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Why use a gold-plated sheet:
As ICs become more integrated, more more IC pins become denser. However, it is difficult for the vertical spraying process to flatten the thin pads, which brings difficulty to the placement of the SMT; in addition, the shelf life of the sprayed board is short. The gold-plated sheet just solves these problems:
1. For surface mount technology, especially for 0603 0402 ultra-small surface mounts, because the pad flatness is directly related to the quality of the solder paste printing process has a decisive influence on the quality of the subsequent reflow soldering, so the entire board Gold plating is common in high-density ultra-small surface-mount processes.
2. In the trial production stage, due to the influence of component procurement other factors, it is often that the board is welded immediately after it comes, but often it takes several weeks even months to use it. The shelf life of the gold-plated plate is longer than that of lead. Tin alloys are many times longer, so everyone is happy to use them. Besides, the cost of gold-plated PCBs in the sample stage is similar to that of lead-tin alloy boards. But as the wiring becomes denser denser, the line width pitch have reached 3-4 MIL. Therefore, the problem of short circuit of the gold wire is brought. As the frequency of the signal becomes higher higher, the signal transmission in multiple coatings due to the skin effect has a more obvious effect on the signal quality. (Skin effect refers to high-frequency alternating current, current will tend to concentrate on the surface of the wire. According to calculations, skin depth is related to frequency.)
Why use an immersion gold plate:
In order to solve the above problems of gold-plated plates, PCBs using immersion gold plates mainly have the following characteristics:
1. Because the crystal structure formed by immersion gold gold plating is different, immersion gold will be golden yellow yellower than gold plating, customers are more satisfied.
2. Because the crystal structure formed by immersion gold gold plating is different, immersion gold is easier to weld than gold plating, which will cause poor welding cause customer complaints.
3. Because the gold plate only has nickel-gold on the pad, the signal transmission in the skin effect is that the copper layer will affect the signal.
4. Because immersion gold has a denser crystal structure than gold plating, it is easy to produce oxidation.
5. As the gold plate only has nickel gold on the pads, it will produce short gold wires.
6. Because the gold plate only has nickel gold on the pad, the combination of solder mask copper layer on the circuit is stronger.
7. The project will affect the spacing when making compensation.
8. Because the crystal structure formed by immersion gold gold plating is different, the stress of the immersion gold plate is easier to control, for products with bonding, it is more conducive to bonding processing. At the same time, because the immersion gold is softer than the gold plating, the immersion gold plate is wear-resistant as a gold finger.
9. The flatness standby life of immersion gold plates are as good as those of gold-plated plates. pcb customization
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