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Investigation and Methods Using Various Release and Thermoplastic Bonding Materials to Reduce Die Shift and Wafer Warpage for eWLB Chip-First Processes

Evaluating various factors used in a die attach process for chip-first FOWLP.

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Today’s fan-out wafer-level packaging (FOWLP) processes use organic substrates composed of epoxy mold compound (EMC) created using a thermal compression process. EMC wafers are a cost-effective way to achieve lower profile packages without using an inorganic substrate to produce chip packages that are thinner and faster without the need for interposers or through-silicon-vias (TSVs). One approach using embedded die technology (eWLB) for FOWLP is a chip-first (mold-first) die assembly in a face-down configuration on an intermediate carrier wafer. The ideal chip attachment scheme should minimize lateral movement of the die during over-mold (die shift) and also minimize vertical deformation of the bonding material which results in die protrusion (stand-off). An ideal die attach material should provide adequate adhesion to the EMC wafers without inducing excessive substrate warp, while permitting a suitable debonding process, including complete residue removal. The attachment scheme must also survive any thermal, mechanical, and chemical processes that are performed prior to carrier release. The bonding materials must also have sufficient adhesion to the EMC material to overcome such stress without bond failure. Preventing lateral die shift and deformation due to the coefficient of thermal expansion (CTE) mismatch between the carrier substrate and EMC material can be accomplished using an appropriate bonding material. Using a chip-first die attach process, this investigation will address die shift and deformation using various release and thermoplastic bonding materials. Combinations using different EMC products and carriers with various coefficient of thermal expansion (CTE) are also included. Successful pairs will then undergo carrier release using either mechanical release or laser ablation release technology.

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