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PCB Impedance Influencing Factors

Shenzhen Inno Circuit Co.,Ltd | Updated: Jun 01, 2018

PCB Impedance Influencing Factors

Through the above tests and analysis, the main factors affecting the consistency of PCB impedance and the degree of influence of various factors have been recognized. The main conclusions and suggestions for improvement are as follows:

1. When the line is less than 25 mm away from the edge of the board, the impedance of the line is smaller than the middle of the board by 1~4 ohms. When the distance between the line and the board is more than 50 mm, the impedance value is less affected by the position change. Next, it is recommended to choose the size of the material to be preferential to meet the distance from the impedance line to the edge of the board more than 25 mm;

2. The most important factor influencing the PCB impendence impedance consistency is the uniformity of the thickness at different locations, followed by the line width uniformity;

3. Differences in the residual copper ratio at different positions in the imposition will result in a difference in impedance of 1 to 3 ohm. When the uniformity of pattern distribution is poor (the ratio of residual copper is quite different), it is recommended that a reasonable flow resistance point be laid without affecting the electrical performance. Electroplating diversion points to reduce the difference in thickness and copper thickness difference at different locations;

4. The lower the prepreg is, the lower the glue content is, and the better the uniformity of the thickness after lamination, the smaller the thickness and the larger dielectric constant caused by the flow rate at the edge of the board, resulting in the resistance value of the near-edge line being smaller than the middle area of the imposition. ;

5. For inner-layer circuits, the difference in impedance consistency due to line width and copper thickness at different positions is small; for outer-layer circuits, the difference in copper thickness affects the impedance within 2 ohm, but the etching line caused by the difference in copper thickness The wide difference has a greater impact on the impedance consistency, and it is necessary to improve the copper plating uniformity of the outer layer.