What are the functions of gold, silver and copper in PCB?
PCB is used as the main part of electronic-related products in various fields and is the carrier for electrical connections of electronic components. PCBs contain higher-cost metals. For example, an average smartphone contains 0.05g of gold, 0.26g of silver, and 12.6g of copper. The outer layer of PCB mainly comes in three colors: gold, silver, and light red. Gold costs the most, followed by silver and light red. However, the circuits inside the circuit board are mainly pure copper, that is, bare copper boards.
Why is high-cost metal needed on PCB?
Components need to be soldered on the PCB surface, requiring a portion of the copper layer to be exposed for soldering. These exposed copper layers are called pads. The pads are generally round and have a small area. Therefore, after applying the solder resist, the only thing exposed to the air is the copper on the pad, so this part It needs to be protected from oxidation. Copper is very easily oxidized. If the copper on the pad is oxidized, it will not only be difficult to weld, but the resistivity will also increase greatly. Therefore, plating the pad with inert metal gold or covering its surface with a layer of silver through a chemical process can better protect the pad.
Gold on PCB
Gold is used in immersed gold PCB and gold-plated PCB. Although only a thin layer of plating is required, it can account for 10% of the cost of the circuit board. The use of gold as the plating not only provides a good connection effect, but also meets the anti-corrosion properties. Even the gold fingers of memory modules that have been used for several years are still in good condition.
Silver on PCB
The cost of using immersion silver is lower than that of gold. Immersion silver has good flatness and contact properties, but it has defects such as easy tarnishing and solder joint voids. If the product requirements are not that high, Chen Yin is a good choice.
Copper on PCB
PCB copper-clad board is a plate-shaped material made by impregnating glass fiber cloth or other reinforcing materials with resin on one side or covering both sides with copper foil and hot pressing. Taking fiberglass cloth-based copper-clad laminate as an example, its main raw materials are copper foil, fiberglass cloth, and epoxy resin, accounting for approximately 32%, 29%, and 26% of the product cost respectively. Copper clad laminate is the basic material of PCB. The conductors used in PCB are made of thin foil-shaped refined copper, which is copper foil in a narrow sense.
There are gold, silver, and copper metals on the PCB in order to have better electrical performance and corrosion resistance. Reasonable selection of the process will greatly improve the life and performance of the product.
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