Why do “ gold plating” on the PCB board


 01  PCB surface finish

Antioxidant, HASL, HASL without lead,Sink tin, Sink silver, Sink gold, Hard gold plating , All board gold-plated ,Gold finger, Sink nickel palladium gold OSP: low cost, good weldability, strict storage conditions, short time, environmental protection technology, good welding and leveling.

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HASL: HASL board  is commonly layers (layer 4-46) with high precision PCB model, has been more than domestic large communication, computer, medical equipment and aerospace companies and research institutes can use gold finger (connecting finger) is memory chips and memory slot connections between components, all of the signals are transmitted through the gold finger.

 

The gold finger is actually a layer of gold on the copper plate, because it has strong antioxidant properties and is highly conductive. Because the price of gold is expensive, however, at present HASL is used to replace Sink gold on the memory, from the last century 90 s tin material began to spread, "golden finger"of the board, memory, and video devices such as is almost always used tin material at the moment, only some parts of the high performance server/workstation will continue to use the gold-plated method, and the price will be very high.

 

02 Why do we need to use the gold-plating board

As IC integration becomes higher and higher, IC pins are more dense. However, the vertical spray tin process can hardly be smooth and smooth, which brings difficulty to SMT's pasting. The shelf life is very short. And the gold-plating board were able to solve these problems:

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For SMT process, especially for 0603 and 0402 subminiature table stick, because the welding plate flatness is directly related to the quality of the solder paste printing process, play a decisive influence on the back of the reflow welding quality, so, all board gold-plating often seen in high density and subminiature table stick process.

 

In the trial production stage, affected by factors such as components purchasing, the boardoften is not welding immediately, but often have to wait a few weeks or even months before welding,the shelf life of gold-plating board is much longer than the lead tin alloy, so everyone is happy to use it. Moreover, the cost of gold-plating PCB in the sample stage is similar to that of lead tin alloy board.

 

But as the wiring becomes more dense, the line width and spacing have reached 3-4mil.

 

Because the problem of the gold wire short circuit: as the frequency of the signal increases, the effect of the skin effect on the signal quality is more obvious when the signal is transmitted in the multilayer plating.

 

The conductor skin effect refers to the high frequency alternating current, which tends to focus on the surface flow of the conductor. According to the calculation, the conductor skin  depth is related to the frequency.

 

03 Why do we need to use Sink gold board

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In order to solve the above problems of gold-plating board, PCB with sink gold has the following characteristics:

1. The crystal structure between the gold plating and sink gold are different, sink gold is more yellow than gold plating, and customers are more satisfied it.

2. Because the sink gold board only has nickel gold on the solder plate, the signal transmission in the conductor skin effect will not affect the signal in the copper layer.

3. Because the sink gold board only has the nickel gold on the plate, so it will not produce the gold wire to cause the microshort.

4. Because the sink gold board only has nickel gold on the solder plate, the resistance welding with the copper layer on the line is stronger.

5. The flatness and shelf life of the sink gold board is as good as the gold plating board.

 

The advantages and disadvantages of several ways of surface technology, they all have their own strengths and weaknesses!

 

On the gold-plating side, it can hold the PCB for longer, and it is less subject to the ambient temperature and humidity (compared with other surface technology), which can be kept for a year or so long. On the surface of the sink tin, the OSP is again, and the two kind of surface technology should be paid much attention to the storage time of environmental temperature and humidity.