The difference between Immersion gold and gold plate
Today, I will talk about the difference between Immersion gold and gold plating of the PCB board.Immersion gold and the gold plate are the crafts often used in PCB circuit boards. Many customers cannot correctly distinguish the difference between the two. Some customers even think that the two are not exist differences, this is a very wrong view and must be corrected in time. So what impact do these two “golden plates” have on the board? Below I will explain specifically to you.
First, the difference between the Immersion gold and the gold plate
What is gold plating?
Gold plating on the whole plate: generally refers to [electroplating gold] [electroplated nickel plate], [electrolytic gold], [electric gold], [electric nickel plate], with soft gold and hard gold (usually used as gold finger) . The principle is to dissolve nickel and gold (commonly known as gold salt) in chemical syrup, immersing the circuit board in the plating tank and applying current to form a nickel-gold plating on the copper foil surface of the circuit board, and the electro-nickel gold is coated. The high hardness, wear resistance and non-oxidation characteristics are widely used in electronic products.
What is Immersion gold?
A chemical oxidation-reduction reaction is used to form a coating layer, which is generally thick, and is a kind of chemical nickel gold gold layer deposition method, which can reach a thick gold layer, which is usually called Immersion gold.
Due to the fatal lack of weld ability of gold-plated board, many manufacturers have not produced gold-plated board since 2008. In the actual trial process, 90% of gold plates can be replaced by gold-plated plates, which is also the direct result of abandoning gold-plated boards. In the process of usage, because of the small conductivity of gold, it is widely used in contact circuit, such as key plates, gold finger plates, etc. The most fundamental difference between gold plate and Immersion gold is that gold plate is hard gold, and Immersion gold is soft. The following analysis based on electrical performance !
Second, why use of gold plate
As IC become more integrated, the IC pins are more dense. The vertical tin-spraying process is difficult to flatten the thinned pads, which makes the mounting of the SMT difficult; in addition, the shelf life of the tin-plated board is very short. The gold-plated plate solves these problems: 1 For the surface mount process, especially for the 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, the quality of the reflow soldering behind has a decisive influence. Therefore, the whole plate gold plating is common in high density and ultra small surface mount processes. 2 In the trial production stage, due to the factors such as component procurement, it is often not the board to be welded immediately, but it is often unavoidable to wait for a few weeks or even a month to use, the shelf life of gold-plated plates is many times longer than that of lead-tin alloys, so everyone is happy to adopt them. In addition, the cost of the gold-plated PCB in the sample phase is comparable to that of the lead-tin alloy plate.
But as the wiring gets denser, the line width and spacing have reached 3-4 MIL. Therefore, the problem of short circuit of gold wire is generated:
As the frequency of the signal becomes 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 frequency:
Third, why use Immersion gold board
In order to solve the above problems of gold-plated boards, the PCB using the immersion gold boards mainly have the following characteristics:
1, Because the crystal structure formed by immersion gold and gold plating is different, the immersion gold will be golden yellow and more yellow than gold plating, and the customer is 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 welding and cause customer complaints.
3, Because the gold plate has only 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 plate, the crystal structure is denser and it is not easy to produce oxidation.
5, Because the Immersiongold board only has nickel gold on the pad, so it will not produce gold wire and cause it to be short.
6, Because the Immersiongold board has only nickel gold on the pad, the solder joint on the wire 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 boardis easier to control, and it is more conducive to the processing of bonding for the products with bonding. At the same time, because Immersion gold is softer than gold plating, the Immersion gold is not wearable.
9, The flatness and standby life of the Immersion gold are as good as the gold plate.
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