Abstract: Against the backdrop of Moore’s Law approaching its limits and the increasing difficulty and cost of next-generation integrated circuit technologies, advanced substrate technology emerges a crucial carrier for supporting I/O enhancementand system integration in the realm of advanced packaging. It is also one of the core components in the post-Moore era. Currently, semi-additive process utilizing build-up film (BF) is one of theprimary methods for achieving fine-pitch multilayer packaging substrates. Given the increasingly prominent issue of signal integrity in electronic equipment operating in high-frequency and high-speed environments, this paper thoroughly discusses the impact of the physical properties of BF material and structural characteristics on signal transmission loss. Based on typical substrate structures, such as microstrip lines and vias, the relationship between BF material parameters and signal transmission performance is studied using an electrical simulation analysis system. It is found that in a microstrip structure, the signal transmission loss increases with an increase in frequency, and this loss is closely related to the dielectric loss factor of BF material. However, in the via structure, the dielectric constant of the BF material significantly influences the equivalent capacitance and the value of impedance, subsequently affecting impedance mismatch. Although the characteristics of the BF material do have some impact on impedance mismatch, the primary factor affecting impedance matching remains the design of via structure itself. In addition, the conductor loss resulting from the skin effect increases with the rise in copper foil roughness at high frequency, offering a crucial reference for quality control of copper foil during the manufacturing process of packaging substrate. This study elucidates the mechanism of physical property and structural characteristics of BF material influencing signal transmission loss, thereby proving a theoretical foundation for the design and optimization of BF material with enhanced physical properties for packaging substrate.