Ultrathin silicon chips are becoming more and more popular because of market demand for small, light, and high- performance products with noticeable request of reliability and flexibility. In this paper, the flexibility of the Integrated Circuit package is investigated using finite-element (FE) analysis. ANSYS software is used to analyze a single ultrathin die package in a smart card under four-point bending with the aim of developing flexible smart card modules using chips with thickness below 50 mum. Thicknesses of different layers and Young's modulus of the die adhesive and the encapsulation resin are investigated to find their relative influence on the bending stress field in silicon. The thicknesses of some layers have important influence on bending stress distribution in the module. Decreased copper thickness can reduce considerably the maximal bending stress in silicon die under the same bending condition. As a result, some criteria for the design optimization are given in order to improve the flexibility of the package.