Why “gold plating and immersion gold” on PCB board

782 Published by FASTPCBA 7月 26,2018

Why “gold plating and immersion gold” on PCB board

PCB surface treatment
Anti-oxidation, tin spraying, lead-free tin spraying, gold sinking, tin sinking, silver sinking, hard gold plating, all plate gold plating, gold finger, nickel palladium gold OSP: low cost, good solderability, strict storage conditions, short time, environmental protection technology, good welding, leveling.
Tin spraying: the tin spraying plate is usually a multi-layer (4-46 floors) high-precision PCB model, which has been used by many large communication, computer, medical equipment, aerospace enterprises and research units in China. The connecting finger is the connecting part between the memory slot and the memory slot on the memory stick.
Gold finger: it is made up of a number of golden yellow conductive contacts. It is called “gold finger” because its surface is gold-plated and the conductive contacts are arranged like fingers.The gold finger is actually coated with gold through a special process on the copper clad plate, because the gold is highly resistant to oxidation and has a strong conductivity.Because the price of gold is expensive, however, the current tin plating is used to replace the more memory, tin material from the last century 90 s began to spread, the motherboard, memory, and video devices such as “golden finger” is almost always used tin material, only some high-performance server/workstation accessories will contact point to continue the practice of using gold plated, the price expensive.

Why gold plate
As the integration degree of IC becomes higher and higher, the more and more IC feet become more and more dense.The vertical tin spraying process is difficult to smooth the thin welding disc, which brings difficulty to SMT mounting.In addition, the shelf life of tin spraying plate is very short.The gilt plate is a good solution to these problems:
1. For the surface mounting process, especially for the 0603 and 0402 ultra-small scale sheet mounting process, because the flatness of the welding disc is directly related to the quality of the paste printing process, and plays a decisive role in the later reflow welding quality. Therefore, gold plating on the whole plate is often seen in the high-density and ultra-small scale sheet mounting process.
2, in the development phase, the influence of factors such as components procurement is often not the board to the welding immediately, but often have to wait a few weeks or even months before use, inactive life of gold plated board (shelf life) is longer than the lead tin alloy many times so everyone is willing to adopt. Besides, gold-plated PCB in degrees of the cost of the sample stage compared with pewter plates.
But as the wiring gets tighter, the width and spacing of the wires have reached 3-4mil.
Therefore, the problem of wire short circuit is brought: as the signal frequency is higher and higher, the skin effect causes the signal transmission in the multi-coating layer.According to calculations, skin depth is related to frequency.The more significant the effect on signal quality is.

Gold plating

Why should use sunken gold board
In order to solve the above problems of gold-plated plate, the PCB using gold-plated plate mainly has the following characteristics:
1. As the crystal structure formed by sinking gold is different from that formed by gilding, sinking gold will be golden yellow, which is more yellow than gilding, and the customer will be more satisfied.
2. As the crystal structure formed by sinking gold is different from that formed by gilding, sinking gold is easier to be welded than gilding, which will not cause bad welding and cause customer complaints.
3. Since only the welded plate has nickel gold on it, the signal transmission in the skin effect will not affect the signal in the copper layer.
4. Compared with gold plating, the crystal structure is more dense, and it is not easy to produce oxidation.
5. As the sinking gold plate only has nickel gold on the welding plate, it will not produce gold wire, causing minor short.
6. Since only the welded plate has nickel gold on it, the resistance welding on the wire is more firmly combined with the copper layer.
7. The project will not affect the spacing when making compensation.
8. Due to the different crystal structure formed by sinking gold and gold plating, the stress of its sinking gold plate is easier to control, which is more conducive to the processing of boding products.At the same time because sinking gold is softer than gold plating, so sinking gold plate does not wear gold fingers.
9. The leveling property of the gold plate is as good as that of the gold plate.

Gold plating VS immersion gold(Gold plating and immersion gold)
In fact, there are two kinds of gold plating process: one is electric gold plating and the other is heavy gold.
For the gilding process, the effect of tin on it is greatly reduced, while the effect of tin on heavy gold is better.Unless what the manufacturer asks is to bind, otherwise now most manufacturer will choose sink gold craft!Generally, the surface treatment of PCB is as follows: gold plating (electroplating, gold sinking), silver plating, OSP, tin spraying (lead and lead-free). These are mainly used for fr-4 or cem-3, paper substrate and rosin coating.Bad tinning (bad tin eating) if the tin paste manufacturers such as tin paste excluded from the production and material technology.
Here, only for the PCB problem, there are the following reasons:
1. In PCB printing, is there any oil permeable film surface on PAN, which can block the tin effect;This can be verified by floating tin test.
2. Whether the fountain position of PAN position meets the design requirements, that is, whether the welding disc design can ensure enough support of parts.
3. Whether the welding plate is contaminated, which can be obtained by ion contamination test;The above three points are mainly considered by PCB manufacturers.
As for the advantages and disadvantages of surface treatment, each has its own advantages and disadvantages!
In terms of gilding, it can keep PCB for a long time, and it is subject to small changes in temperature and humidity (compared with other surface treatments) in the external environment. Generally, it can be stored for about a year.Spray tin surface treatment second, OSP again, these two surface treatment in the environment temperature and humidity storage time to pay attention to a lot.
In general, the surface treatment of sinking silver is a little different, the price is also high, the storage conditions are more stringent, need to be treated with non-sulfur paper packaging!And save in about three months!In the tin effect aspect, sink gold, OSP, spray tin and so on are actually similar, manufacturers are mainly concerned about cost performance!

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