Requirements and Suggestions on Impedance Matching in Four Layer PCB Design

Suggestions on lamination and impedance calculation and adjustment of a four layer PCB

Recently, a four layer PCB was designed. Because it is a high-speed circuit and has impedance matching requirements, it specifies which lines to make impedance lines when sending it to the PCB Factory for proofing. My own requirements for making boards are as follows.

The lines with impedance matching requirements include single ended 50 ohm RF line, 90 ohm USB differential line and 100 ohm DDR differential line, as shown in the figure below,

50 ohm RF line impedance requirements:

90 ohm USB differential line and 100 ohm DDR differential line impedance requirements:

I have simply calculated the impedance of the above impedance line. The semi cured sheet is 2116, the height of the reference plane is 4.5mil, the dielectric coefficient is 4.2, and the copper thickness is 1zo. The line width of single ended RF line is 6mil and the spacing is 10mil. The impedance of single ended RF line is 50.47 ohm.

The line width of USB differential line is 5MIL, the spacing is 5MIL, and the line to ground spacing is 6mil. The calculated result is 88.96 ohms.

The lamination and impedance calculation adjustment suggestions fed back after the board factory evaluation are as follows,

According to the information fed back from the board factory, the core thickness used by the board factory is 1.3mm, and the semi cured sheet is

3313pp, the thickness is 0.1mm, which should be about 4mil in mil.

The 50 ohm single ended RF line does not need to be adjusted. The impedance calculated according to the lamination method of the board factory is 51.77 ohm, which can meet the impedance requirements

The 90 ohm USB differential line needs to be adjusted from the original 5MIL linewidth and 5MIL spacing to 5.5mil linewidth and 4.5mil spacing. The calculated impedance is 89.89 ohm to meet the requirements.

The 100 ohm DDR differential line does not need to be adjusted. The impedance calculated according to the lamination method of the board factory is 99.42 ohm, which meets the requirements.

Editing: hfy

Requirements and Suggestions on Impedance Matching in Four Layer PCB Design 1

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