Do you know the principle of gold and gold plating on PCB?

Anti-oxidation, spray tin, lead-free spray tin, immersion gold, immersion tin, immersion silver, hard gold plating, full plate gold plating, gold finger, nickel palladium gold OSP: lower cost, good solderability, storage conditions, time Short, environmentally friendly, well welded and flat.

Spray tin: The tin-coated board is generally a multi-layer (4-46 layer) high-precision PCB model. It has been used by many large domestic communications, computers, medical equipment and aerospace companies and research units. ) is the connection between the memory module and the memory slot, all signals are transmitted through the gold finger.

The gold finger is composed of a plurality of golden conductive contacts. Because the surface is gold-plated and the conductive contacts are arranged like a finger, it is called a "golden finger". The gold finger is actually coated with a layer of gold on a copper clad plate by a special process because gold is highly resistant to oxidation and has high conductivity. However, because of the high price of gold, more memory is currently replaced by tin plating. Since the 1990s, tin materials have become popular. At present, the "golden fingers" of motherboards, memory and graphics cards are almost always used. Tin material, only some of the high-performance server / workstation accessories contact points will continue to use gold-plated practices, the price is naturally high.

Second, why use gold plate

As ICs become more integrated, the IC pins are more dense. The vertical tin-spraying process is difficult to flatten the fine pads, which makes the placement of the SMT difficult; in addition, the shelf life of the tin-plate is very short. The gold plate just solves these problems:

1. For surface mount technology, 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 reflow soldering. Therefore, the whole board Gold plating is common in high density and ultra small surface mount processes.

2, in the trial production stage, affected by factors such as component procurement, often the board is not immediately welded, but often has to wait for a few weeks or even a month to use, the shelf life of the gold-plated board (shelf life) than lead Tin alloys are many times longer, so everyone is willing to adopt them. In addition, the cost of gold-plated PCBs in the sample phase is comparable to that of lead-tin alloy plates. But as the wiring becomes denser, the line width and spacing have reached 3-4 MIL. Therefore, the problem of short circuit of gold wire is brought about: As the frequency of the signal is higher and higher, the effect of the signal transmission in the multi-plating layer on the signal quality is more obvious due to the skin effect. The skin effect refers to: high frequency alternating current, the current will tend to concentrate on the surface of the wire. According to the calculation, the skin depth is related to the frequency.

Third, why use Shenjin board

In order to solve the above problems of gold-plated plates, the PCBs using the immersion gold plate mainly have the following characteristics:
1. Because the crystal structure formed by immersion gold and gold plating is different, Shenjin will be golden yellow and more yellow than gold plating, and 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, which will not cause poor soldering and cause customer complaints.
3. Because the gold plate only has nickel gold on the pad, the signal transmission in the skin effect is not affected by the signal in the copper layer.
4. Because of the gold plating, the crystal structure is denser and it is not easy to produce oxidation.
5, because the gold plate only has nickel gold on the pad, so it will not produce gold wire and cause it to be short.
6. Because the gold plate has only nickel gold on the pad, the solder joint on the line is more firmly bonded to the copper layer.
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 the immersion gold plate is easier to control, and it is more conducive to the processing of bonding for the products with bonding. At the same time, because Shenjin is softer than gold plating, the gold plate is not wearable. 9. The flatness and standby life of the Shenjin board are as good as the gold plate. Fourth, the gold plate VS gold plate is actually divided into two kinds of gold plating process: one is electroplating gold, one is immersion gold.

For the gold plating process, the effect of the tin on it is greatly reduced, and the effect of the gold on the gold is better; unless the manufacturer requires the binding, otherwise most manufacturers will choose the gold process! In the case of PCB surface treatment is the following: gold plating (gold plating, immersion gold), silver plating, OSP, spray tin (lead and lead-free), these are mainly for FR-4 or CEM-3 and other plates In other words, the paper base material also has a surface treatment method of applying rosin; the bad tinning (poor tin eating) is excluded from the production and material processing reasons of the solder paste and the like.

Here only for PCB problems, there are several reasons: 1, in the PCB printing, whether there is oil film on the PAN position, it can block the effect of tin; this can be done by the soldering test.
2. Whether the PAN bit is in compliance with the design requirements, that is, whether the pad design is sufficient to ensure the support of the part.
3. Whether the pad is contaminated, this can be obtained by ion contamination test; the above three points are basically the key aspects considered by PCB manufacturers. The advantages and disadvantages of several methods of surface treatment are that each has its own strengths and weaknesses! In terms of gold plating, it can make the PCB storage for a long time, and it is less affected by the external environment temperature and humidity (relative to other surface treatments), generally can be stored for about one year; the tin surface treatment is second, OSP again, this Both surface treatments should pay attention to a lot of storage time in ambient temperature and humidity. Under normal circumstances, the surface treatment of immersion silver is a bit different, the price is high, the storage conditions are more demanding, and it needs to be processed with sulfur-free paper packaging! The storage time is about three months! In terms of tin effect , Shen Jin, OSP, Spray tin is actually almost the same, manufacturers mainly consider the cost performance!