COF Pad Layout for Signal Stability
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Solution Overview
Problem
The challenge is to maintain stable high-speed signal transmission and structural stability in display devices with reduced widths of chip on film (COF) and flexible printed circuit board (FPCB) while ensuring sufficient pad connection space, as narrower widths lead to connection issues and signal instability due to differing signal path lengths.
Innovation Solution
The solution involves arranging COF and FPCB pads in two rows, with dummy pads in the high-speed signal region to equalize signal path lengths and using these dummy pads to stabilize wire connections, ensuring that both positive and negative signals are transmitted equally, and removing unnecessary via structures to enhance structural stability during contact.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If the widths of chip on film and flexible printed circuit board are reduced to decrease device size, then device size is reduced, but pad connection stability and signal transmission stability deteriorate
Solution Approach 1:
The patent transitions from a single-row pad arrangement to a two-row pad arrangement on the chip on film. This dimensional change allows pads to be distributed across two rows, improving connection stability and signal transmission reliability while maintaining reduced device size. The two-row configuration provides better mechanical support and electrical connection stability without increasing the overall device footprint.
Solution Approach 2:
The patent introduces dummy pads as intermediary elements between the functional pads and the driver circuit. These dummy pads serve as buffer structures that enhance the mechanical stability of wire connections and provide reference planes for high-speed signal transmission. The dummy pads do not carry functional signals but improve the overall connection reliability and signal integrity.
2Volume of moving object
If the widths of chip on film and flexible printed circuit board are reduced to decrease device size, then device size is reduced, but high-speed signal transmission stability deteriorates due to differing signal path lengths
Solution Approach 1:
By arranging pads in two rows, the patent creates multiple signal transmission paths that can be equalized in length. This two-dimensional pad layout allows for better control of signal path lengths, ensuring that differential signals (positive and negative) travel equal distances to maintain signal integrity in high-speed transmissions.
Solution Approach 2:
Dummy pads act as intermediary reference structures that help equalize signal path lengths. By positioning dummy pads strategically in the two-row configuration, the patent ensures that functional pads have matched signal path lengths to the driver, which is critical for maintaining stability in high-speed differential signal transmissions.
3Reliability
If pads are arranged in two rows to improve connection stability, then pad connection stability improves, but device complexity increases
Solution Approach 1:
The patent segments the pad arrangement into two distinct rows, with functional pads in one row and dummy pads in the other row. This segmentation simplifies the overall design by clearly separating functional elements from structural support elements, making the two-row configuration more manageable and less complex than a fully populated two-row functional pad arrangement.
Solution Approach 2:
The patent applies different qualities to different regions of the pad structure. Functional pads are designed for electrical connection, while dummy pads are designed for mechanical support and signal reference. This local differentiation of quality allows the two-row arrangement to achieve improved stability without requiring all pads to be fully functional, thereby reducing overall complexity.
Data Source
AI summary
A display device according to an example embodiment of the present invention includes a display panel configured to display an image, the display panel including a plurality of pixels, a chip on film (COF) coupled to the display panel, the COF comprising a driver, a plurality of COF wires and a plurality of COF pads, and a flexible printed circuit board (FPCB) coupled to the COF, the FPCB including a plurality of FPCB wires and a plurality of FPCB pads, wherein the plurality of COF pads are arranged in two rows, and wherein one or more COF pads of the plurality of COF pads in a first row of the two rows are one or more dummy pads.