| Summary: | 碩士 === 國立臺灣大學 === 機械工程學研究所 === 87 === Currently, most flip chip are encapsulated by dispensing the encapsulant along the partial periphery of the chip. The encapsulant is driven by capillary force flows through the space between the chip and the substrate (board). The filling time is the major problem of the production. Sometimes the underfill process generates voids via the inappropriate dispensing method. As the chip's number of I/O increase, the traditonal analysis by assuming the flow between two plates will be inaccurate. The pressurized underfill can conquer the slow production problem,but there is voids generated problem.
This study put emphasis on underfill through the high bump density space.By observing the flow via the transparent model, analyzing the filling time and voids by different dispensing methods. The study also analyzes the flow affected by bumps. By deriving the mathematics model, we can calculate the filling time and melt front distance by computer programs. The study also simulates the pressurized underfill process. We change the mold geometry to analyze the change of flow.
Appropriately extends the dispensing route from periphery of one side or two sides of the chip, can reduce the filling times. The encapsulant contact the bumps can increase the flow speed. When the melt front flows through the half of the bump, the flow velocity will be much slower than before the melt front through the half of bump. In pressurized underfill simulation, the study finds that the side region of the mold(fillet) is dominate the flow pattern. It's unfruitful to add dam in the fillet space to prevent the encapsulant from flowing in the fillet. Using the mold geometry properly can avoid void generation and reduce the maximum necessary pressure.
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