COF Pad Insulation Structure to Prevent Ion Migration in Displays
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Solution Overview
Problem
As the resolution of display panels increases, the number of pads on chip-on-film (COF) structures connecting display panels and printed circuit boards (PCBs) also increases, leading to higher potential differences between pads. This, combined with complex stacking structures and potential moisture ingress, results in ion migration from metal pads, causing electrical defects like short circuits.
Innovation Solution
The implementation of an insulating film on the side surfaces of pads on the chip-on-film (COF) structure prevents ion migration between adjacent pads, thereby reducing electrical defects. This configuration includes a film circuit board with pads at selected distances, a thin film pattern covering the pads, and an insulating film on the pad surfaces.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the number of pads on the chip-on-film is increased to support higher resolution display panels, then the electrical connection capability is improved, but the potential difference between pads increases causing ion migration and electrical defects
Solution Approach 1:
An insulating film is introduced as an intermediary substance between adjacent metal pads on the chip-on-film. This insulating film acts as a barrier that prevents ion migration from occurring between pads while still allowing the pads to perform their electrical connection function. The insulating film is applied to the side surfaces and top surfaces of the pads, creating a protective layer that blocks the harmful ion migration path without interfering with the electrical connectivity purpose of the pads.
2Reliability
If chemical treatments are used to prevent ion migration between pads, then the electrical defects are reduced, but hazardous substances are introduced into the manufacturing process
Solution Approach 1:
The patent replaces chemical treatment methods with a physical barrier approach. Instead of using chemical substances to prevent ion migration, an insulating film is applied as a physical barrier on the pad surfaces. This mechanical/physical solution (applying an insulating coating) substitutes for chemical treatments, achieving the same goal of preventing ion migration without introducing hazardous chemicals into the manufacturing process.
3Adaptability or versatility
If the adhesion between signal lines and pads is decreased due to complex stacking structure, then the manufacturing flexibility is improved, but moisture ingress increases leading to ion migration
Solution Approach 1:
The protective function is segmented into multiple layers: the insulating film is applied specifically to the pad surfaces where ion migration occurs, while the rest of the structure maintains its complex stacking configuration for manufacturing flexibility. This segmented approach allows the protective function to be localized to where it is most needed (at the pad interfaces) without requiring a complete redesign of the entire stacking structure.
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
The use of an insulating film on the side surfaces of pads on the chip-on-film (COF) effectively reduces ion migration and associated electrical defects, such as short circuits, without requiring chemical treatments or hazardous substances.
Implementation Method 1
an insulating film provided on side surfaces of pads provided on the chip-on-film to prevent ion migration between adjacent pads
Data Source
AI summary
Provided is a display device. A display panel includes a plurality of subpixels and is supplied with an electrical signal through pixel pads to drive the subpixels. At least one driving circuit is mounted on a chip-on-film. The chip-on-film delivers the electrical signal through film pads electrically connected to the pixel pads. The chip-on-film includes an insulating film provided on side surfaces of the film pads.