Analysis of factors affecting impedance control of hard-soft board
The difference in base material has a great impact on the soft board. The resistance value of each material is different, and even if it is the same material, the resistance value of each part will not be exactly the same, just like there are no two identical leaves in the world. kind of truth. The impedance lines on the impedance board generally use base materials with good material stability. If materials with poor stability are used, the material resistance will change greatly. Once the required impedance value is exceeded, the impedance line cannot be used. control lines.
The difference in line width and spacing between impedance lines will cause changes in resistance. Impedance lines are used as resistors, so the width of the line is the size of the resistance value. What does it have to do with absorbing the line spacing? A magnetic field will be generated when the current passes between the lines on the circuit board. The magnetic field can also generate current (generator principle, which is why shielding is required). At this time, the current will change, which indirectly leads to impedance. Control data is inaccurate.
Different material thicknesses cause impedance changes
Electroplating copper tolerance, the impact of this depends on the process flow. In some processes, electroplating occurs before the moment, so it will not affect the impedance at this time. However, when most FPC soft boards are produced, the etched circuits have been completed during electroplating. At this time, copper will also be attached to the impedance circuits, resulting in changes in the resistance of the impedance circuits.
Etching is a kind of corrosion to the circuit, which will affect the thickness and width of the circuit, so we go back to the content mentioned above. Etching can only be maintained within a range, and there are still deviations. These deviations are the cause of resistance changes.