When pressing, PP and copper foil are added on both sides of the double panel, and the high temperature and high pressure are pressed into a multi -layer board. In short, the four -layer board has an inner layer. In terms of process, some circuits will be carved and suppressed in the inner layer. Double -panels can directly cut out the drilling of the factory board.

　　The four -layer board refers to the printing circuit board. PCB is made of four -layer glass fiber, which can reduce the cost of PCB, but the efficiency is very low.

　　Although it is difficult to get the four -layer PCB board by observing the cross section of PCB, few people have such vision. However, you can identify the four -layer board by observing the guide hole. If the same guide hole, or the motherboard or the graphics card can be found on both sides of the PCB, if the position of the guide hole cannot be transmitted, it is a four -layer board.

　　The four -layer circuit board is made of combination on the basis of double panels. PP and copper foil are added on both sides of the double panel when pressing, and then the multi -layer board is synthesized by high temperature and high pressure. In short, the four -layer board has an inner layer. In terms of process, some circuits will be etched through the inner layer and then press it. Double -panels can directly cut out the drilling of the factory board.

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