PCB Fabrication

The significance of impedance to PCB

by:A-TECH      2020-05-14
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. It is understood that the first domestic research of electroless tin as kunming university of science and technology in the early 1990 s, followed by the late 90 s with modest chemical (guangzhou 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 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) . 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 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 reason for its hidden lies in: 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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