LED Assembly Metal Support for Laser Lift-Off
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Solution Overview
Problem
Current methods for supporting thin, brittle LED layers during substrate removal are inefficient, requiring underfills that are costly, time-consuming, and induce thermal stresses due to mismatched thermal expansion properties, and lack sufficient mechanical support and thermal conductivity.
Innovation Solution
The process involves forming anode and cathode electrodes on the underside of the LED die that cover at least 85% of the back surface, interconnected with the submount electrodes, allowing for laser lift-off of the growth substrate without underfill, using methods like ultrasonic or thermosonic metal-to-metal interdiffusion or soldering, providing extensive support and matched thermal expansion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If underfill is used to support LED layers during substrate removal, then mechanical support is provided, but manufacturing time increases and thermal stresses are induced due to mismatched thermal expansion properties
Solution Approach 1:
The patent applies preliminary action by forming extensive metal electrodes on the LED layers before substrate removal. These electrodes are prepared in advance to provide mechanical support during the subsequent substrate removal process, eliminating the need for underfill application and curing time.
Solution Approach 2:
The patent uses metal electrodes as an intermediary between the LED layers and the external environment. These electrodes serve dual functions: providing mechanical support during substrate removal and establishing electrical connections, replacing the underfill material's support function while adding electrical functionality.
2Strength
If underfill is used to support LED layers, then mechanical support is provided, but thermal conductivity is insufficient and thermal stresses increase due to mismatched thermal expansion
Solution Approach 1:
The patent changes the material parameters by replacing organic underfill material with metal electrodes. This fundamental parameter change provides both mechanical support and superior thermal conductivity, while the metal's thermal expansion properties better match the LED layers, reducing thermal stresses.
Solution Approach 2:
The patent creates a composite structure where metal electrodes are integrated with the LED layers. This composite approach combines the mechanical support function with high thermal conductivity and matched thermal expansion properties, achieving multiple performance goals simultaneously.
3Reliability
If extensive metal electrodes covering 85% of back surface are used, then mechanical support and thermal conductivity are improved, but device complexity increases
Solution Approach 1:
The patent applies universality by designing metal electrodes that perform multiple functions simultaneously: providing mechanical support during substrate removal, establishing electrical connections, and conducting heat away from the LED layers. This multi-functionality reduces the need for separate components.
Solution Approach 2:
The patent merges the mechanical support function and electrical connection function into a single component structure. The extensive metal electrodes that would traditionally be used only for electrical connections are instead designed to also provide mechanical support, combining multiple functions into one element.
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 reduces manufacturing costs and time, ensures uniform and bubble-free support, maintains high-temperature operability, and enhances thermal conductivity, minimizing thermal stresses and improving LED performance.
Implementation Method 1
removal of the sapphire substrate by a excimer laser ablation process
Implementation Method 2
an ultrasonic transducer rapidly vibrates the LED structure with respect to the submount to create heat at the interface
Implementation Method 3
Pressure is applied to the LED structure while an ultrasonic transducer rapidly vibrates the LED structure with respect to the submount to create heat at the interface. This causes the surface of the gold stud bumps to interdiffuse at the atomic level into the LED electrodes and submount electrodes to create a permanent electrical connection.
Implementation Method 4
enhances thermal conductivity, minimizing thermal stresses
Data Source
AI summary
Described is a process for forming an LED structure using a laser lift-off process to remove the growth substrate (e.g., sapphire) after the LED die is bonded to a submount. The underside of the LED die has formed on it anode and cathode electrodes that are substantially in the same plane, where the electrodes cover at least 85% of the back surface of the LED structure. The submount has a corresponding layout of anode and cathode electrodes substantially in the same plane. The LED die electrodes and submount electrodes are ultrasonically welded together such that virtually the entire surface of the LED die is supported by the electrodes and submount. Other bonding techniques may also be used. No underfill is used. The growth substrate, forming the top of the LED structure, is then removed from the LED layers using a laser lift-off process. The extremely high pressures created during the laser lift-off process do not damage the LED layers due to the large area support of the LED layers by the electrodes and submount.