In-process Warpage Prediction and Optimization for Heterogeneously Integrated Packages Using a Novel Thermo-mechanical Modeling Scheme

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Modern-day semiconductor packages have been focusing on heterogeneous integration of chiplets to enable multiple functionalities, improve device performance and reduce manufacturing cost. A class of heterogeneous integration schemes involves reconstitution of known good dies using epoxy mold compound (EMC) and formation of redistribution layers (RDLs) to fanout electrical connections from the chips to a larger pitch compatible with that of the substrate pads. Typically, this reconstitution and RDL processing are performed at wafer-level. Subsequently, the reconstituted wafer is diced to singulate the molded chip-modules which are then assembled onto the substrates. Depending upon the physical properties of different materials involved in the fabrication process, their relative proportions and processing temperatures, the wafer-level warpage during the process can become very high and fluctuate between the convex and concave shapes. This could make the fabrication process and wafer handling very challenging. Hence, it is important to control the in-process wafer warpage. Here, we develop a novel thermo-mechanical modeling scheme utilizing the finite element method that can predict (i) the evolution of the wafer-level warpage during the fabrication process, (ii) warpage of the singulated chip-module, and (iii) warpage evolution during the package assembly process. The model incorporates effects of large deformation, material addition or removal during the fabrication process, and chemical shrinkage of polymer materials. For a typical multi-die molded packaging process, we analyze using this model, effects of (i) mold to silicon area ratio, (ii) number of dies and spacing between them, (iii) number of RDLs, (iv) properties of temporary carrier, and (v) properties of EMC material on wafer-level in-process warpage and package warpage. Subsequently, we propose optimal values of material and process parameters that reduce the warpage. The modeling approach presented in this work will help optimize package fabrication and assembly processes without having to build multiple legs of a test vehicle.