The meaning of the impedance for PCB PCB proofing

What is the meaning of impedance for PCB circuit boards, PCB circuit board why want to do impedance. Impedance - — Actually refers to the resistance and reactance parameters, because the PCB line ( Bottom) Want to consider the plug-in installed electronic components, plug after considering the problem such as electric conductivity and the signal transmission performance, so inevitable requirement impedance is lower, the better, the resistivity is lower than 1 x 10 per square centimeter of negative power 6 below. PCB in the process of production, on the other hand, will experience heavy copper, tin plating, Or chemical plating, thermal spray tin) , connector soldering and the link, all must ensure that the bottom of the resistivity of materials, to guarantee the whole PCB impedance low and conform to the requirements of the product quality, otherwise the circuit board will not be able to run normally. In the electronics industry as a whole, PCB circuit board factory in tin link is one of the most vulnerable, is a key link in the process of impact impedance, tin link for PCB, is now popular use chemical tin plating technology to realize the purpose of tin plating, but we as by employing of electronics industry, processing industry of electronic or PCB production contact and observation for more than 10 years, in domestic can do a good job in electroless tin ( Used for PCB board or electronic tin plating) Not many enterprises because of the chemical tin plating technology is a rising star in China, and the technology level of the enterprises is uneven. For the electronics industry, according to industry research, chemical tin plating layer is the most fatal weakness is easy to change color, Both easy oxidation or deliquescence) , poor soldering lead to difficult to welding, high impedance leads to poor conductivity or the whole board performance is not stable, easy to long tin whisker cause the PCB short circuit and burned or fire events. The first domestic research of electroless tin as kunming university of science and technology in the early 1990 s, then in the late 90 s of guangzhou with modest chemical ( Enterprise) Inline, up to now, 10 years have recognized the two agencies is to do the best. Among them, according to our contact screening for many enterprises investigation, experimental observation and long endurance test, confirm with modest chemical tin plating layer is the pure tin of low resistivity layer, conductive and brazing quality can ensure the high level, it is no wonder that they dare to external guarantee its coating without any closed and its agent protection cases, can keep a year don't change color, no bubbles, no peeling, permanent long tin whisker. Later, when the development of the society as a whole industry to a certain extent, many participants tend to belong to copying each other later, in fact, quite a number of research and development of enterprise itself and no or pioneering ability, so, caused a lot of products and the users of electronic products ( The bottom of the PCB PCB board or electronic products overall) Poor performance, poor performance caused by the most main reason is because the impedance of 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) With tin or tin compounds a mixture of simple substance, but it is hard to find with the naked eye. PCB circuit board copper foil, is the body of the line on the copper foil of solder joints is tin plating layer, and the electronic component is through the solder paste ( 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. So the purity of tin coating and the impedance is key; Again, but not before plug in electronic components, direct use instrument to determine the impedance, the instrument probe (actually Or pens and) At both ends is by first contact with the bottom of the PCB board of tin coating on the surface of the copper foil and copper foil to connected with the bottom of the PCB current. So the tin plating is the key, is the key to affect the impedance and circuit board is the key to the whole board performance, also is the key to the easy to be ignored. In addition to the metal simple substance, the compound is a poor conductor of electricity or even non-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. In terms of current phenomena 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 the most 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: first by the naked eye can't see, Including the change) , the second cannot be invariant measure, because it has change with time and environmental humidity and variability, so always is easy to be ignored. 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