What is gold plating in PCB?

Surface treatment of PCB board:
Anti-oxidation, tin spray, lead-free tin spray, immersion gold, immersion tin, immersion silver, hard gold plating, full board gold plating, gold fingers, nickel palladium gold OSP: lower cost, good solderability, harsh storage conditions, time Short, environmentally friendly technology, good welding and smooth.
As the degree of integration of origin electronics IC becomes higher and higher, the number of IC pins becomes more dense. The vertical spraying process is difficult to flatten the thin pads, which brings difficulty to Surface-Mount (SMT) & BGA Assembly; in addition, the shelf life of the sprayed PCB is very short.
The gold-plated PCB just solves these problems:
1. For Surface-Mount (SMT) &BGA Assembly, especially for 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, it has a decisive influence on the quality of the subsequent Wave Solder for PCBA Therefore, the whole board gold plating is common in the high-density and ultra-small surface mount process.
2. In the trial production stage, the influence of the purchase of Electronic Components and other factors is often not that the PCB is soldered right away, but often has to wait for several weeks or even months before using it. The shelf life of the gold-plated board is more than Pewter is many times longer, so everyone is happy to use it.
Besides, the cost of gold-plated PCB in the sample stage is almost the same as that of lead-tin alloy board.
But as the wiring becomes denser, the line width and spacing have reached 3-4MIL.
This brings about the problem of gold wire short circuit: as the frequency of the high frequency board signal becomes higher and higher, the transmission of the high frequency mixing pressure plate signal in the multi-plated layer due to the skin effect has more obvious influence on the signal quality.
The skin effect refers to the alternating current of the High frequency board, the current will tend to concentrate on the surface of the wire to flow. According to calculations, skin depth is related to frequency.