The reliability problem of thin/ultra-thin die used in IC card becomes the most primary problem which restrains the further application of IC cards. Failure induced by die crack takes over 50% of all failure modes. This paper paid attention to the crack mechanism of thin/ultra-thin die crack problem, especially emphasized on the crack due to mounting process. During the mounting process, the instant pressure made by thimble can reach GPa level, which easily results in the imprint damage. The sliding contact between thimble and die could leave the scuff mark on the die. Photos were taken to describe the figure and size of two kinds of micro damage. LEFM approach was used to analyze the effect of different kinds of damage. According to the results of quantized analysis, the micro damage appeared during mounting process could significantly decrease the intension of die, which finally make the die easy to crack. Packaging process could also bring extra stress to the thin/ultra thin die, which is often neglected during the process because its damage on reliability may not work immediately. Through the temperature circle and mechanical distortion in the daily life, the stress can finally make the die crack and impact the lifetime of the IC smart card. Several methods are put forward to deal with the aforementioned problems, protect the die from crack issues and increase the yield of ultra-thin IC smart card module.