Parametric study for warpage and stress reduction of variable bump types in fcFBGA

The copper pillar with lead-free solder cap bump (Cu w/i LF bump) is found to perform the characteristic of fine pith bump in flip chip technology, lots of dissections for the effects of package geometry and materials are widely investigated in recently years. For the purpose of realizing the mechanical behaviors for the fcFBGA (flip chip fine pitch BGA) with lead-free bump (LF bump), copper pillar without lead-free solder cap bump (Cu w/o LF bump) and Cu w/i LF bump, the three-dimensional finite element analysis (FEA) modeling has been adopted to compare the warpage and stress responses in fcFBGA with these different types of bumps. The simulation results are employed to validate the ICOS experimental results for the fcFBGA. Various parametric discussions for the structural and material effects in fcFBGA such as polyimide (PI) opening size, under bump metallurgy (UBM) size, solder resistant opening (SRO) size as well as Cu pillar height are carried out by using FEA modeling. Because the material properties of underfill and molding compound are usually the key factors to affect the warpage and stresses, for reducing the warpage and stresses in fcFBGA with Cu w/i LF bump, several underfills and molding compounds are selected to study the corresponding mechanical behaviors. The proposed results will be helpful not only for reducing warpage but also for keeping off the critical stresses in fcFBGA with Cu w/i LF bump. It is believed that the results will be useful as the design guidelines if warpage and stress solutions in fcFBGA are required.