Thermal and Mechanical Loading Effects on the Reliability of COG-ACF with Thin Glass by FEA

The chip on glass (COG) technique has been developed for excellent resolution and high quality liquid crystal display (LCD) panels for several years. In telecommunication field, the glass of LCD with 0.3mm thickness is used in the real product soon. However, many serious manufacturability and reliability issues were observed in the previous studies. In those, warpage of LCD cell is one of the common concerns, for warpage of IC and glass would induce delamination between the interface of gold bump/anisotropic conductive film (ACF) and ACF/glass. The critical parameters of COG process must be closely investigated to achieve minimum warpage. In this paper, based on the finite element analysis (FEA) tool, ABAQUS, we established numerical model of LCD cell, which was verified by warpage measurement system, by taking the detailed interconnect structure into consideration and the equivalent particle method to simulate ACF bonding process and investigate IC warpage under thermal-mechanical loading. We studied heat transfer, critical stress inducing delamination and equivalent particle deformation in the global and local scale. We also explored the effects of bonding force, bonding head temperature and stage temperature on warpage. From the simulation results, warpage are primarily determined by the difference of bonding head temperature and stage temperature