100 μm Pitch flip chip on foil assemblies with adhesive interconnections

In this work the reliability of flip-chip-on-flexible substrate packages with electrically conductive adhesive as first level interconnections is studied. The pitch of the interconnections ranges from 300 to 100 μm with prospects to smaller pitches. The Physics-of-Failure approach is used to determine the nature of such an interconnection and hence the factors that will influence the performance of these packages. The results indicate that moisture is a more important stress factor than temperature. In particular cyclic exposure to high and low moisture levels may lead to degradation of the electrical interconnection. As failure mechanism, reduction of the compressive force that holds the interconnection together is proposed. Further, the proper combination of materials--based on their in- and out-diffusion rates for water--determines the resistance of the packages to reflow-soldering.