First, why use gold plate
With the increasing integration of ICs, the more IC pins are denser. The vertical spray process is difficult to flatten the fine lands, which makes it difficult to mount the SMT. In addition, the shelf life of the spray tin plate is very short. The gold-plated board just solves these problems: 1 For the surface mount process, especially for 0603 and 0402 ultra-small surface mount, because the flatness of the solder pad is directly related to the quality of the solder paste printing process, and the quality of the subsequent reflow soldering Due to the decisive influence, full plate gold plating is common in high density and ultra-small surface mount processes. 2 In the trial production stage, the factors such as component procurement often do not affect the welding of the board immediately. Instead, it often takes a few weeks or even months to use it. The shelf life of the gold-plated board is higher than that of lead-tin. Together
Gold is many times longer so everyone is happy to adopt it. Furthermore, the cost of gold-plated PCBs in the sample stage is comparable to that of lead-tin alloy plates.
However, with the increasingly denser wiring, the line width and spacing have reached 3-4 MIL. Therefore, the problem of the gold short circuit is brought about:
As the frequency of the signal becomes higher and higher, the effect of signal transmission in multiple coatings due to the skin effect will have a greater effect on signal quality:
Skin effect refers to High-frequency alternating current, the current will tend to concentrate on the surface of the wire.
According to calculations, skin depth is related to frequency:
Other disadvantages of the gold-plated board are listed in the table of the difference between the gold-plated board and the gold-plated board.
Second, why use gold plate
In order to solve the above problems of the gold-plated board, the PCB adopting the gold-immersed board mainly has the following features:
- Due to the different crystal structure formed by Immersion Gold and Gold Plating, Immersion Gold is yellower than Gold Plated Gold, and customers are more satisfied.
- Due to the different crystal structure formed by Immersion Gold and Gold Plating, Immersion Gold is easier to weld than Gold Plating, which will not cause poor welding and cause customer complaints.
- Since there is only nickel-gold on the pads in the gold sink, the signal transmission in the skin effect will not affect the signal in the copper layer.
- Because the gold is denser than the gold plating, the crystal structure is denser and it is not easy to produce oxidation.
5, due to the gold plate only nickel-gold on the pad, so it will not produce gold wire caused by the micro-short.
6, due to the gold plate only the nickel pad on the pad, so the line on the solder mask and the copper layer more firmly.
- The project will not affect the spacing when making compensation.
8, due to the formation of gold and the gold-plated crystal structure is not the same, the stress of the gold plate is more easily controlled, for a bonded product, it is more conducive to the bonding process. At the same time, because the gold is more gold-plated than the gold-plated one, the gold-fingered gold finger does not wear.
- The flatness and service life of the gold plate is as good as that of the gold plate.