Patterned Conductive Ball Bonding for Fine-Pitch Micro LED Modules
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Solution Overview
Problem
During the manufacturing of display modules with inorganic light emitting diodes of 100 μm or less, conductive balls often fail to provide good contact and tend to cluster together due to their high density, especially at fine or ultra-fine pitches, leading to connectivity issues.
Innovation Solution
The use of an anisotropic conductive film with patterned conductive balls aligned in grooves on a mold substrate, where the grooves are treated to prevent sticking and the balls are inserted using vacuum suction, allows for effective electrical and physical connection between light emitting diodes and substrate electrode pads without clustering.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If inorganic light emitting diodes are placed with high density at fine or ultra-fine pitch, then the display module achieves higher resolution and better performance, but the conductive balls fail to provide good contact and tend to cluster together
Solution Approach 1:
The patent introduces a bonding member as an intermediary component between the substrate and light emitting diodes. This bonding member includes a adhesive layer with conductive balls embedded within it, serving as a mediator that ensures reliable electrical and physical connection. The bonding member's structure with conductive balls dispersed in adhesive material allows it to bridge the gap between substrate electrode pads and LED electrodes effectively, even at ultra-fine pitch distances of 500 μm or less.
Solution Approach 2:
The patent changes the physical and chemical parameters of the bonding member to optimize contact quality. The adhesive layer uses specific materials with controlled viscosity, curing characteristics, and adhesive strength. The conductive balls are embedded at specific concentrations and depths within the adhesive layer. These parameter changes ensure that the bonding member maintains reliable electrical connection while preventing conductive ball clustering, enabling successful bonding at ultra-fine pitch distances.
2Productivity
If inorganic light emitting diodes are placed with high density at fine or ultra-fine pitch, then the display module achieves higher resolution and better performance, but the conductive balls tend to cluster together
Solution Approach 1:
The patent applies local quality by creating a non-uniform distribution pattern of conductive balls within the bonding member. The conductive balls are embedded in the adhesive layer at specific locations corresponding to the positions of electrode pads and LED electrodes. This localized placement ensures that conductive balls are present where needed for electrical connection while avoiding clustering in irrelevant areas. The bonding member thus has different properties in different locations: high conductive ball density at connection points and low density elsewhere.
3Reliability
If conductive balls are used to connect light emitting diodes and substrate electrode pads, then electrical connection is achieved, but at ultra-fine pitch the contact quality deteriorates and clustering occurs
Solution Approach 1:
The patent applies preliminary action by pre-embedding conductive balls into the adhesive layer before the bonding process. The conductive balls are positioned within the adhesive layer at predetermined locations that correspond to future contact points with electrode pads and LED electrodes. This preliminary arrangement ensures that when the bonding member is applied, conductive balls are already in optimal positions for electrical connection, eliminating the need for precise real-time alignment during bonding and ensuring reliable contact even at ultra-fine pitch distances.
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 solution ensures reliable contact and prevents clustering of conductive balls, enhancing the manufacturing yield and stability of connections between micro LEDs and substrate pads, even at high densities, thereby improving the display module's performance and reliability.
Implementation Method 1
the balls are inserted using vacuum suction
Implementation Method 2
a bonding member including an adhesive layer stacked on one surface of the substrate and a plurality of conductive balls disposed in the adhesive layer
Implementation Method 3
a plurality of light emitting diodes including electrodes connected to the plurality of electrode pads by the plurality of conductive balls
Data Source
AI summary
A display module is provided. The display module includes: a substrate partitioned into a plurality of pixel regions and including a plurality of electrode pads disposed in the pixel regions; a bonding member including an adhesive layer stacked on one surface of the substrate and a plurality of conductive balls disposed in the adhesive layer; and a plurality of light emitting diodes including electrodes connected to the plurality of electrode pads by the plurality of conductive balls, in which the plurality of conductive balls are patterned as a conductive region corresponding to the plurality of electrode pads.