Flip-Chip LED Multilayer Electrode for Thermal Stress Buffering
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Solution Overview
Problem
Conventional flip-chip light emitting diodes face issues with internal stress buffering and release due to the low tensile strength of Au electrodes, leading to detachment problems during substrate deformation.
Innovation Solution
A flip-chip light emitting diode with a multilayer metal structure, where the thickest layer is a high-tensile-strength Al conductive metal layer, facilitating stress buffering and current spreading, and including additional layers like Ti, Pt, and Ni for enhanced adhesion and barrier functions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a single-layer Au electrode is used, then electrical and thermal conductivity is improved, but tensile strength is insufficient leading to stress buffering failure
Solution Approach 1:
The patent employs a multilayer composite electrode structure consisting of Au, Cu, and Mo layers. Each layer contributes different properties: Au provides excellent electrical and thermal conductivity, Cu enhances tensile strength and reduces stress, and Mo adds structural support. This composite structure resolves the contradiction by combining materials with complementary properties to achieve both high conductivity and high strength simultaneously.
Solution Approach 2:
The electrode is segmented into multiple functional layers rather than using a single material layer. The Au layer (50-200 nm) handles conductivity, the Cu layer (50-200 nm) provides tensile strength and stress relief, and the Mo layer (50-200 nm) offers structural support. This segmentation allows each layer to optimize for its specific function while working together as an integrated system.
2Adaptability or versatility
If packaging substrate deforms, then mounting flexibility is improved, but internal stress increases causing electrode detachment
Solution Approach 1:
The Cu layer is specifically designed to provide stress relief before the stress can cause damage. Cu has different mechanical properties than Au and the substrate, allowing it to absorb and distribute stress generated during substrate deformation. This beforehand cushioning prevents stress concentration that would otherwise lead to electrode detachment or insulating layer separation.
Solution Approach 2:
The multilayer composite structure with Cu and Mo layers provides differential stress distribution. When the substrate deforms, each layer responds differently due to their distinct mechanical properties, creating a stress-distributing effect that protects the overall structure from damage while maintaining mounting adaptability.
3Strength
If multilayer metal structure is used, then tensile strength and stress buffering are improved, but manufacturing complexity increases
Solution Approach 1:
The patent specifies precise thickness ranges for each layer (50-200 nm for Au, Cu, and Mo layers) to optimize performance while controlling complexity. By defining specific parameter ranges rather than fixed values, the design achieves high strength through the multilayer structure while maintaining manufacturability through standardized thickness specifications that can be controlled with conventional fabrication processes.
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 solution effectively buffers and releases internal thermal stress, improves current spreading, and enhances the reliability of the device by using the Al layer with high tensile strength as the conductive metal layer.
Implementation Method 1
internal thermal stress of the light emitting diode during subsequent use may be well buffered and released
Implementation Method 2
The metal reflective layer is located between the first semiconductor layer and the first barrier layer
Data Source
AI summary
A flip-chip light emitting diode includes an epitaxial structure, a first electrode, and a second electrode. The epitaxial structure includes a first semiconductor layer, a light emitting layer, and a second semiconductor layer. The light emitting layer is located between the first semiconductor layer and the second semiconductor layer. The first electrode is located on the epitaxial structure and is electrically connected to the first semiconductor layer. The second electrode is located on the epitaxial structure and is electrically connected to the second semiconductor layer. The first electrode and/or the second electrode is a multilayer metal structure. The multilayer metal structure includes a metal reflective layer, a first barrier layer, and a conductive metal layer stacked in sequence on the first semiconductor layer. A thickest layer in the multilayer metal structure is the conductive metal layer, and the conductive metal layer is an Al layer.