Difference between PCB gold plated and immersion gold plate
As ICs become more integrated, more and 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 the surface mount process, especially for 0603 and 0402 ultra-small surface mounts, because the pad flatness is directly related to the quality of the solder paste printing process and has a decisive influence on the quality of the subsequent reflow soldering, Gold plating on the entire board is common in high-density and ultra-small surface-mount processes.
(2) In the trial production stage, due to factors such as component procurement, it is often not that the board is soldered immediately after it comes, but often it takes several weeks or even months to use it, and the shelf life of the gold-plated board It is many times longer than lead-tin alloy, so everyone is happy to use 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 and denser, the line width and 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 becomes higher and 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.
2. 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 and gold plating is not the same, immersion gold will be golden yellow and yellower than gold plating, and customers are 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 welding failure and cause customer complaints.
(3) Because only the pads of the immersion gold plate have nickel gold, the signal transmission in the skin effect is that the copper layer will not affect the signal.
(4) Because immersion gold has a denser crystal structure than gold plating, it is not easy to produce oxidation.
(5) Because the gold plate only has nickel and gold on the pads, it will not produce short gold wires.
(6) Because the gold plate only has nickel and gold on the pads, the combination of solder mask and copper layer on the circuit is stronger.
(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 plate is easier to control, and it is more conducive to bonding processing for products with bonding. At the same time, because the immersion gold is softer than the gold plating, the immersion gold plate is not wear-resistant as a gold finger.
(9) The flatness and standby life of the immersion gold plate are as good as those of the gold-plated plate.