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The failure behaviors of flip chip solder joints under various loading conditions of the high-speed shear test (H-SST) were investigated with an experimental and non-linear 3-dimensional finite element modeling study. The solder composition used in this study was Sn-3.0Ag-0.5Cu (in wt.%). The shear forces were far greater by H-SST than by low-speed shear test (L-SST). The shear force further increased with increasing shear speed, mainly due to the high strain-rate sensitivity of the solder alloy. Brittle interfacial fractures were more easily achieved by H-SST, especially at the higher shear speed. This was discussed in terms of the relationship between the strain-rate and work-hardening effect and the resulting stress concentration at the interfacial regions

The adhesion and thermo-mechanical properties of epoxy underfills depend on the epoxy resin, the hardener, and the catalyst. In this study, three different epoxy resins, ERL4221 (cycloaliphatic type), EPON862 (bisphenol F type), and EPON 8281 (bisphenol A type), were cured with 4-methylhexahydrophthalic anhydride (MHHPA) as the hardener using different catalysts: cobalt acetylacetonate (CAA), imidazole derivatives, and tertiary amines. The flow behavior of the epoxy systems was studied with a rheometer. The curing profiles were recorded using a differential scanning calorimeter (DSC), revealing varying catalytic effect for the different catalysts. The curing peak temperature increased in the following order: tertiary amine < imidazole derivatives < cobalt acetylacetonate. The bulk properties of the systems were studied through a thermo-mechanical analyzer (TMA). Epoxy resins cured with different catalysts showed different glass transition temperatures (T_g) and coefficients of thermal expansion (CTE). Among them, the CAA catalyzed systems showed the highest T_g and low CTE. Due to the cycloaliphatic structure of the ERL4221 resin, the cured ERL4221 systems showed the highest T_g compared to the other systems with the same catalysts. EPON8281 systems generally had lower moisture absorption than the other epoxy systems. The surface tension of the underfills was measured. The adhesion strength was evaluated by a die shear test with SiO₂ and Si₃N₄ (SiN) passivated silicon dies as substrates. Although there was no significant difference among the surface tension and contact angles of the underfill materials on the SiO₂ or SiN, there were significant differences in the adhesion. For the ERL4221+MHHPA systems, the CAA catalyzed system exhibited excellent adhesion with SiO₂ and SiN passivation. However, poor adhesion resulted with the catalysis by the imidazole derivatives and the tertiary amines. The bisphenol A and bisphenol F type epoxy resins showed excellent adhesion. Although the CAA catalyzed systems had higher T_g compared to the other systems, their adhesion was worse after aging in a high humidity environment at high temperatures.

The occurrence of flux residue is a manufacturing and reliability concern for flip chip assemblies. In this paper, removal of flux residue by laser cleaning before chip attachment to board is carried out. In the flip chip process, 63%Sn37%Pb solder paste with a water soluble flux was printed on wafer by stencil and subjected to infrared reflow. Instead of washing with water, flux residue on the chips after wafer sawing was removed by ablation of pulsed ultraviolet (UV) lasers with wavelengths of 248 nm and 355 nm respectively. Some parameters in the cleaning process such as the energy density of laser and number of pulses irradiated on the chips had been optimized. It was found that the laser beams also etched polyimide passivation on the chips. After laser etching, the passivation surface became cleaner. The rate of etching was measured by a surface profilometer. To conclude, we discuss the advantages of laser cleaning over wet chemical cleaning in the removal of flux residue.

A 3D model of FCBGA is established, and the thermal-electrical coupling is simulated. The distribution of temperature, current density, temperature gradient, Joule heating under thermal-electrical coupling in solder bump is achieved. Effect of passivation layer opening dimension on electro-migration mechanism is analyzed, and current density evenness is defined to measure the degree of current density unbalance.