High precision multi - layer PCB circuit board processing

High precision multi - layer PCB circuit board processing

With the development of modern electronic technology and the high-speed and integrated chip, a variety of electronic equipment system inside and outside the electromagnetic environment is more complex, so multi-layer PCB processing is particularly important. Multi-layer circuit boards compared to single-sided, double-sided panels require higher technology and processing technology. Is multi-layer pressure, high-quality multi-layer PCB processing. Multi-layer printed circuit boards, precision multi-layer circuit board production, recommended Shenzhen million Chong Hing Electronics Co., Ltd. In addition, the overall price of multilayer boards is also based on the basis of multi-layer proofing proof, only the sample qualified, then the product can be mass production; if the product size comparison Large, they can meet the process of proofing in the entire multi-layer board, you need to ensure that each revision to meet the conditions and requirements Caixing, or inventory can only be used as a scrapped to deal with, this is really a very painful comprehend.

As shown in Figure 1, the printed circuit board impedance characteristics

According to the signal transmission theory, the signal is a function of time, distance variable, so the signal on each part of the connection is likely to change. Therefore, determine the AC impedance of the connection, that is, the change in voltage and the ratio of the current to the transmission line characteristic impedance (characteristic impedance): the characteristic impedance of the transmission line is only related to the characteristics of the signal wiring itself. In the actual circuit, the resistance of the wire itself is less than the distributed impedance of the system. In the high frequency circuit, the characteristic impedance depends mainly on the distributed impedance of the unit distributed capacitance and the unit distributed inductance. The characteristic impedance of the ideal transmission line depends only on the unit of distributed capacitance and the unit distributed inductance.

2, printed circuit board characteristic impedance calculation

The rising edge of the signal and the ratio of the time it takes for the signal to be transmitted to the receiver determines whether the signal connection is considered as a transmission line. The specific relationship between the following formula can be explained: If the PCB board wire length greater than l / b can be between the signal connection wire as a transmission line. From the signal equivalent impedance calculation formula, the impedance of the transmission line can be expressed by the following formula: in the case of high frequency (tens of megahertz to hundreds of megahertz) to meet wL >> R (of course, the signal frequency is greater than 109Hz range, then Considering the skin effect of the signal, it is necessary to study this relationship carefully.) For a given transmission line, the reflection of the characteristic impedance as a constant signal is due to the characteristic impedance of the drive and transmission lines of the signal and the impedance of the receiver Inconsistent caused by the CMOS circuit, the signal drive side of the output impedance is relatively small, for dozens of Europe. While the input impedance of the receiver is relatively large.

3, printed circuit board characteristic impedance control

The characteristic impedance of the wire on the printed circuit board is an important indicator of the circuit design. Especially in the PCB design of the high frequency circuit, it is necessary to consider whether the characteristic impedance of the wire and the characteristic impedance required by the device or signal are consistent and matched. , There are two concepts in the reliability design of the PCB design that must be noted.

As shown in Figure 4, the printed circuit board impedance control

There are various signals in the conductor in the circuit board. When the transmission rate must be increased, the circuit itself must be changed due to the different factors such as etching, stack thickness, wire width and so on, which will cause the impedance to change. Signal distortion, so the high-speed circuit board conductor, the impedance value should be controlled within a certain range, known as the "impedance control." The factors that affect the impedance of the PCB trace are the width of the copper wire, the thickness of the copper wire, the dielectric constant of the medium, the thickness of the medium, the thickness of the pad, the path of the ground, and the alignment of the traces. So in the design of PCB must be on the board to control the impedance of the line in order to avoid the signal reflection and other electromagnetic interference and signal integrity issues to ensure the practical use of PCB board stability. PCB board microstrip line And the calculation of the stripline impedance can refer to the corresponding empirical formula.