Macroscale/mesoscale Modeling And Simulation Of Underfill Process

Underfill is an important process in flip-chip encapsulation because of its great impacton the reliability of electronic packagings. Numerical prediction of underfill is beneficialto optimize the encapsulation process and improve the quality of packagings. Existingunderfill molding is mainly two dimensional, and the three dimensional is not satisfied.The mechanism of capillary action in underfill is not well understood. Furthermore, themultiphase phenomenon and particle filler redistribution in underfill could not be analyzedexactly, as the force of complex interface is poorly characterized, the interaction betweenparticles and fluid is not modeled synchronously, and polydispersity of particles could beconsidered. Therefore, it is necessary to employ new methods to describe and analyzethese mesoscale phenomena.In this thesis, we simulate the macroscale and mesoscale process of the underfillencapsulation respectively. In macroscale process simulation, we have done:(1) The driven mechanism of the capillary action in underfill is analyzed bypresenting an inter-motivation model, in which the capillary action is modeled as twodifferent forces, i.e., the unbalanced adhesive force close to the wall and the surfacetension force on the free surface. Those two forces compete and also cooperate with eachother during the capillary flow process, and they are the unity of opposites of the capillaryaction. Based on this model, a layer numerical method for equilibrium state and dynamiccapillary process is established respectively. Parallel-plate experiments and capillary tubeexperiments are conducted to verified our model.(2) Based on the presented inter-motivation capillary model, three dimensional N-Sequation and the Kamal curing reaction equation coupled with generalized Cox-Merzconstitutive model are used to established a macroscale underfill simulation system. ThePSPG (Pressure Stabilizing Petro Galerkin) and SUPG (Streamline Upwind PetrovGalerkin) finite element method is used to solve the equations in our system. In oursimulation, the non-Newton behavior of the melt, curing reaction and thermal responsecould be characterized comprehensively.In mesoscale process simulation, we have done: (3) The modified interparticle-potential LBM (Lattice Boltzmann method) model isused to simulate the mesoscale underfill multiphase flow. The surface tension coefficientof the melt, and its wettability with the surface of die, substrate and solder bumps areanalyzed in the simulation. The effects of the bump bitch, edge channel and encapsulantdispensing are investigated.(4) The Ladd’s LBM model about suspension particles is used to study the distributionof particle filler in underfill process, including the shear-induced migration and the settling.For shear-induced particle migration, the effects of shear rate and particle size areanalyzed. For the particle settling, the particle density, size and viscosity of the melt isinvestigated respectively.