To lower the manufacturing cost of quad flat no-lead (QFN) packages, the number of QFN packages on a leadframe must be increased. However, the increased number of packages or changes to the layout of QFN packages on the leadframe can impact the mold compound flow behavior, which will, in turn, affect warpage, and the generation of voids inside the mold compound. In this paper, both simulation and experimental approaches were conducted to study the behaviors of QFN packages on a leadframe strip. For simulation, we will demonstrate and present an analysis methodology to account for the in-line processing parameters, especially the step of manufacturing and processing the mold compound material to form the QFN packages on a leadframe strip. The in-line manufacturing parameters, such as pressure, temperature, shrinkage, and processing timing, were all considered and modeled. A commercial finite element tool was used. For the experiment, we measured the warpages and the voids of QFN packages as a function of the package location on the leadframe. The warpage of the package, and the voids generation of QFN packages at different locations on the leadframe strip were studied. In conclusion, the experiment vs. modeling data was correlated, and the study proved to be very useful for the prediction of warpage, and void generations.
In this paper, the thermal performance data of theta jc (Rth-JC) and theta ja (Rth-JA) of a flip chip ball grid array device with heat spreader, fcBGA-H, is measured. For Rth-JC, various boundary conditions for the thermal resistance modeling are considered and discussed. A transient measurement method is used to obtain the temperature responses of the diodes, as a function of time. The structure functions of the diodes are measured, and based on the structure functions, the thermal resistances are calculated. With the structure functions, the impact of package configurations are better viewed and demonstrated, and a novice measurement technique is also proposed here to measure the thermal resistance of junction to die, Rth-JD. With this experimental setup, there is no need to use the thermal couples. The traditional drilling hole for thermal couple and thermal couple itself will change the package configuration and heat dissipation path, and, therefore, impact the accuracy of the measurements.
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