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Managing the Underfill Process in Transient Thermal Environments

In the world of microelectronic assembly most process developments are aimed at making smaller components to fit more functions into ever smaller portable devices. This study was designed to look at large device underfill, where the silicon die is over 15mm on a side, and the amount of underfill required is on the order of 30 to 50 mg. The manufacturing process for these large die are pushing throughput requirements to much higher levels than seen on production lines today, bringing new challenges to dispensing underfill.
When such large devices are produced at rates over 3000 uph the dispensing tools have to move a lot of material. The sheer volume of material passing through the jet may present problems in heating fluids to the desired process temperatures before dispensing. This impacts the accuracy of shot size because underfill fluids change viscosity with changes in temperature, and for a given cycle, jet the shot volume can change slightly. This in turn impacts material keep-out zones next to the die. Constant temperature of the underfill fluids results in greater repeatability of shot size, aids flow under the die, and improves fluid break off. During this study, it was also observed that the system thermal environment (inside the dispensing machine) had a large impact on the shot weight dispensed.

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