Experimental and numerical reliability investigations of FCOBassemblies with process-induced defects

摘要

To develop comprehensive design guidelines, models and experimentscannot overlook process-induced imperfections in the flip chip on board(FCOB) assemblies. The following items were noted as being significantfactors which were used for modeling and by thermal cycling tests: (a)varying standoff-heights and alternative bump sizes, (b)underfill-particle settling, (c) underfill-void effects, (d)underfill-to-bump coverage, (e) asymmetrical fillets vs. symmetricalfillets. A detailed numerical and experimental reliability study ofperfect and imperfect flip chip assemblies has been completed.Experimental studies of the failure modes and of the mean cycles tofailure are in good agreement with the failure modes and life time, aspredicted by FEM for the different technological variants. A hierarchyof influences was worked out in three levels (important, medium,negligible). Most important imperfections resulting in a strongreliability decrease are particle settling, asymmetrical fillets andsmall and big voids