Coated microstrip

In the microstrip configuration, the signal conductor is surrounded by air (except on the dielectric surface). If the conductor is coated by another dielectric, such as a glaze or encapsulant, it is referred to as embedded or coated microstrip. If the dielectric constant of the coating is close to that of the supporting dielectric, the impedance of the line will be lowered by 10-20%, and the signal propagation delay will be increased by about 20%. 

Recent developments of the collaborators from Coimbra [34,35] permit the detection of the secondary scintillation light using a Microstrip Gas Chamber (MSGC). The UV photons are detected by Csl-coated thin-film photocathodes deposited directly onto a microstrip plate (MSP). A system has been developed where a thin quartz window separates the xenon GPSC from the MSGC, filled with P10 (Ar + 10% CH4) gas or xenon gas. A schematic view of the operation is shown in Fig. 9. 

Since the coating is a dielectric material, it changes the impedance of high-speed traces on the surface of the PWB. Boards with microstrip are usually not coated for this reason. Radio frequency (RF) PWBs for severe environments can still be coated if the traces are buried microstrip or stripline, which are unaffected by the additional coating on the board surface. 

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