I need to set up a differential pair of traces on a PCB for 90 ohms. I cannot find what values for epsilon I should use on the stackup page for FR4. In fact, I cannot find the epsilon value anywhere. I'm creating a 4 layer 1.6mm 1oz board and need to tune my traces for a differential pair. KiCad requires the Epsilon R and Loss Tangent values. It also asks for the values and type of mask.
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