Hygro-thermo-mechanical Behavior of Adhesive-Based Flexible Chip-on-Flex Packaging

Abstract

Although adhesive-based chip-on-flex (COF) packaging technologies have many advantageous features, such as flexibility and compatibility with standard semiconductor and microelectronics packaging processes, the low hygro-thermal resistance leads to reliability concerns. Thus, finite element (FE) modeling and experimental testing have been used to investigate the effects of temperature and humidity conditions on the hygro-thermo-mechanical behavior of a thin flexible anisotropic conductive adhesive (ACA)-based COF packaging technology. The investigation starts from process modeling of the thermo-mechanical behavior of the technology during the ACA bonding process. The validity of the process modeling is demonstrated by temperature and warpage experiments. Furthermore, three-dimensional (3-D) transient moisture diffusion FE analysis through a thermal–moisture analogy based on the “wetness” technique is performed to evaluate the moisture distribution, in which the moisture properties of the polyimide (PI) substrate are obtained through a moisture absorption experiment. Then, the effect of the moisture properties of the ACA adhesive and PI substrate on the moisture diffusion behavior is examined. Finally, following process modeling, 3-D hygro-thermo-mechanical FE analysis under a constant temperature and humidity condition is undertaken to assess the influence of hygro-thermal aging and stress relaxation of the ACA adhesive on the long-term contact performance of the interconnects.