IFTLE 20 ASE Examines Materials and Process Changes for Advanced WLP
Initial WLP products manufactured under the FCT UltraCSP license (i.e Amkor, ASE, SPIL, STATSChipPAC, National, etc. )used BCB dielectric, Ti/Al/Ti RDL and Al/NiV/Cu UBM. Larger chips and more difficult reliability requirements have seen a shift to PI and PBO type dielectrics which have higher elongation and are considered “tougher”, a shift to Cu RDL and a shift away from sputtered Al/NiV/Cu UBM.
At the recent IEEE ESTC (Electronic System-integration Technology Conference) in Munich, John Hunt of ASE detailed dielectric, RDL and UBM change options for their WLP technology.
Hunt concludes that in both the temp cycling and drop test results, cell 8 shows the highest first fail and Weibul 63.2% cycle to failure data. Cell 5 would rank 2nd. Overall both cells have 7.5 um of dielectric in both the first and second RDL layers . Cell 5 uses PI and performs slightly better in the temp cycle tests and cell 8 which uses PBO performs better in the drop test.
All cells with 5 um dielectric performed poorly. Al/NiV/Cu sputtered UBM performed poorly. PBO 2 (lower cure temp – 250 C) performed better in TCT than in drop test. Higher elongation, lower modulus PBO 1 gives better drop test results.
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