1. The line width should be wide rather than thin.
Because the limit of fine found in process, wide is no limit, so in order to later if the impedance of the line width adjustable fine and run into a limit that trouble, or increase the cost, or relax impedance control. Therefore, the relative width in the calculation means that the target impedance is slightly lower, such as the single line impedance of 50ohm, we can calculate to 49ohm, and try not to calculate it to 51ohm.
2. Overall present a trend.
In our design, there may be multiple impedance control targets, so that the whole is large or small, and do not appear to be larger than 100ohm, and the deviation of 90ohm is small.
3. Consider the residual copper rate and the flow glue quantity.
When half a piece of one side or both sides is etched lines, curing bonding glue to fill in the process of etching, the gap between the two layers of this adhesive thickness time will decrease and the residual rate of copper is smaller, the more complete, the less the rest. Therefore, if the thickness of the two-layer semi-solidified film is 5mil, select a slightly thicker semi-solidified film according to the residual copper ratio.
4. Specify the glass fabric and the amount of glue.
Different glass cloth, different rubber content of curing or core board of dielectric coefficient is different, even the same height could be the difference between 3.5 and 4, this difference can cause single about 3 ohm impedance change. Another window size is closely related to the effect of glass fiber and glass cloth, if is 10 GBPS or more the design of high speed, and laminated materials not specified with the leaflet 1080 material plate factory, the signal integrity problems may appear.
of course, the residual copper rate of resin flow calculation, the dielectric coefficient of new materials and nominal inconsistent, sometimes some glass cloth plate factory without preparation, and so on can create design of laminated implementation or delivery delay. So the best way to do that is to make the plate factory at the beginning of the design, and add their experience to design the laminate, so that at most a few of the back and forth can get the ideal and achievable lamination.