Investigation of Mechanical Stress Distribution in Flexible Microelectronic System Under Bending Force By Finite Element Analysis

Abstract

The emerging demand on flexible microelectronic systems, such as wearable devices, flexible displays, biomedical and heathcare devices, leads to a continuous reduction of the chip thickness. The ultra-thin chips embedded in a flexible substrate would be deformed or fractured by repeated bending, stretching, or twisting under externally applied mechanical stress. Also, the carrier mobilities in the silicon die depend on mechanical stress during operation, resulting in malfunction of the circuitry. To solve these issues of mechanical and electrical reliability, the device layer of flexible system must be located at the “neutral line”, where the mechanical stress is zero. The mechanical stress of package system in rigid substrates was studied extensively, however, the mechanical stress distribution and the position of neutral line of package system in flexible substrates were rarely reported. In the present work, we investigated the mechanical stress distribution in flexible microelectronic system under bending force by finite element analysis (FEA). Both the face-down packaging system using flip-chip bonding process and the face-up packaging system using wire bonding process were considered. Three-dimensional finite element models were constructed using different design parameters, and the static analysis was performed assuming elastic deformations of materials. The stress distribution of each component in the packaging systems, the position of the maximum stress and the neutral line were investigated. The effects of design parameters on the position of the neutral line position and the maximum value of von Mises stress were also discussed. ACKNOWLEDGMENT: This research was supported by “Development of Interconnection System and Process for Flexible Three Dimensional Heterogeneous Devices” funded by MOTIE (Ministry of Trade, Industry and Energy) in Korea Figure 1. The effect of the silicon die thickness on the mechanical stress distribution of the multilayered structure of silicon die/adhesive/polyimide substrate. Figure 1