Detailed study of material compatibility of the various electronics packaging materials for immersion cooling is essential to understand their failure modes and reliability. The modulus and thermal expansion are critical material properties for electronics mechanical design. Substrate is a critical component of electronic package and heavily influences failure mechanism and reliability of electronics both at the package and board level. This study mainly focuses on two major challenges. The first part of the study focuses on the impact of thermal aging in dielectric fluid for single-phase immersion cooling on the non-halogenate substrate’s thermo-mechanical properties. The second part of the study is the impact of thermal aging on thermo-mechanical properties of substrate in the air. The non-halogenated low Coefficient of Thermal Expansion (CTE) bismaleimide triazine (BT) resin laminate is used for its ultra-low CTE which in turn reduce the warpage of substrate. Moreover, the substrate has high glass transition temperature and high stiffness suitable for the application which requires high heat resistance. The substrate is aged in ElectroCool EC100 dielectric fluid, and air for 720 hours at three different temperatures: 22°C, 50°C, and 75°C. The complex modulus is characterized before and after aging for both parts and compared.