Touch Panel Probe Pad Design for Block Dim Prevention
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Solution Overview
Problem
In liquid crystal display devices with touch screens, noise from parasitic capacitance in lighting-test switching elements causes block dim issues during testing, and these switching elements are unnecessary in display mode, leading to potential leakage currents and display failures.
Innovation Solution
The design includes a touch panel with a common voltage probe pad larger than the common voltage output pad, allowing a jig bar to apply a test signal directly, eliminating the need for lighting-test switching elements on touch routing lines, thereby preventing common voltage distortion and block dim.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If lighting-test switching elements are used to enable lighting test on touch routing lines, then the lighting test can be performed, but noise occurs due to parasitic capacitance causing block dim
Solution Approach 1:
The patent extracts and removes the lighting-test switching elements from the circuit. By eliminating these switching elements, the parasitic capacitance causing noise and block dim is removed, while the lighting test function is preserved through direct connection of test pads to touch routing lines.
Solution Approach 2:
The patent introduces test pads as intermediary elements that directly connect to touch routing lines. These test pads serve as mediators that enable lighting tests without requiring switching elements, thus avoiding the parasitic capacitance issue while maintaining test capability.
2Device complexity
If lighting-test switching elements are retained in the completed product, then the structure remains simple, but leakage current occurs causing common voltage distortion and display failure
Solution Approach 1:
The patent extracts and removes the lighting-test switching elements from the final product structure. This elimination prevents leakage current paths while maintaining circuit simplicity through direct pad connections, thereby improving display reliability without significantly increasing complexity.
3Reliability
If laser cutting is used to disconnect pads from lighting-test switching elements, then leakage current is prevented, but manufacturing cost increases and re-testing becomes impossible
Solution Approach 1:
The patent extracts the lighting-test switching elements entirely from the design, eliminating the need for laser cutting disconnection. This approach prevents leakage current without adding manufacturing steps or costs, and maintains the ability to perform lighting tests during production.
Solution Approach 2:
The patent designs the circuit from the beginning without lighting-test switching elements, performing the elimination action in advance during design rather than requiring post-manufacturing laser cutting. This preliminary design decision prevents leakage current while avoiding additional manufacturing costs and preserving re-test capability.
Data Source
AI summary
A liquid crystal display device having a touch screen and a test method of a touch panel are provided that can prevent a block dim that may occur in a lighting test. The liquid crystal display device includes common voltage probe pads, which are connected to common voltage output pads and are larger than the common voltage output pads, in a non-display area of the touch panel.