Electromagnetic-Thermal Coupling Modeling and Analysis of High-Speed Transmission Line on LTCC Substrate in SiP

With the growing simultaneous demands for miniaturization and high performance, thermal issues such as hotspots severely degrade the high-speed signal transmission performance of low temperature co-fired ceramic (LTCC) substrate in system-in-package (SiP) modules. This paper proposes a high-speed transmission line design for LTCC substrates, using a G-S (Ground-Signal) structure to ensure reliable signal transmission quality. Based on this structure, finite element simulations are performed to investigate the electromagnetic signal transmission characteristics under both uniform and non-uniform thermal fields, confirming that signal transmission efficiency exhibits strong temperature dependence. The results indicate that when the temperature exceeds 50 °C, non-uniform temperature distributions exert a significantly stronger influence on electromagnetic performance, leading to aggravated signal reflections and reduced transmission efficiency. At 300 °C, the transmission efficiency under non-uniform temperature drops to 35.0%, which is a 61.8% decrease compared with the optimal scheme obtained under ideal electric field conditions. Under electromagnetic-thermal coupling, a comparative study of different schemes shows that the optimal design derived from a single electric field is not suitable for electromagnetic-thermal coupled working conditions. The optimized Scheme 2 increases transmission efficiency to about 75.3%, with smoother S-parameter curves and smaller fluctuations. These findings provide valuable references for subsequent reliability-oriented design and experimental verification.