Characteristic impedance is a very important parameter in PCB (Printed Circuit Board) design.2 oz copper thickness in mm It is the ratio of the resistance and inductance of a signal on a transmission line and is used to characterize the signal during transmission. So, what factors affect the characteristic impedance of PCB circuit boards? There are several factors: dielectric thickness H, copper thickness T, the width of the alignment W, the spacing of the alignment, the dielectric constant Er of the material selected for the stacked layer and the thickness of the solder resist.

First, the dielectric thickness is an important factor affecting the characteristic impedance. Increasing the dielectric thickness increases the characteristic impedance. This is because the greater the thickness of the dielectric, the slower the signal propagates through the dielectric, which increases the resistive component, resulting in an increase in the characteristic impedance.

Secondly, line width is also a key factor affecting the characteristic impedance. Increasing the line width decreases the characteristic impedance, while decreasing the line width increases the characteristic impedance. This is because the wider the line width, the larger the area over which the current flows, the smaller the resistive component, resulting in a decrease in characteristic impedance; conversely, the narrower the line width, the smaller the area over which the current flows, the larger the resistive component, resulting in an increase in characteristic impedance.

Third, copper thickness also affects the characteristic impedance.plated through hole vs via Reducing the wire thickness increases the characteristic impedance, while increasing the wire thickness decreases the characteristic impedance. This is because the thinner the wire thickness, the larger the area over which the current flows, the resistive component decreases, resulting in an increase in characteristic impedance; on the contrary, the thicker the wire thickness, the smaller the area over which the current flows, the resistive component increases, resulting in a decrease in characteristic impedance.

Fourth, the dielectric constant also has an effect on the characteristic impedance. Increasing the dielectric constant decreases the characteristic impedance, while decreasing the dielectric constant increases the characteristic impedance. The dielectric constant is mainly controlled by the material. Different materials have different dielectric constants, and choosing the right material can effectively control the characteristic impedance.

Finally, the thickness of the soldermask also has an effect on the characteristic impedance. Printing on the soldermask will reduce the outer layer impedance. Under normal circumstances, printing one pass of soldermask will drop the single-ended by 2 ohms and the differential by 8 ohms. Printing two times of soldermask will double the drop value, while printing three times or more, the impedance value no longer changes.

In the PCB with high-frequency signal transmission, the characteristic impedance control is particularly important. Because the PCB not only plays the role of current conduction, but also bears the task of signal transmission. With the development of high-frequency and high-speed electronic products, PCB circuit performance must ensure that the signal does not reflect in the transmission process, to maintain signal integrity, no distortion. Therefore, the characteristic impedance has become one of the core factors in solving the problem of signal integrity.

When electronic equipment (such as computers, communication switches, etc.) operation, the signals issued by the driving components need to reach the receiving components through the PCB signal lines. In order to ensure the integrity of the signal, the characteristic impedance of the signal line of the PCB must be matched with the "electronic impedance" of the head and tail components. When the length of the transmission line is greater than or equal to 1/3 of the rise time length, the signal will be reflected, then you need to consider the impact of the characteristic impedance.

In summary, the dielectric thickness, line width, copper thickness, dielectric constant and soldermask thickness and other factors will have an impact on the characteristic impedance of the PCB circuit board. In the design and manufacture of PCB, according to the specific application needs and requirements, need to reasonably select and control these parameters, in order to ensure the performance and stability of the circuit.