Why impedance PCB circuit boards to do

What is the meaning of impedance for PCB circuit boards, PCB impedance circuit board: why do you want to do? Why in this paper, the PCB circuit boards do impedance, expounds the significance of impedance to PCB circuit boards, after the concrete with small make up together to learn about the electronics assembly processing. In a resistor, inductor and capacitor circuit, to hinder the role played by the alternating current is called impedance. Impedance Z is commonly used, it is a complex, real component known as resistance, imaginary part called the reactance, the capacitance in a circuit to hinder the role played by the alternating current (ac) is called the capacitive reactance, inductance in the circuit to hinder the role played by the alternating current is called impedance, capacitance and inductance in the circuit caused by alternating current (ac) in total called reactance. Impedance is the unit of Europe. Caused a lot of products and the users of electronic products ( The bottom of the PCB board or electronic products overall) Poor performance, the main reason is because of poor performance caused by impedance problem, because when unqualified chemical tin plating technology in use process, its for PCB circuit board plating on pure tin tin is not really true, Or the pure metal elemental) But tin compounds ( That no metal simple substance, but metal compounds, oxide or halide, more directly the nonmetal material) Because of PCB circuit board copper foil is the body of the line, on the spot of copper foil is tin plating layer, and through the solder paste (electronic components Or solder wire) Welding on tin coating, in fact, solder paste in the melt state between welding and electronic components and tin plating is metal tin ( The good conductive metal elemental) , so you can simply briefly pointed out that the electronic component is through the bottom of the tin coatings and PCB copper foil of the connection, so the purity of tin coating and the impedance is key; Again, but not before plug in electronic components, we directly use instrument to determine the impedance, the instrument probe (actually Or pens and) At both ends is through the first contact with the bottom of the PCB tin coating on the surface of the copper foil and copper foil to connected with the bottom of the PCB of electric current. So the tin plating is the key, is the key to affect the impedance and a key to PCB whole board performance, also is the key to the easy to be ignored. As is known to all, in addition to the metal elemental, their compounds is a poor conductor of electricity or even not conductive ( Again, this is also existed in the line distribution capacity or spreading capacity key) , so in the tin plating tin compounds or mixtures of conductive not conductive, the ready-made resistivity or future after electrolytic reaction by oxidation, be affected with damp be affected with damp is high resistivity and corresponding impedance ( Enough influence level or signal transmission of the digital circuit,) And its characteristic impedance is not consistent. So will affect the circuit board and the performance of the machine. So, for the present phenomenon of social production, coating material on the bottom of the PCB and performance is the main factor affecting the characteristic impedance PCB whole board and direct reason, but since it has with the variability of the electrolytic coating aging and be affected with damp be affected with damp, so the impedance of suffering influence become more hidden and changeability, the main causes of the hidden: one can not be visible to the naked eye can see, Including the change) , and the second can't be measured, permanent because it changes with time and environmental humidity and variability, so always is easy to be ignored.