Radio Frequency Interconnect Loss Driven by Substrate Dielectric Degradation Mechanisms
Substrate moisture absorption increases dielectric loss tangent, raising RF interconnect insertion loss and reducing long-term wireless link margins.
Microstrip Interconnect
Meaning
Planar signal paths consisting of a single conductor separated from a ground plane by a dielectric layer provide high-speed connectivity in circuit assemblies. Microstrip interconnect structures are fabricated on the outer layers of a printed circuit board for ease of access and component mounting. The signal propagates through the conductor while the ground plane provides the return path for the current.
Because the conductor is exposed, it allows for easy probing during the hardware debugging process.
Propagation Mode
Electromagnetic waves travel in a quasi-TEM mode along the length of the conductor. Part of the energy resides in the substrate and part exists in the air above the microstrip interconnect. This mixed medium causes the signal to travel faster than it would in a completely embedded structure.
Layout Design
Dimensional control of the trace width and the dielectric thickness determines the characteristic impedance of the line. Standard designs target 50 ohms to match the output of common radio frequency components. Surface finishes like gold or tin influence the skin effect losses at high frequencies.
Radiation Loss
Open structures tend to radiate energy into the surrounding environment, potentially causing interference with nearby circuits. Shielding or increased spacing is required when a microstrip interconnect carries high-frequency clock signals or sensitive analog data. Designers limit the length of these traces on the outer layers to minimize EMI emissions and maintain signal integrity.