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First, PCB board surface treatment
Anti-oxidation, tin spray, lead-free tin spray, immersion gold, immersion tin, immersion silver, hard gold plating, full plate gold plating, gold finger, nickel-palladium OSP: lower cost, good solderability, harsh storage conditions, time Short, environmentally friendly technology, good welding smooth.
Tin spraying: Tin spraying plates are generally multilayer (4-46 layers) high-precision PCB samples, which have been used by many large domestic telecommunications, computers, medical equipment, aerospace companies research units. All the signals between the upper part the memory slot are transmitted through gold fingers.
The gold finger is composed of many golden yellow conductive contacts. Because the surface is plated with gold the conductive contacts are arranged like fingers, it is called a "golden finger". Gold fingers are actually coated with a layer of gold on a copper-clad board through a special process, because gold is extremely resistant to oxidation has a strong conductivity. However, due to the expensive price of gold, most of the current memory is replaced by tin plating. Tin materials have been popular since the 1990s. At present, almost all "golden fingers" of motherboards, memory graphics cards are used. For tin materials, only some high-performance server / workstation accessories will continue to use gold plating, which is naturally expensive.
Why use gold plate
As ICs become more integrated, more more IC pins become denser. However, it is difficult for the vertical solder spray process to blow the thin pads flat, which brings difficulty to the placement of SMT; in addition, the standby life of the solder spray board is very 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 factors such as component procurement, it is often that the board is welded immediately after it comes, but often it takes several weeks even months to use it. The standby life of gold-plated plates is much longer than that of lead-tin alloy Therefore, everyone is willing to adopt it. Besides, the cost of gold-plated PCB in the sample stage is similar to that of lead-tin alloy plate.
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 about: As the frequency of the signal is getting higher higher, the signal transmission in multiple coatings due to the skin effect has a more obvious impact on the 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.
Third, 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. The crystal structure formed by immersion gold gold plating is different. The immersion gold will be golden yellow yellower than gold plating, the customer is more satisfied.
2. The crystal structure formed by immersion gold is the same as that of gold plating. Compared with gold plating, immersion gold is easier to weld without causing poor welding causing customer complaints.
3. There is only nickel-gold on the pad of the immersion gold plate. The signal transmission in the skin effect is that the copper layer will affect the signal.
4. The crystal structure of immersion gold is denser than gold plating, it is easy to produce oxidation.
5. The immersion gold plate only has nickel-gold on the pads, so it will produce short gold wires.
6. The immersion gold plate has nickel-gold only on the pads, so 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.
Fourth, immersion gold plate VS gold plate
In fact, there are two types of gold plating processes: one is electroplated gold the other is immersion gold.
For the gold plating process, the effect of tin on it is greatly reduced, the effect of tin on Shen gold is better; unless the manufacturer requires binding, otherwise most manufacturers will choose the immersion gold process! Generally common In the case of PCB surface treatment is the following: gold plating (plated gold, immersion gold), silver plating, OSP, tin spray (lead lead-free), these are mainly for FR-4 CEM-3 other plates In terms of the paper base material, there is also a rosin-coated surface treatment method; if the tin is good (the tin is good), the reasons for the production of the solder paste other patch manufacturers material technology are excluded.
The advantages disadvantages of several methods of surface treatment are their own strengths weaknesses!
In terms of gold plating, it can make the PCB be stored for a long time, it is less affected by the external temperature humidity (compared to other surface treatments), it can generally be stored for about one year; the surface is tinned, followed by OSPL, Pay attention to the storage time of these two surface treatments in ambient temperature humidity. Circuit board manufacturer
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