PCB News - Influence of PCB machining on impedance control and its solution

China is now in the good situation of economic construction as the center and reform and opening up, the annual growth rate of the electronic industry will be more than 20%, the printed circuit board industry will follow the trend of the entire electronic industry will also rise, and more than 20% growth rate.The technological revolution and industrial structure change in the world electronic industry are bringing new opportunities and challenges for the development of printed circuit.With the miniaturization, digitization, high-frequency and multifunctional development of electronic equipment, printed circuit, as a metal conductor in the interconnection of electrical components in electronic equipment, is not only a question of current flow or not, but also as a signal transmission line.That is to say, the electrical test of PCB for the transmission of high frequency signal and high speed digital signal should not only measure whether circuit break and short circuit meet the requirements, but also measure whether the characteristic impedance is within the specified qualified range.Only these two directions are qualified, the circuit board can meet the requirements.

The circuit performance provided by printed circuit board must be able to make the signal transmission process without reflection phenomenon, signal integrity to reduce transmission loss to play the role of impedance matching, so as to get a complete, reliable, accurate, no interference, noise transmission signal.In this paper, the characteristic impedance control of multilayer laminates with surface microstrip line structure is discussed.

1. Surface microstrip line and characteristic impedance

2. The dielectric constant of the material and its influence

3. Influence of wire width and thickness

4. Influence of medium thickness H

Conductor in the actual production of width, thickness and dielectric constant of the insulating material and the thickness of the insulating medium change characteristic impedance values change will cause a little, the characteristic impedance values also produces with other factors, so in order to realize the control of the characteristic impedance producers must understand the factors that result in the change of characteristic impedance value, master the practical production conditions, according to the requirements of the designer put forward adjusting the process parameters, the change of the allowed tolerance range, to achieve the desired impedance values.