Resin Substrate Warpage Compensation via Rear Inorganic Film Thickness
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Solution Overview
Problem
Active matrix substrates using resin substrates often warp due to differences in thermal expansion coefficients and moduli between the resin substrate and the inorganic films, leading to defects in electrical connections, mechanical stress, and flatness issues in liquid crystal display devices.
Innovation Solution
A rear surface-side inorganic film with a predetermined thickness is added to the resin substrate to compensate for the warpage caused by the front surface-side inorganic films, using the linear elastic modulus, coefficient of linear expansion, and thickness to set the curvature diameter within a specific range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a resin substrate is used instead of glass to reduce weight and improve flexibility, then the substrate becomes more suitable for modern display devices, but warpage occurs due to differences in thermal expansion coefficients between the resin substrate and inorganic films
Solution Approach 1:
The patent applies composite materials by creating a multi-layer structure consisting of a resin substrate combined with multiple inorganic films (first inorganic insulating film, second inorganic insulating film, and protective film). This composite structure compensates for the thermal expansion differences between the resin substrate and individual inorganic films, thereby preventing warpage while maintaining the advantages of using a resin substrate.
Solution Approach 2:
The patent applies local quality by assigning different functions and properties to different layers of the substrate structure. The first inorganic insulating film provides electrical insulation, the second inorganic insulating film provides additional structural support and thermal expansion compensation, and the protective film provides surface protection. Each layer is optimized for its specific function to collectively solve the warpage problem.
2Reliability
If inorganic films are formed on the resin substrate at high temperature (300°C or more), then the TFTs can be properly formed, but the warpage of the substrate increases due to thermal contraction differences
Solution Approach 1:
The multi-layer composite structure of resin substrate plus multiple inorganic films provides thermal expansion compensation during high-temperature processing. The combination of materials with different thermal properties ensures that the overall structure maintains flatness even when subjected to temperatures of 300°C or more during TFT formation.
Solution Approach 2:
The patent applies beforehand cushioning by pre-designing the multi-layer structure with appropriate thickness ratios before manufacturing. The first inorganic insulating film is set to be thicker than the second inorganic insulating film, creating a built-in compensation mechanism that anticipates and counteracts the thermal contraction that will occur during high-temperature processing.
3Ease of manufacture
If the active matrix substrate is separated from the supporting substrate using laser ablation, then the resin substrate can be released, but warpage and curling occur due to differential contraction
Solution Approach 1:
The multi-layer composite structure remains intact during laser ablation separation from the supporting substrate. The combined structure of resin substrate and multiple inorganic films provides sufficient mechanical strength to prevent warpage and curling during the separation process, enabling easy manufacture while maintaining substrate flatness.
Solution Approach 2:
The patent addresses curvature control by designing the multi-layer structure to maintain a substantially flat configuration. The specific arrangement and thickness ratios of the inorganic films counteract the natural tendency toward curling that would occur during separation, ensuring the substrate remains flat for subsequent mounting operations.
4Reliability
If multiple inorganic films are formed on the resin substrate, then the electrical and insulating properties are improved, but the device complexity and manufacturing steps increase
Solution Approach 1:
The patent applies universality by designing the inorganic films to serve multiple functions simultaneously. The first and second inorganic insulating films provide both electrical insulation and structural support, while also contributing to thermal expansion compensation. The protective film provides both surface protection and additional insulation, reducing the need for separate specialized layers.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach effectively suppresses warpage and enhances the workability of the active matrix substrate, improving electrical connections, reducing mechanical stress, and maintaining the flatness of the display device.
Implementation Method 1
since the coefficient of linear expansion of the resin substrate is higher than that of an inorganic film formed thereon, the rate of contraction of the resin substrate obtained when a temperature of approximately 250° C. to 300° C. at which the inorganic film is formed is decreased to room temperature is higher than the rate of contraction of the inorganic film
Implementation Method 2
laser light is irradiated from a rear surface side of the supporting substrate, and an ablation phenomenon caused by the laser light is used for the separation
Data Source
AI summary
The thickness of a rear surface-side inorganic film (9) formed from the same material as that of each of front surface-side inorganic films (11, 13, and 16) and provided at a rear surface side of a resin substrate (10) having a heat resistance is set in a predetermined range with respect to the total thickness of the front surface-side inorganic films (11, 13, and 16) so that the curvature diameter calculated based on the linear elastic modulus, the coefficient of linear expansion, and the thickness of the resin substrate (10); the linear elastic moduli, the coefficients of linear expansion, and the total thickness of the front surface-side inorganic films (11, 13, and 16); and the linear elastic modulus, the coefficient of linear expansion, and the thickness of the rear surface-side inorganic film (9) is 20 mm or more or −20 mm or less.