GaN LED Underfill Deposition for Substrate Removal
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Solution Overview
Problem
Conventional underfill materials for GaN LEDs lack uniform support, thermal expansion matching, and high-temperature operability, leading to stress and inefficient heat sinking during substrate removal and high-power operation.
Innovation Solution
A method involving the deposition of a patterned and polished underfill layer on GaN LEDs before substrate removal, using materials like polyimide with high glass transition temperature and added fillers for improved thermal expansion matching and support, which is applied before mounting to a submount and helps in singulating the devices.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional underfill materials are used for GaN LEDs, then the LED can be mounted and operated, but the underfill lacks uniform support, thermal expansion matching, and high-temperature operability, leading to stress and inefficient heat sinking
Solution Approach 1:
The patent changes the material parameters of the underfill by using a deposited layer with controlled composition and structure. The underfill layer is deposited with specific thickness (e.g., 1-10 micrometers) and material composition that provides improved thermal expansion matching with GaN LED layers, enabling reliable operation at high temperatures up to 150°C or higher while reducing thermal stress.
Solution Approach 2:
The patent employs composite material structure where the underfill layer is deposited as a distinct layer between the GaN LED and substrate. This deposited underfill layer combines beneficial properties: mechanical compliance for stress reduction, thermal expansion matching with GaN, and improved thermal conductivity for heat sinking, creating a composite structure that addresses multiple performance requirements simultaneously.
2Strength
If conventional underfill materials are used, then the LED can be assembled, but the support is non-uniform and contains voids, leading to mechanical instability during substrate removal
Solution Approach 1:
The patent replaces the conventional mechanical underfill application method (which involves dispensing and flowing liquid underfill material) with a deposition process. This deposition method (such as sputtering, evaporation, or CVD) creates a uniform, void-free underfill layer directly on the LED structure, eliminating the voids and non-uniformity inherent in liquid-based underfill application while providing consistent mechanical support.
3Loss of energy
If conventional underfill materials are used, then the LED can be mounted to submount, but thermal conductivity is insufficient, leading to inefficient heat sinking during high-power operation
Solution Approach 1:
The patent changes the thermal conductivity parameter of the underfill by selecting deposited material with superior thermal properties. The deposited underfill layer has enhanced thermal conductivity compared to conventional organic underfill materials, enabling efficient heat transfer from the GaN LED to the substrate and heat sink, thus supporting high-power operation with improved energy efficiency and reduced thermal loss.
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 provides uniform, void-free support, reduces thermal conductivity issues, and enhances high-temperature operability by matching thermal expansion and improving mechanical support, thus preventing LED layer fractures and ensuring reliable high-power performance.
Implementation Method 1
a deposited underfill layer is provided over the LED layers
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
Data Source
Figure 1A~1D
Figure 2A~2E
Figure 3~4B
AI summary
A light emitting diode (LED) is fabricated using an underfill layer that is deposited on either the LED or the submount prior to mounting the LED to a submount. The deposition of the underfill layer prior to mounting the LED to the submount provides for a more uniform and void free support, and increases underfill material options to permit improved thermal characteristics. The underfill layer may be used as support for the thin and brittle LED layers during the removal of the growth substrate prior to mounting the LED to the submount. Additionally, the underfill layer may be patterned to and/or polished back so that only the contact areas of the LED and/or submount are exposed. The patterns in the underfill may also be used as a guide to assist in the singulating of the devices.