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The flip-chip on organic substrate has relied on underfill to enhance the solder joint reliability. The invention of the wafer level underfill technology has greatly improved the production efficiency of the flip-chip process. The development of wafer level underfill materials and processes relies on the fundamental understanding of the underfill curing process. A wafer level underfill material is developed; its curing kinetics is modeled using an autocatalytic model, based on which the B-stage feasibility of the underfill is investigated. The B-stage properties of the underfill are characterized in terms of its Tg, hardness, adhesion, dicing and storage capability. The developed wafer level underfill displays the high curing latency required in the reflow process, as well as good mechanical properties after the B-stage. The underfill is applied on a 6 inch bumped wafer and B-staged. Then the wafer is diced into individual components and assembled onto the FR-4 board.