Among many factors that influence the reliability of a flip-chip assembly using NCF interconnections, the most effective parameters are often the coefficient of thermal expansion (CTE), the modulus (E), and the glass transition temperatures (Tg). Of these factors, the effect of Tg on thermal deformation and device reliability is significant; however, it has not been shown clearly what effect Tg has on the reliability of NCF. The Tg of a conventional NCF material is approximately 110°C. In this study, a new high Tg NCF material that has a 140oC Tg is proposed. The thermal behaviors of the conventional and new NCFs between -40oC to 150oC are observed using an optical method. Twyman-Green interferometry and the moiré interferometry method are used to measure the thermal micro-deformations. The Twyman-Green interferometry measurement technique is applied to verify the stress-free state. The stress-free temperatures of the conventional and new Tg NCF materials are approximately 100oC and 120oC respectively. A shear strain at a part of the NCF chip edge is measured by moiré interferometry. Additionally, a method to accurately measure the residual warpage and shear strain at room temperature is proposed. Through the analysis of the relationship between the warpage and the shear strain, the effect of the high-Tg NCF material on the reliability is studied.