only be discarded.
The circuit board of electric gold board mainly has the following characteristics:1. The wettability of the electric gold plate is equivalent to that of the OSP, and the wettability of the gold-immersed tin plate is the best of all PCB finishing.
2. The thickness of the electrical gold is much greater than the thickness of the gold, but the flatness is not as good as the gold.
3. Electric gold is mainly used for gold fingers (wear-resistant), and there are many pads.
The circuit board of Shenjin board mainly has the following characteristics:1. The Shenjin board will be golden yellow, and customers are more satisfied.
2. Immersion gold plate is easier to weld, and will not cause poor welding to cause customer complaints.
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 quality.
II. Why use gold plating?As the integration of ICs becomes higher and higher, the IC pins are more and more dense. The vertical soldering process is difficult to flatten the thin pads, which brings difficulty to SMT placement; in addition, the shelf life of the soldering board is very short. The gold-plated plate just solved these problems:
1. For the surface mount technology, especially for 0603 and 0402 ultra-small surface mount, 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, the influence of factors such as component procurement is often not soldered immediately after the board comes, but often has to wait for a few weeks or even a month before use. The shelf life of gold-plated plates is higher than that of lead Tin alloys are many times longer, so everyone is happy to adopt them. Besides, the cost of gold-plated PCB in the sample preparation stage is almost the same as that of lead-tin alloy board.
But as the wiring becomes denser and denser, the line width and spacing have reached 3-4MIL, so it brings about the problem of short circuit of the gold wire;As the frequency of the signal becomes higher and higher, the effect of the signal transmission in the multi-coating layer due to the skin effect has a more obvious impact on the signal quality;
Skin effect refers to: high-frequency alternating current, current will tend to concentrate on the surface of the wire flow.
III. Why use Immersion Gold?
In order to solve the above problems of the gold-plated board, the PCB using the gold plate has the following characteristics:1. Because the crystal structure formed by immersion gold and gold plating is different, immersion gold will be golden yellow than gold plating, and the customers are 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 only gold on the pad of the Immersed Gold board, the signal transmission in the skin effect is in the copper layer and will not affect the signal quality.
4. The crystal structure of immersion gold is more dense than gold plating, and it is not easy to produce oxidation.
5. Because the gold plate only has nickel gold on the pad, it will not produce gold wire and cause shortness.
6. Because the gold plate only has nickel gold on the pad, the combination of the solder mask on the circuit and the copper layer is stronger.
7. The project will not affect the spacing when making compensation.
8. Because the crystal structure formed by immersion gold and gold plating is different, the stress of its immersion gold plate is easier to control, and for the 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 gold plating, so the immersion gold plate is not wear-resistant.
9. The flatness and service life of the immersion gold plate are as good as the gold-plated plate.