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This paper presents the results from the evaluation of different types of flexible substrates for high‐density flip chip application. In this work two different types of base materials were used, epoxiglass (EG) and polyimide (PI). According to previous tests the type of conductive particles in the adhesive seems to be one of the key factors in high‐density interconnections. The adhesive selected for these tests was a composite of epoxy matrix and high content of isolated soft metal‐coated polymer particles. Two different test structures with contact areas of 50 × 50μm and 50 × 90μm were compared. The total amount of contacts in one IC was approximately 200 and the effective pitch size was 80μm. The contact resistances were measured by four‐point method and the continuity by daisy chain structure. The reliability of the flip chip interconnections was tested in thermal cycling and humidity tests.