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Compression Molding for Thin PoP Top Packages
Keywords: Compression Molding, Package on Package (POP), stacked Die
Package on Package configuration is gaining popularity as it allows flexibility in design and manufacturing. Top memory package is being challenged to reducing the package thickness but also keep higher die stack up. One way to accomplish thinner package is using the thinner substrate i.e, reducing substrate thickness ~100um and thinning the die to 50um and below. Reducing the mold cap can also be considered as one option. At present transfer molding remains dominant molding method for thin PoP packages. However, yield is impacted by interactions with mold cap clearance and wire density limiting transfer mold application to thin package manufacturing. Compression molding is used for the first time to manufacture thin POP packages to overcome these transfer mold interactions. We report manufacturing process flow and material selection for the compression mold. Key objective for study is to reduce mold cap clearance (distance between the die top to mold top) to sub 100um and study the package warpage at ambient and reflow temperatures. As part of the experiments, packages molded by transfer mold with pellet form factor were compared to compression mold with powder and granular form factor. Results indicate that there is considerable difference in warpage behavior between pellet and powder form of same mold compound. However, the granular form of the same mold compound resulted in similar warpage behavior of pellet form mold compound. Further analysis was done to compare the filler distribution in the mold for transfer Vs compression mold process. Results indicate much uniform filler distribution in compression mold further evidence that the warpage for unit level package will be uniform across the strip. Wire sweep data will be presented for the compression mold results. Warpage results were analyzed using Finite element methods, and further the results are extrapolated to different package XY dimensions. The data obtained from these experiments show that compression mold method can be successfully implemented for thin POP Top packages in the future.
Ravikumar Adimula, Sr. Packaging Engineer
Mesa, AZ

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