| Summary: | 碩士 === 國立交通大學 === 材料科學與工程系所 === 97 === Light leakage Mura i.e. the non-uniform brightness in LCDs, occurred upon the completion of chip-on-glass (COG) packaging of silicon IC driver through the thermal bonding of anisotropic conducting film (ACF) resulting from the coefficient of thermal expansion (CTE) mismatch between glass substrate and silicon chips. In mid-size TFT-LCD demanding low weight and high mobility, such Mura defect deteriorated as thinner glass plates were introduced and implanted.
In this study, the root-causes of Mura defect induced by COG package were examined and proposed. Then, the impact of thermal bonding temperature and thermo mechanical properties of ACF on Mura defect was investigated. In addition, the effects of dimension and layout of Si chips were also explored. In specific, a 3-D finite element analysis (FEA) model using ANSYSTM was first established to examine the warpage and stress behavior of the glass substrate in order to explore their correlation with light leakage phenomenon. In addition, the simulated warpage data were validated by surface contour measurement tool using surface profiler, KOSAKA ET4000A.
Based on experimental data and numerical analysis, the strong relationship among light leakage defect, warpage and stress behavior was found. Besides, the root-cause of light leakage phenomenon was proposed. The Mura may resulted from the re-orientation of the director of the liquid crystal molecules and/or the orientation of the polymer chains on the alignment layer surface induced by the non-uniform stress resulting from COG packaging. Although the light leakage Mura appeared when the thickness of glass substrate was decreased from 0.5 mm to 0.3 mm, reducing ACF thermal bonding temperature from 180 to 160oC or reducing ACF modulus can effectively eliminate Mura defect. Numerical modeling was also utilized to analyze the effectiveness of the dimension and layout of Si chips on Mura improvement. A low cost and effective solution can be realized through thin silicon die, shorter die in length or the use of dummification.
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