Knowledge of PCB routing board impedance

Impedance about PCB circuit board meaning is, PCB circuit board what to do impedance?

What is impedance

The existence of resistance, inductance, and the capacity of the path, for the exchange of electricity played a barrier action called impedance. Impedance rare with Z, is once singular, the real part is called the resistance, the imaginary part is called the internal resistance, the internal and internal capacity in the path of the exchange of electricity played by the barrier action called capacitive reactance, inductance in the path of the exchange of electricity played by the barrier action called inductive reactance, the capacity and inductance in the path of the exchange of electricity caused by the barrier action called internal resistance. The impedance sector is O.

Impedance type

(1) Characteristic impedance

In computer, wireless communication and other electronic message goods,printed board route transmission of energy, is a square wave signal formed by voltage and time (called pulse), it encountered the barrier is called characteristic impedance.

(2) differential impedance

The driving end outputs two different signal waveforms with the same polarity, which are respectively transmitted by two differential wires. The two differential signals at the absorbing end are subtracted. Differential impedance is simply the impedance Zdiff between two lines.

(3) odd-mode impedance

The impedance of one of the two lines to the ground Zoo, the impedance values of the two lines are diverging.

(4) even mode impedance

The driving end outputs two different signal waveforms of opposite polarity and connects the two lines to the simultaneous impedance Zcom.

(5) common-mode impedance

The impedance of one line of the two lines to the ground is Zoe, and the impedance values of the two lines are different, generally larger than the odd-mode impedance.

PCB route board what to do impedance

PCB circuit board impedance refers to the resistance and to the internal resistance of the parameters for the exchange of electricity plays an obstacle role. In pcb circuit board consumption, impedance solution is no less. The reasons are as follows:

1, PCB circuit board (bottom of the board) to consider the plug device electronic components, plug in after thinking about thermal conductivity function and signal transmission function, because the lower the impedance will request the better.

2, PCB circuit board is in the process of consumption to experience copper, silver plated tin (or electroless plating, or hot spray tin), solder joints and other process manufacturing links, and the data used in the link must guarantee the resistivity of the bottom, the ability to guarantee the impedance of the route board to reach the quality of the goods, can be deformed operation.

3. Tin plating of PCB circuit board is the most simple central result in the manufacture of the whole route board, and it is the key link of the reaction impedance. The biggest disadvantage of electroless tin layer is easy to change face (both easy oxidation or deliquescence), poor brazing, will lead to the route plate difficult riveting, impedance stunt caused by poor thermal conductivity function or the function of the whole plate is not stable.

4, PCB circuit board in the superconductor will have all kinds of signal transmission, when the transmission rate must improve its frequency, route itself if the seal cutting, laminated thickness, wire amplitude and other elements are not the same, will form impedance is not worth the change, so that the signal is realistic, resulting in circuit board use function drop, because the demand to grasp the impedance value is within the scope.

Impedance refers to PCB circuit board

For the electronic industry, according to the internal investigation, the most vital weakness of the chemical tin layer is easy to change face (easy oxidation or moisture), poor brazing performance leads to difficult riveting, impedance stunt caused by poor thermal conductivity function or the whole board function is not stable, easy long tin must lead to PCB circuit board short circuit or even incination or fire.

At first, when the entire political and legal consumption industry stagnated to a certain level, many of the initial participants were often due to mutual plagiarism. Indeed, the whole enterprise itself did not have the development or founding power, because the electronic goods (the bottom of the route board or the whole electronic goods) that formed many goods and their users were not good. The least important reason for poor performance is impedance, because when no decent electroless tin plating skill is being used, the tin plated for PCB boards is not really pure tin (or pure non-metallic element), but a tin compound (i.e., basically no error-metal element, and error-metal complex, Oxides or halides, more indirectly ascribe to the spirit of nonnonmetals) or mixtures of tin compounds and tin nonmetallic elements, but are hardly detectable by the naked eye alone... .

Because the main route of the PCB circuit board is copper foil, is the solder joint of the copper foil is tin layer, and the electronic parts is after solder paste (or solder line) riveted under the tin layer, in reality, solder paste is melting form riveted to the electronic parts and the error between the tin coating metal tin (namely, excellent non-metallic element of heat conduction), because it can be easily pointed out, Electronic components are connected with copper foil at the bottom of the PCB board after the tin coating, because the purity of the tin coating and its impedance is key; Also, but no plug electronic parts in advance, we indirectly use the instrument to detect the impedance, the instrument probe (or called the pen) at both ends of the first contact with the copper foil at the bottom of the PCB board and then copper foil at the bottom of the PCB board to connect the DC. Because the tin coating is the key, is the key of the reaction impedance and the key of the reaction PCB circuit board function, is also easy to be neglected.

Except for the elemental metal, the composite is electric, has no good superconductor or even does not conduct heat (which is also the key to the formation of the route with the dispersion or propagation of quantitation), because the tin coating has such a heat-like rather than heat-conducting compound or mixture of tin, Its natural resistivity or the resistivity after the electrolytic response caused by oxidation or freezing in the future and its corresponding impedance are equally high (sufficient to reflect the level or signal transmission in the digital channel) and its characteristic impedance is not different. Because it will reflect the function of the route plate and its parts.

Because, on the current political consumption scene, PCB board bottom coating spirit and function is the reaction printed circuit board characteristic impedance of the least reason and the most indirect reason, but because of its existence is with the plating aging and the change of freezing electrolysis, because the impedance of the crisis reaction becomes more and more.