Factors affecting the contact impedance of IC sockets

　　In recent years, due to the improvement and application of IC socket integration, its signal transmission frequency and speed have gradually become higher. Therefore, in the printed board wire, after the signal transmission (emission) reaches a certain value, it will suffer from the printed board. The influence of wires can cause serious distortion or complete loss of the transmitted signal. This means that the "thing" "circulated" by the PCB wires is not the current, but the transmission of square wave signals or pulses in energy.

　　1.What is impedance?

　　Impedance is defined as the resistance encountered by conducting alternating current (AC) in a wire

　　The definition of characteristic impedance is the transmission of a square wave signal or pulse signal flowing in the PCB circuit, and the resistance suffered by this signal during transmission is called the characteristic impedance.

　　Differential impedance definition: refers to the signal resistance interference between two signals in the same layer.

　　Definition of Coplanar Impedance: It is a kind of differential impedance, but the signal transmission and the distance between its adjacent copper surfaces will have a corresponding influence.

　　2. PCB transmission line

　　The transmission line of PCB is mainly composed of signal line, dielectric layer and reference layer. (If the signal propagates in the wire, if the length of the wire is close to 1/7 of the signal wavelength, the wire is regarded as a transmission line. Wavelength = beam/frequency.

　　Er: Also called DK (dielectric constant), which is the relative capacitance. Different materials have different Er values under different measurement conditions, which also have a great influence on the propagation speed of the signal.

　　3. Why do you want to control impedance?

　　Although any component has a high signal transmission frequency, after transmission through the PCB wire, the original high transmission frequency will drop or time delay. Therefore, the shorter the wire length, the better.

　　In addition, it is very beneficial to increase the PCB wiring density or shorten the wire size. However, as the component frequency increases or the pulse period decreases, the wire length approaches a certain range of signal wavelength (speed). At this time, when the component is transmitted on the PCB wire, significant "distortion" will appear.

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