Reliability of different flex materials in high density flip chip on flex applications

This paper presents the latest results from the reliability tests of high density flip chip on flex application using anisotropically conductive adhesives. Four different types of flexible substrates and two different types of anisotropically conductive adhesives were selected. Both paste and film type anisotropically conductive adhesives were used. Two different test devices were used. The contact areas were 50/spl times/50 /spl mu/m and 50/spl times/90 /spl mu/m. The effective pitch was 80 /spl mu/m in both samples and the number of contacts was 200. The matrix of both anisotropically conductive adhesives was epoxy based and the conductive particles in film type were isolated soft metal-coated polymer particles and in paste type isolated silver particles. The contact resistance was measured with a four-point method and the series resistance with a daisy chain method. The reliability of the flip chip interconnections was tested in thermal cycling tests. Cross section samples were made to analyze the possible failure mechanism of failed contacts.