This paper presents a methodology to determine the durability of Quad Flat No-Lead (QFN) package. The QFN package is useful for improving the reliability of the package. A mechanical fatigue test namely three points bending cyclic test and signal analysis were proposed in this paper. The three points bending cyclic test method is a test assembly that supports a specimen on two anvils or rollers, and symmetrically loads the specimen on the opposite surface with an anvil or roller using micro-tester machine. For strain signal collection, a strain gauge was connected to the dynamic data acquisition system, and it was used for each tested QFN package for determining the response of the captured cyclic strain signal. It was found that the sinusoidal amplitude pattern of signal response has been obtained during the constant three points bending cyclic test. The obtained response signals were then analysed using the Power Spectral Density.