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This paper gives an overview of flexible base and joining materials, focusing on their applications and environmental specifications such as applicable temperature and humidity ranges. Mechanical (peel, shear, tear strength) and environmental (moisture absorption, dimensional stability, delamination) tests have been done on the most widely used base film materials (PI, PEN and PET) to determine the influence of processing temperatures on their properties. Three different test boards for mechanical tests, assembly evaluation and reliability tests were designed, built, assembled and evaluated. The joining materials applied for the test structures include traditional SnPb, lead-free and low temperature lead-free solders and different conductive adhesives. This wide range of base and joining materials facilitates their comparison from the reliability point of view.