Contactless smart cards are widely used in various applications, such as access control, transit fare payment systems, etc. In order to improve the performance and at the same time to reduce the production costs, research effort on the application of new materials and the development of new processes continues. In this study, the assembly process of contactless smart cards using a film-type non-conductive adhesive (NCA) was investigated and modified taking into account the limited heat resistance of the poly(ethylene terephthalate) substrate used in the tests. Pressure cooker tests were then performed to further evaluate the reliability performance of the adhesive joints in high temperature and high humidity conditions. The assemblies underwent both mechanical and electrical characterizations after the assembly process, as well as during and after the reliability tests. Examination of surface morphologies and cross-sections by scanning electron microscopy and optical microscopy was conducted to establish the failure mechanism.