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In this study, the fast-flow, fast-cure, and reworkable underfill materials from two different vendors are considered. Emphasis is placed on the determination of the curing conditions such as temperature and time, and the material properties such as the thermal coefficient of expansion (TCE), storage modulus, loss modulus, glass transition temperature (Tg), and moisture uptake of these underfill materials. Also, the key elements and steps of the solder-bumped flip-chips on low-cost substrates with these underfill materials such as the chip, printed circuit board (PCB), flip chip assembly, and underfill application are presented. Furthermore, the key elements and steps of the rework of the solder-bumped flip-chip assemblies with these underfill materials such as chip removal, chip reballing, substrate cleaning, and new chip placement are discussed. Finally, shear test results of the assemblies with one-time rework and no-rework are presented.