Some processing requirements for multilayer characteristic impedance plates
The calculation method of the impedance value is generally like this: 8.0 (98.5ln41.1 / 870TWHZr), the layer is different, the type is different, the specific formula used by their impedance is different, but the main factor affecting the characteristic impedance value Have:
Dielectric constant: The dielectric constant of FR-4 material is generally between 4.5 and 4.9, depending on the material used for processing the circuit board. The manufacturer's calculation generally uses 4.5.
Dielectric thickness: refers to the dielectric thickness between the signal layer that controls the impedance value and the specified reference layer.
Lead width and lead spacing: For single-ended impedance lines, only the layer and line need to be specified for impedance control. In addition to the first two parameters, differential impedance lines must also indicate the fixed distance between the two signal lines. ;
Wire thickness: depends on whether the control impedance line belongs to the inner layer or the outer layer
1 Relative to the inner layer: when the minimum line width and minimum distance> 5mil, the thickness of the finished copper foil of the inner circuit: 33μm; when the minimum line width and minimum distance ≤ 5mil, the thickness of the finished copper foil of the inner circuit: 15μm;
2 Relative to the outer layer: When the minimum line width is ≥10mil and the minimum distance is ≥8mil, the thickness of the copper foil of the finished circuit is: 70μm; when the minimum line width is <10mil and the minimum distance is <8mil, the copper foil thickness of the finished circuit is: 40 μm.