Results of a high density flip chip on flex reliability test program

This paper presents results from an extensive reliability test program on high-density flip chip assemblies on flexible substrates. The test program included thermal cycling, high temperature, hot humidity and pressure cooker tests. In this reliability test, four different kinds of substrates were used: polyimide, polyester and epoxy glass with 80 μm pitch and upilex with 54 μm pitch. Two different layouts of the bond pads were designed, peripheral and staggered, and chip and flex were assembled using thermosetting anisotropic conductive adhesive film. The test samples were measured electrically using a four-point method for the contact resistance and a daisy chain for the overall yield of the contacts. Afterwards cross sections were made to determine the reason of the failures. This work was carried out in the frame of the European Union funded IST project "FLEXIL".