Impedance PCB circuit board: why do you want to do
The impedance PCB circuit boards, PCB circuit board: why do you want to do the parameters of the impedance is refers to the resistance and reactance, blocking effect of alternating current (ac).
In PCB circuit board production, impedance processing is necessary.
Reasons are as follows: 1, PCB line (
Want to consider the plug-in installed electronic components, plug after considering the conductive performance and signal transmission performance problems, so will demand impedance is lower, the better, the resistivity is lower than 1 & TImes per square centimeter;
2, PCB circuit board in the process of production will experience heavy copper, tin plating,
Or chemical plating, thermal spray tin)
Link of the production process such as connectors, solder, and these materials are used in the link must ensure that the bottom of the resistivity, to guarantee the overall low impedance circuit board meet product quality requirements, can run normally.
3, PCB circuit board of the tin plating is the most vulnerable to the circuit board production, is a key link in the process of impedance.
Electroless tin the biggest flaw is easy to change color,
Both easy oxidation or deliquescence)
Sex differences, brazing, will lead to problems in terms of circuit board welding, high impedance leads to poor conductivity or the whole board performance instability.
4, PCB circuit board in the conductor will have all kinds of signals, when the transmission rate and to raise its must raise its frequency, if the line itself due to factors such as etching, laminated thickness, wire width is different, will cause resistance to change, make the signal distortion, led to the decrease of the circuit board using performance, so they need to control the impedance value within a certain range.
Second, the meaning of the impedance for PCB for the electronics industry, according to industry, 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
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.