Warpage Analysis and Prediction of the Advanced Fan-Out Technology Based on Process Mechanics

Abstract

Moore’s law has remarkably promoted the development of semiconductor technology over the last decades. The advanced packaging involving novel materials, structures, and processes has contributed significantly to achieving excellent performance. Among various forms of advanced packaging, wafer-level-fan-out packaging is superior to standard wafer-level packaging in that it allows more input/output (I/O) connections, leading to landmark development for high-end devices. Furthermore, fan-out wafer-level package (FOWLP) technology enables heterogeneous integration of chiplets fabricated with different manufacturing processes, which provides integrated, sophisticated, and multifunctional dies with higher performance, lower cost, and tinier size. In packaging materials, processes, and structures, a thorough understanding of the process mechanics is necessary to ensure accuracy, while multiphysical field and multiscale modeling are beneficial to clarifying the internal mechanism of warpage. Process mechanics was applied to FOWLP and the characteristics were systematically expounded. Focusing on the warpage analysis of the embedded silicon fan-out (FO) wafer-level package, we introduced the principle of process mechanics and explored the material–structure–process interaction. The typical processes (including: 1) cleaning and litho cavity; 2) die attach and assignment; 3) dry film and dielectric layer 1 and patterning; 4) physical vapor deposition (PVD) seed layer 1 and patterning copper plating and redistribution layer (RDL) 1; 5) dielectric layer 2 and patterning; 6) PVD seed layer 2 and patterning copper plating and RDL 2; and 7) passivation layer, drop ball back grinding, and dicing) of the embedded silicon FO packaging are analyzed in detail to explore the warping evolution of individual processes. In addition, a material equivalent model of representative volume element (RVE) and an extended theoretical model of a multilayer structure were proposed. The comprehensive comparison for the extended theoretical model, experimental measurement, and finite element model (FEM) showed that the theoretical model is effective and relatively accurate. Overall, both the theoretical model and FEM are feasible approaches for predicting the warpage during the manufacturing process.