There are many types of impedances, and their classification methods are also different. Impedance is generally classified according to the number of wire diameters and transmission methods:
Classification of impedance control
Single ended impedance: composed of a line and a ground layer.
Differential impedance: composed of two lines and a geological layer.
According to different modes of dissemination, it can be divided into:
A microstrip line is an impedance line that is parallel to the ground plane on one side, separated by a dielectric layer in the middle, and has a solder mask layer or nothing on the other side.
A strip line is an impedance line that separates the upper and lower sides of a line with a ground layer. This type of impedance line is called a strip impedance line, and compared to microstrip lines, signals are less susceptible to interference.
The most common type of controlled impedance in PCB
There are many types of impedance control, and the most commonly used impedance calculation software Polar-Si90 has over 8000 impedances. However, the most commonly used are the following four types and their two variants:
Surface Microstrip
Offset strip line
Edge coupled surface microstrip
Edge coupling offset stripline
The main factors affecting impedance
The impedance value is influenced by PCB material thickness, material dielectric constant (Er) or relative dielectric constant (Dk), conductor width/spacing, conductor thickness, copper thickness, and signal transmission frequency, which are factors that PCB designers need to consider. As a PCB manufacturer, we believe there are 5 factors that can affect impedance values, which are:
Dielectric thickness
Conductor line width/spacing
dielectric constant
Conductor thickness
Solder mask thickness
The relationship between impedance value (Z0) and dielectric thickness (H): the thicker the dielectric, the larger Z0
The relationship between impedance value (Z0) and conductor width (W): the larger the line width, the smaller Z0
Impedance value (Z0) versus dielectric Er (Er): The larger Er, the smaller Z0
Impedance value (Z0) and conductor thickness (T): The thicker the conductor thickness, the smaller Z0
The relationship between impedance value (Z0) and solder mask thickness (T): The thicker the solder mask thickness, the smaller Z0
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