Exposed Die Fan-Out Wafer Level Packaging by Transfer Molding

With continuous development in packaging technology, Fan-Out Wafer Level Packaging (FOWLP) has become an established approach to reach higher integration levels and geometric efficiency. Up to now, the FOWLP market has been mainly focused on compression molding using relative thick mold caps, basically as outcome from the eWLB development started by Infineon. With the wider adoption of FOWLP, also new encapsulation processes and equipment are introduced into the market. One such technology is wafer level transfer molding. This technology progresses on the current FOWLP capabilities, and achieves the thinnest mold cap possible via a process called exposed die molding, which can only be accomplished using transfer molding. This paper discusses two of the key factors that are crucial for a successful transfer molding process of thin 12" exposed wafer level packages. First, the influence of epoxy mold compound (EMC) on warpage is discussed. Contrary to compression molding, transfer molding uses materials which so far tend to induce more warpage. This paper introduces the basics behind warpage and how this can be used to select a proper EMC. Completing this section is an indicative warpage calculation using an analytical approach. Secondly, the topic of dynamic clamping in correlation to exposed die molding is discussed. A key part of exposed die molding is the critical balance between clamping force and the fluid pressure of the injected EMC. The control strategies used to maintain this balance will be discussed in this second section. Finally, an exposed die 12" wafer level molded demonstrator is presented.