Designed experiment to assess flip-chip-on-board reliability

This paper presents the results of a systematic approach to evaluate the reliability performance of flip chip assemblies on organic substrates using underfill. An experiment involving 11 cells with variations in (a) chip size, (b) substrate thickness, (c) underfill materials, (d) test conditions and (e) passivation layer was designed to optimize the assembly variables and to evaluate reliability performance. The experimental variables were chosen to account for reasonable spread in the strain energies of the assemblies to understand the functional dependence of reliability performance. Failure mode analysis (FMA) suggests delamination of the underfill from the chip surface as the primary failure mode, even though several other failure modes such as chip cracking, substrate cracking, and under-bump-metallurgy defects, were also seen.