PCB Impedance Calculator - Embedded Microstrip Impedance Calculation
Embedded microstrip is similar in structure to microstrip transmission lines. Modeling approximations can be used to design embedded microstrip transmission lines. By understanding embedded microstrip transmission lines, designers can properly build these structures to meet their needs.
An embedded microstrip line consists of a flat conductor suspended over a ground plane. The conductor and the ground plane are separated by a dielectric. There is also a layer of dielectric material over the conductor. One case of an embedded microstrip transmission line is a microstrip trace with a solder mask.
Embedded Microstrip Transmission Line Models
Eq. 1 Models have been created to approximate the characteristics of the embedded microstrip transmission line. A good approximation is provided by the formulas contained in the document IPC-2141A [1]. For an embedded (internal) microstrip, the formulas provided in paragraph 4.2.3 shall be used. The characteristic impedance is given by:
where Z0,surf can be computed as specified in Eq. 1 of the Microstrip Calculator using H2 in place of h, εr,eff can be computed as specified in Eq. 2 of the Microstrip Calculator, h=H1 and b=H2-H1.