With the increasing integration of IC, IC feet are more and more compact. Vertical tin spraying process is difficult to smooth the thin solder pad, which brings difficulties to SMT mounting. In addition, compared with gold plated circuit board, the shelf life of tin spraying board is very short. Gold plated circuit boards just solve these problems: 1. For surface mounting process, especially for 0603 and 0402 super-miniature surface mounting, the smoothness of solder pad is directly related to the quality of solder paste printing process, and plays a decisive role in the quality of reflow soldering. Therefore, gold plating on whole plate is common in high density and super-miniature surface mounting process. 2. In the trial-manufacture stage, the influence of component purchasing and other factors is not that the board will be welded immediately, but that it is often used several weeks and months later. The shelf life of the gold plated circuit board is many times longer than that of the lead-tin alloy, so everyone is willing to adopt it. Besides, the cost of the gold-plated PCB in the sample stage is almost the same as that of the lead-tin alloy plate. But as the wiring becomes more and more dense, the widths and spacing have reached 3-4 MIL. Therefore, it brings the problem of short circuit of gold wire: with the increasing frequency of the signal, the effect of skin effect on the quality of the signal is more obvious. Skin effect refers to: high frequency AC current, the current will tend to concentrate on the surface of the wire flow. According to the calculation, the skin depth is related to the frequency.