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Research Papers

Hygromechanical Analysis of Liquid Crystal Display Panels

[+] Author and Article Information
Toru Ikeda

Department of Mechanical Engineering,
Kagoshima University,
1-21-40, Korimoto,
Kagoshima 890-0065, Japan
e-mail: ikeda@mech.kagoshima-u.ac.jp

Tomonori Mizutani

e-mail: mizutani@solid.me.kyoto-u.ac.jp

Kiyoshi Miyake

e-mail: miyake@solid.me.kyoto-u.ac.jp

Noriyuki Miyazaki

e-mail: miyazaki@mech.kyoto-u.ac.jp

Department of Mechanical
Engineering and Science,
Kyoto University,
Kyoto Daigaku Katsura,
Nishikyo-ku,
Kyoto 615-8540, Japan

Contributed by the Electronic and Photonic Packaging Division of ASME for publication in the JOURNAL OF ELECTRONIC PACKAGING. Manuscript received August 26, 2010; final manuscript received July 10, 2013; published online November 5, 2013. Assoc. Editor: Yutaka Tsukada.

J. Electron. Packag 135(4), 041005 (Nov 05, 2013) (8 pages) Paper No: EP-10-1084; doi: 10.1115/1.4025527 History: Received August 26, 2010; Revised July 10, 2013

Liquid crystal displays (LCDs) are getting larger, and the homogeneity of an LCD panel is becoming very important for the quality of the display. Inhomogeneity in an LCD panel can be caused by inhomogeneity of its materials and the defective production process, warpage of the panel due to changes in the temperature and humidity, and so on. In this study, we developed a scheme of hygromechanical analysis to reduce the warpage of an LCD. First, we measured the diffusion coefficients and Henry's law coefficients of the respective components of an LCD using a thermogravimetric analyzer (TGA) under controlled humidity. We then measured the coefficients of moisture expansion (CME) of the components using a humidity-controlled thermomechanical analyzer (TMA). We analyzed the hygromechanical deformations of the respective components, a polarizing plate and an LCD panel using the finite element method (FEM) with measured diffusion coefficients, Henry's law coefficients and the CMEs of the respective components. The analyzed deformations of the respective components corresponded quantitatively with the deformations measured experimentally. However, the analyzed deformation of the polarizing plate did not correspond with the measured deformation perfectly. A polarizing plate is made by sandwiching a polarizer between two sheets of protection film. We ignored the effect of the thin boundary layer between the polarizer and its protecting film in this analysis, and the effect of this boundary layer on the diffusion of moisture may have caused the difference between the analysis and the measurement. The expected warpage of the analyzed LCD corresponded qualitatively with the measured warpage. However, the numerical analyzed strains near the edge of the LCD panel strongly shifted to the compression side compared to the experimental measured strains. A possible reason for this shift was the difference in the boundary condition at the edge of the LCD panel between the numerical analysis and the experimental measurement. The actual edge of the LCD panel was fastened by a bezel, and the contact condition between the LCD panel and the bezel was ambiguous. To perform a quantitative analysis, we will need to investigate the contact condition between the LCD panel and the bezel and introduce it to the numerical analysis. This is left for a future study. We qualitatively investigated the warpage of LCDs with two types of protecting film and different directions of polarizing plates using the developed technique of FEM analysis.

Copyright © 2013 by ASME
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References

Figures

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Fig. 1

Structure of an LCD panel (the MD directions of the upper and lower polarizer sheets are orthogonal)

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Fig. 2

Measured and analyzed absorbed weight of water in PRTF1

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Fig. 3

Measured and analyzed absorbed weight of water in PRTF2

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Fig. 4

Measured and analyzed absorbed weight of water in an adhesive

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Fig. 5

Measured and analyzed absorbed weight of water in a polarizer

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Fig. 6

Arrhenius plot of Henry's law constant

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Fig. 7

Arrhenius plot of the diffusion coefficient

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Fig. 8

Measured and analyzed hygroscopic strain of PRTF1 at 40 °C

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Fig. 9

Measured and analyzed hygroscopic strain of a polarizer whose longitudinal direction corresponds with the MD direction at 40 °C

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Fig. 10

Measured and analyzed hygroscopic strain of a polarizer whose longitudinal direction corresponds with the TD direction at 40 °C

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Fig. 13

Measured and analyzed hygroscopic strain of a polarizing plate at 40 °C and 60% RH

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Fig. 11

Moisture concentration-hygrostrain–temperature in PRTF1

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Fig. 12

Moisture concentration-hygrostrain in a polarizer

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Fig. 14

Locations of strain gauges on an LCD panel

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Fig. 15

Measured hygrostrain on an upper surface

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Fig. 16

Measured hygrostrain on a lower surface

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Fig. 17

Analyzed model of a quarter of an LCD

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Fig. 18

Analyzed hygrostrain on an upper surface

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Fig. 19

Analyzed hygrostrain on a lower surface

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Fig. 20

Variations of the vertical displacements at the centers of LCD panels

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Fig. 21

Variations of the nodal reaction forces at the corners of LCD panels

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