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May 15th, 2012
Molding Technologies: a closer look
At the recent IMAPS Micro/Nano-Electronics Packaging & Assembly, Design and Manufacturing Forum (MiNaPAD) in Grenoble, in late April, Rolf Aschenbrenner of Fraunhofer IZM gave a detailed presentation on molding technologies for system integration. I-Micronews thought it was worth “A Closer Look”.
Typical encapsulation technologies include: glob top, underfilling, transfer molding and compression molding.
Newer Epoxy molding compounds have been developed which can simultaneously underfill and overmold the Flip Chip die in a single transfer molding process. With suitable mold design, such MUF technology (molded underfill) can utilize the currently installed capital base. The ability to apply pressure during the molding process can reduce the void rate under the die as well as achieving production efficiencies which are typical of transfer molding processes. Molded underfill compounds offer enhancements in thermal expansion coefficients and moisture absorption levels relative to traditional liquid underfills as well as low levels of package deformation due to cure shrinkage and thermal mismatch effects. These improvements are achieved through the use of proper resin chemistries and filler package compositions. Such solutions are, however, limited in terms of gap (ball size) and pitch that they are capable of. For further details on MUF capabilities see ref 1.
Compression molding is a forming process in which the epoxy molding compound is placed directly into a heated mold cavity, is softened by the heat, and forced to conform to the shape of the mold as the mold closes. Compression molding has recently come into vogue for so called “fan out packaging” , i.e the molded reconfigured wafers of Infineon  and their licensees and the redistributed chip package of Freescale .
The basic steps towards a molded reconfigured wafer are: a) relocation, b) fixture at a new location, and c) encapsulation to fill the gaps between fixed chips and to cover the backside. As shown in the figure below, 1) tape is laminated to a carrier plate ; 2) the die are placed onto the mounted tape face down; 3) the mounted chips are encapsulated by compression molding using a liquid molding compound; 4) the molded wafer is released from the carrier plate and the tape is pealed from the molded wafer. The molded wafer is then processed with RDL, balling and singulation.
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