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2.5D multichip module packaging technology for higher end devices like CPU, GPU, 3D NAND flash memory and High Bandwidth Memory (HBM) require two major molding process solutions: higher thermal performance and narrow gap underfill. Apic Yamada Corporation of Japan, as a semiconductor back end total solution provider, proposes technology solutions utilizing advanced molding technologies which enable chip surface exposure and Mold Underfill (MUF) for narrow gaps.With conventional molding technology, the mold resin on the top surface of the chip is removed by a grinding process after the molding process in order to improve thermal resistance θja. However, the latest transfer molding technology enables chip exposure without a grinding process. This technology can be applied to a wide range of higher end advanced packaging technologies such as 2.5D, 3D and others. The conventional chip exposure molding method using elastic release film, which covers the inside of the mold cavity, can absorb chip height variations. In addition, the most advanced available chip exposure molding system applies reduced pressure and lower mechanical stress to the chip. This low stress molding process comprises several new system technologies including chip height measurement using a laser displacement sensor, which is self-calculating to provide the optimum cavity level for chip exposure, by adjusting the cavity block position each cycle.In this study, solutions for chip height variation such as +/- 20um and height control range within 300um with low stress will be presented. In addition, we propose newly developed vacuum molding technology and movable air vent technology for MUF with void less filling of narrow gap spaces under the chips. Proper mold resin material selection to achieve high filling, optimal heat shrinkage and minimized warpage is one of the key factors. The new technology also provides economic advantages due to reduced process steps and shorter process time compared to the Capillary Underfill (CUF) process which is widely used in the marketplace.In order to achieve a reliable MUF process targeting less than 8um gaps and less than 15um pitch, Apic Yamada’s molding system has tighter control for discharging internal air and generated gas to the outside. This is accomplished while also controlling vacuum conditions, using chip volume measurement by laser displacement sensor and 3D image measurement which calculates the resin flow front on each shot. |
