The impedance of the circuit board is determined by the physical dimensions (line wide/space) and materials of the circuit and is measured in Ohms (Ω).
PCB impedance control has been one of the essential concerns and challenging problems in high-speed PCB design. As an impedance control designer, you should know what affect PCB impedance and how to calculate impedance.
1.The following parameters largely determine the impedance of a PCB:
1) Distance of signal layer and potential
2) Conductor geometry
3) Trackwidth
4) Copper thickness
5) Permittivity εr
2.Impedance and Delay Calculation Formula of Transmission Lines on PCB
Formula Restrictions:0.1 < w/h < 3.0
Formula Restrictions:0.1 < w/h < 3.0
Formula Restrictions:0.1 < w/h < 3.0
Formula Restrictions:0.1 < s/h < 3.0
Here is some free PCB software that provides impedance control calculations and online calculators as a reference.
Selecting Foil-Built or Core-Built PCBs to Support Impedance Control
PCBHERO Technology normally suggests impedance designers choose Foil-Built PCBs in order to make the most economical PCB. That being said, our Prototype PCB Assembly is very flexible, and we can use Core-Built PCBs. Foil-Built PCBs not only tend to be more economical than Core-Built PCBs, but they are also slightly easier to fabricate. The pictures below explain the differences between the Foil-Built and Core-Built PCBs.
Foil-Built PCB board uses one less core than the Core-Built PCBS in the stack-up. The outside consists of aluminum foil. In addition, foil in different copper weights is much easier to purchase. Since Foil-Built PCBs are made of aluminum, they can be used on any builds, regardless of the primary laminate material used. PP (Pre-pregs) are also less costly than cores, especially if they are 5 mil or thinner.
Core-Built PCB board has cores on the outside, so there is no need to use aluminum foil. Depending on material availability, it may be difficult to acquire a core with uneven copper weights. This forces the PCB manufacturer to etch down the cores, which is costly since a good deal of labor is involved. Except for labor, the PCB factory must use a higher copper weight than what appears on the board, increasing material cost.