Thermal interface materials (TIMs) are an important component in electronic packaging, and there is a concerted effort to understand their reliability when used under various environmental load conditions. Previous researchers have investigated gap fillers and other types of TIMs to understand their performance degradation under loading conditions such as thermal cycling and thermal aging. Most of the study in the literature focuses on studying the changes in thermal properties, and there is a lack of understanding when it comes to studying the mechanical behavior of TIMs. Degradation of mechanical properties is the cause for the loss in thermal performance and is critical during TIM selection process. Moreover, mechanical properties such as modulus and coefficient of thermal expansion (CTE) are critical to assess performance of TIMs using finite element analysis (FEA) and potentially save time and money in the evaluation and selection process. Due to the very soft nature of TIMs, sample preparation is a challenging part of material characterization. In this paper, commercially available TIMs are studied using testing methods such as thermomechanical analyzer (TMA), dynamic mechanical analyzer (DMA), and Fourier infrared spectroscopy (FTIR). These methods are used to characterize the material properties and study the changes in properties due to aging. In this work, the followings are presented: impact of filler content on the mechanical properties, sample preparation method for curable TIM materials with specified thicknesses, and impact of thermal aging on mechanical properties.