Flat Panel Display Pad Electrode Contact Hole Design
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Solution Overview
Problem
Conventional flat panel displays (FPDs) face issues with electrical disconnection between the pad portion and the driver IC due to fine contact holes and undercuts, leading to increased contact resistance and deteriorated electrical characteristics.
Innovation Solution
A method of forming a pad portion with a sufficient contact region by creating either one or multiple contact holes in the passivation layer to expose the pad electrode, and forming a reflective layer that overlaps the pad electrode in the contact holes, followed by the deposition of a transparent electrode, ensuring stable electrical connection even with conductive particles not fully filled in the contact holes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If fine contact holes are formed in the passivation layer to expose the pad electrode, then the bonding process can be performed, but electrical disconnection occurs due to undercuts and insufficient contact region
Solution Approach 1:
The patent extends the pad electrode laterally beyond the contact hole boundaries, creating an undercut-free contact region that expands the effective bonding area in the horizontal dimension. This dimensional extension ensures that even if conductive particles miss the contact hole center, they still establish electrical connection with the extended pad electrode region.
Solution Approach 2:
The pad electrode is designed with non-uniform geometry, featuring an extended region with larger lateral dimensions compared to the contact hole region. This local quality variation creates a dedicated bonding area with enhanced contact capability, while maintaining the standard contact hole structure for precise alignment.
2Reliability
If the reflective layer is removed from the pad electrode area to reduce contact resistance, then electrical conductivity improves, but the pad electrode becomes vulnerable to disconnection
Solution Approach 1:
The pad electrode structure is segmented into two functional regions: a contact hole region where the reflective layer is removed to minimize contact resistance, and an extended region that maintains the reflective layer for structural support and additional bonding area. This segmentation allows simultaneous optimization of electrical conductivity and structural integrity.
3Reliability
If multiple contact holes are formed to increase bonding area, then connection reliability improves, but manufacturing complexity and risk of defects increase
Solution Approach 1:
Multiple contact holes are merged into a single extended pad electrode structure, creating one continuous bonding region that encompasses all contact holes. This merging approach maintains the benefits of multiple contact points while simplifying the overall structure and reducing manufacturing complexity compared to treating each contact hole as a separate element.
Data Source
AI summary
A flat panel display, and method of fabricating the same, including a substrate having a display portion and a pad that is arranged on the substrate and is electrically coupled with the display portion. The pad includes a pad electrode arranged on the substrate, a passivation layer arranged on the pad electrode and having only one contact hole that exposes the pad electrode, and a transparent electrode arranged on the passivation layer and the pad electrode. The passivation layer may alternatively have a plurality of contact holes that expose the pad electrode. In this case, the reflective layer pattern is arranged on the passivation layer and the pad electrode, and it exposes portions of the pad electrode in the contact holes. Furthermore, the transparent electrode would be arranged on the reflective layer pattern and the exposed portions of the pad electrode.