Influencing factors of characteristic impedance of pcb circuit board
1. When the route is less than 25mm from the edge of the board, the characteristic impedance value of the route is 1~4ohm smaller than that in the middle of the board, and when the distance from the route to the edge of the board exceeds 50 mm, the characteristic impedance value is less affected by the position. Under the premise of high efficiency, it is suggested to select the material cutting specification first considering that the distance between the characteristic impedance line and the edge of the plate exceeds 25mm;
2. The most important factor affecting the uniformity of the characteristic impedance of the pcb circuit board is the thickness uniformity of different parts, followed by the uniformity of the graphic boundary;
3. The difference in the residual copper rate of different parts of the pcb circuit board will lead to a difference of 1~4ohm in the characteristic impedance. Basically effectively pave the separation point of the flow blocking image and the electroplating process to reduce the difference in the thickness of the different parts and the difference in the thickness of the barrel plating;
4 The lower the clamping force of the semi-dry solid sheet, the better the uniformity of the dielectric thickness after lamination. The exchange of glue flow at the edge of the pcb circuit board will cause the dielectric thickness to be too small and the relative permittivity to be too large, which in turn will lead to close-to-the-board The characteristic impedance value of the edge route is lower than the middle area of the panel;
5 For the inner layer route, the difference in the uniformity of characteristic impedance caused by the graphic boundary and copper thickness in different parts of the jigsaw board is small. For the surface layer route, the impact of copper thickness difference on characteristic impedance is within 20hm, but the etching caused by copper thickness difference The difference in the boundary of the process pattern has a great impact on the uniformity of the characteristic impedance, and it is necessary to improve the uniformity of the surface barrel plating.
