Flip-Chip LED Anisotropic Conductive Film Thermal Stress
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Solution Overview
Problem
Conventional light emitting devices face reliability issues due to thermal stress caused by differences in thermal expansion between Au bumps and underfill resin, leading to potential cracking of the semiconductor layer after substrate removal in flip-chip mounting processes.
Innovation Solution
The method involves using anisotropic conductive material with conductive particles and a first resin to electrically connect the light emitting element to the support member, allowing for flexible electrical connection and uniform thermal stress distribution, thereby reducing the risk of semiconductor layer breakage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If Au bumps are firmly fixed to wirings by ultrasonic bonding, then electrical connection is achieved, but thermal stress causes semiconductor layer cracking
Solution Approach 1:
The patent introduces an anisotropic conductive film as an intermediary material between the Au bumps and the wirings. This film contains conductive particles that enable electrical connection while providing a compliant interface that absorbs thermal expansion differences, preventing direct stress transmission to the semiconductor layer.
Solution Approach 2:
The patent changes the mechanical properties of the connection interface by using a material with different compliance characteristics. The anisotropic conductive film has higher compliance compared to direct ultrasonic bonding, allowing it to deform and absorb thermal stress while maintaining electrical conductivity through its conductive particles.
2Illumination intensity
If substrate is removed to improve light extraction efficiency, then vertical light extraction is enhanced, but semiconductor layer becomes vulnerable to thermal stress
Solution Approach 1:
The patent applies the anisotropic conductive film before removing the substrate. This preliminary action ensures that the compliant connection interface is already in place to absorb thermal stress, protecting the semiconductor layer even after substrate removal enhances light extraction efficiency.
3Strength
If underfill resin is used to fill space between chip and support member, then mechanical support is provided, but thermal expansion difference causes stress
Solution Approach 1:
The patent uses a composite material system consisting of the anisotropic conductive film with conductive particles embedded in a resin matrix. This composite structure provides both mechanical support through the resin and thermal stress absorption through the compliant film, while maintaining electrical conductivity via the conductive particles.
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 approach enhances both light extraction efficiency and reliability of the light emitting device by mitigating thermal stress and maintaining electrical connection integrity.
Implementation Method 1
electrically connecting the p-side electrode and the n-side electrode of the structure to the p-side wiring and the n-side wiring of the support member, respectively, by anisotropic conductive material containing conductive particles and a first resin
Data Source
Figure 1(a)~1(d)
Figure 2(a)~2(b)
Figure 3(a)~3(b)
AI summary
A method for manufacturing a light emitting device wherein a light emitting element is flip-chip mounted on a support member is provided to realize the light emitting device with both high light extraction efficiency and high reliability. A structure (7) including a substrate (1), a semiconductor layer (5) formed on the substrate (1), and a p-side electrode (6a) and an n-side electrode (6b) formed on the semiconductor layer (5) is prepared. A support member (20) including a p-side wiring (11a) and an n-side wiring (11b) on the same surface is prepared. The p-side and n-side electrodes (6a, 6b) of the structure (7) are electrically connected to the p-side and n-side wirings (11a, 11b) of the support member (20), respectively, using anisotropic conductive material (23) containing conductive particles (21) and a first resin (22). Then, the substrate (1) is removed from the structure (7) to form a light emitting element (9').