Why Do PCB Boards Do Impedance?

Why do PCB boards do impedance?

Impedance – in fact, refers to the resistance and the parameters of the pair of reactance, because the PCB line to consider the plug-in installation of electronic components, plug-in after the consideration of conductivity and signal transmission performance and other issues, so it is inevitable that the lower the impedance the better, the resistivity should be lower than per square centimetre 1 × 10 of the minus 6 times the following.

On the other hand, PCB board in the production process to go through the copper sinking, tin plating (or chemical plating, or thermal spray tin), connectors and other parts of the link and the materials used in this link must ensure that the bottom of the resistivity, in order to ensure that the overall impedance of the PCB board is low in order to comply with the requirements of product quality, or else the circuit board will not operate normally.

The electronics industry as a whole, PCB circuit board factory in the tin-plating link is the most problematic, is the impact of the impedance of the key links, because the circuit board tin-plating link, is now popular to achieve the purpose of tin-plating using chemical tin-plating technology, but we as the electronics industry as a recipient of electronic industry, or PCB board production and processing industry for more than 10 years of contact and observation.

For the electronics industry, according to the line of investigation, the most fatal weakness of the chemical tin layer is easy to discolour (both easy oxidation or deliquescence), poor brazing leads to difficult to weld, impedance is too high leading to poor conductivity or the whole board performance instability, easy to grow tin whiskers lead to PCB line short-circuiting or even burnt or on fire events.

The main line of PCB circuit board is copper foil, copper foil in the solder joints is the tin layer, and electronic components is through the solder paste (or solder line) welded on top of the tin layer, in fact, solder paste in the melting state of soldering to the electronic components and tin plating layer between the tin metal (i.e., conductive metal monomers), so it can be simple and concise to point out that the electronic components are plated with tin plating layer with the bottom of the PCB board and then the copper foil Connection.

So the purity of the tin plating layer and its impedance is the key; but not before the connection of electronic components, directly with the instrument to detect the impedance, in fact, the instrument probe (or known as the meter pen) ends are also through the first contact with the circuit board board at the bottom of the surface of the copper foil of the tin plating layer and then with the bottom of the PCB board copper foil to connect the current. So the tin coating is the key, is the key to affect the impedance and affect the performance of the circuit board board, but also easy to be ignored key.

In addition to metal monomers, their compounds are poor conductors of electricity or even non-conductive (which is also caused by the existence of distribution capacity in the line or transmission capacity of the key), so the tin plating layer in the presence of this kind of seemingly conductive and non-conductive compounds or mixtures of tin, its ready-made resistivity or future oxidation, the electrolytic reaction of moisture and its corresponding resistivity and impedance is quite high (enough to affect the level or signal transmission of the digital circuits). level or signal transmission in digital circuits), and its characteristic impedance is not consistent. This affects the performance of the circuit board and the machine as a whole.

In terms of the current social production phenomenon, pcb board on the bottom of the plating material and performance is to affect the PCB board characteristics of the impedance of the most important reason and the most direct reason, but also because of the plating with the aging and moisture electrolysis of the variability of the impedance so that its impedance to produce a worry about the impact of the impact of the more hidden and changeable, and the main reason for its concealment lies in the following: the first can not be seen by the naked eye, and the second can not be constant measurement, because it has with time and ambient humidity and the change of the impedance of the board and the performance of the machine. Because it has the variability with the change of time and environmental humidity, so it is always easy to be ignored.

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