Vacuum laminating machine, reduce the pressure to reduce the flow of glue, try to maintain more resin amount, because the resin affects εr, resin preservation more, εr will be lower. Control laminate thickness tolerances. Because the thickness of the PCB board is not uniform, it indicates that the change in the thickness of the medium will affect Z0.

　　Strictly according to the customer requirements of the PCB board plate type, the model is wrong, εr is wrong, the board thickness is wrong, the manufacturing process of PCB is all right, and the same is scrapped. Because Z0 is greatly affected by εr, the finished multilayer board should try to avoid water absorption, because the εr of water = 75, which will bring a great drop and instability effect on Z0.

　　The solder resistance of the PCB board surface will reduce the Z0 value of the signal line by 1 to 3Ω, and theoretically the solder resistance thickness should not be too thick, in fact, the impact is not very large. The surface of the copper wire is in contact with air (εr = 1), so the Z0 value is high. However, after welding resistance, the Z0 value will decrease by 1 to 3Ω, because the εr of welding resistance is 4.0, which is much higher than the air.

　　Special reminder: the inner plate must find out the wire gap, convex, for 2GHZ high-speed signal, even 0.05mm gap, must be scrapped; Controlling the inner line width and defects is the key.

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