In relation to standard injection molding the challenges of testing methods, increasing complexity as well as the process and equipment requirements of micro injection molding will be discussed. The mechanical behavior of micro injection molded specimens was investigated. Therefore, a new tensile test specimen was developed to evaluate systematically the impact of interfaces (e.g. weld lines/ multi material interfaces) on small scale applications. A failure observation of micro injection molded specimen was carried out under a light microscope. The processing effects on spherulitic structure were linked to bonding strength, material properties and injection molding simulation.