The difference between electroless gold plating and electroplating gold (electroless gold plating is also called immersion gold; gold plating usually refers to electroplating gold).
1.The difference in principle
FLASH GOLD (electroless gold plating) uses the method of chemical deposition!
PLANTING GOLD uses the principle of electrolysis!
2.The difference in appearance
Electroplating gold has electro-gold leads, while electroless gold does not. And if the thickness of the gold plating film is not high, the method of electroless gold plating is used.
For example, the memory module PCB uses electroless gold plating on its PAD surface.
And TAB (Gold Finger) uses electroplated gold and electroless gold!
3.The difference in production process
Electroplating gold, like other electroplating, needs to be energized and requires a rectifier. There are many kinds of processes, including cyanide-containing, non-cyanide systems, non-cyanide systems and citric acid type, sulfite type, etc. All used in the PCB industry are non-cyanide systems.
Electroless gold plating does not require electricity, it deposits gold on the surface of the board through a chemical reaction in the solution. They have their own advantages and disadvantages, except for electricity and no electricity, electroplating gold can be made very thick, as long as the time is extended, it is suitable for making a state A certain board. The chance of abandoning electroplated gold potion is smaller than that of electroless gold plating. However, electroplating gold requires full board conduction, and it is not suitable for very thin circuits. Electroless gold plating is generally very thin (less than 0.2 microns), the purity of gold is low, and the working fluid can only be discarded when it is used to a certain extent.
The main features of electroplated gold circuit boards are as follows:
- The wettability of the electro-gold board and OSP is equivalent, and the wettability of the immersion tin board of the gold-plated board is the best of all PCB finishing.
- The thickness of electric gold is much greater than that of chemical gold, but the flatness is not as good as that of chemical gold.
- Electro-gold is mainly used for gold fingers (wear-resistant), and there are many pads.
Electroless gold-plated circuit boards mainly have the following characteristics:
- Immersion gold board will be golden yellow, customers are more satisfied.
- Immersion gold plates are easier to weld and will not cause customer complaints due to poor welding.
- 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 quality.
Why use electroplated gold plate
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 electroplated gold plate just solves these problems:
- 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 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.
- 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 often has to wait several weeks or even months before using it. The shelf life of the gold-plated board is better than that of lead. Tin alloy is many times longer, so everyone is happy to use it. Besides, the cost of gold-plated PCB in the sample stage is almost the same as that of lead-tin alloy board.
However, as the wiring becomes denser, the line width and spacing have reached 3-4MIL, which brings about the problem of short circuit of the 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 will affect the signal quality more obviously;
The skin effect refers to: high frequency alternating current, the current will tend to concentrate on the surface of the wire to flow.
Why use electroless gold plating
In order to solve the above problems of electroplated gold boards, PCBs using chemical gold boards mainly have the following characteristics:
- 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.
- 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.
- 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 quality.
- Because immersion gold has a denser crystal structure than gold plating, it is not easy to produce oxidation.
- Because the immersion gold board only has nickel and gold on the pads, it will not produce gold wires and cause slight shortness.
- 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.
- The project will not affect the distance during compensation.
- 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 gold plating, so the immersion gold plate is not wear-resistant as the gold finger.
- The flatness and stand-by life of the immersion gold board are as good as the gold-plated board.
Analysis of the advantages and disadvantages of electroless gold plating, electroplating gold, and immersion gold plating
The three are different. Electroless gold plating is a method of chemical oxidation-reduction reaction to generate a layer of plating, which is generally thicker. It is one of the electroless nickel-gold layer deposition methods that can achieve a thicker gold layer; the other is replacement gold , That is, immersion gold, that is, replacement gold, generally thinner, 1-4 micro-inch gold plating generally only electroplated gold, thicker can be plated; chemical gold and immersion gold half are used for relatively high-demand boards, flat The degree of gold plating is better than immersion gold. Generally, gold plating does not show the phenomenon of black pads after assembly; gold plating has higher solder joint strength than the above two because of the higher purity of the plating layer.
