TiO2-Infused LED Underfill Reflective Layer
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Solution Overview
Problem
Existing methods for reflecting light emitted by LEDs on a submount surface are inefficient, as they require additional process steps and materials that can absorb light, such as epoxy underfill turning black with UV exposure, and existing reflective metal deposits are not easily integrated with the submount's top metal pattern.
Innovation Solution
A silicone molding compound infused with TiO2 powder is used as an underfill material to form a reflective layer around LEDs, which is injection or compression molded over the submount wafer, providing a flat reflective surface without additional process steps, and microbead blasting exposes the LED tops while maintaining the reflective layer's integrity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If epoxy underfill is used and exposed to UV light, then mechanical support is provided, but the epoxy turns black and absorbs light
Solution Approach 1:
The patent uses a composite underfill material consisting of silicone resin combined with TiO2 (titanium dioxide) particles. The TiO2 provides high reflectivity (over 85% at 5% concentration, over 90% at 10% concentration) while the silicone resin provides mechanical support. This composite material simultaneously achieves both mechanical strength and light reflection without the blackening problem of epoxy under UV exposure.
2Loss of energy
If reflective metal ring is deposited around LED, then light reflection is improved, but additional process steps and insulation requirements are introduced
Solution Approach 1:
The patent merges two separate functions into a single material: the underfill material now simultaneously provides mechanical support and light reflection. By incorporating TiO2 particles into the silicone underfill, the reflective layer is created as an integral part of the underfill application process, eliminating the need for separate metal ring deposition and insulation steps.
Solution Approach 2:
The patent extracts the reflective function from the traditional metal ring approach and integrates it directly into the underfill material itself. This eliminates the need for separate reflective layer deposition processes and the associated insulation requirements, simplifying the overall device structure and manufacturing process.
3Loss of energy
If TiO2 percentage exceeds 5% of total filler content, then reflectivity increases to over 85%, but material composition changes
Solution Approach 1:
The patent systematically studies and optimizes the TiO2 concentration parameter, finding that 5% TiO2 provides over 85% reflectivity while 10% TiO2 provides over 90% reflectivity. The silicone resin matrix maintains structural stability across this composition range, allowing flexible adjustment of reflectivity based on application requirements without compromising mechanical integrity.
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 TiO2-infused underfill material achieves over 85% reflectivity, increasing light output by preventing absorption by the submount without extra process steps, and the reflective layer is electrically insulating and thermally stable, supporting LED semiconductor layers during substrate removal.
Implementation Method 1
a silicone molding compound containing TiO2 powder as filler (or other white powder) is used as the underfill, and the underfill material also forms a substantially flat reflective layer surrounding each of the LEDs
Implementation Method 2
the exposed surface of the TiO2-infused layer is then microbead blasted to expose the top surface of each LED
Data Source
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AI summary
An underfill formation technique for LEDs molds a reflective underfill material to encapsulate LED dies mounted on a submount wafer while forming a reflective layer of the underfill material over the submount wafer. The underfill material is then hardened, such as by curing. The cured underfill material over the top of the LED dies is removed using microbead blasting while leaving the reflective layer over the submount surface. The exposed growth substrate is then removed from all the LED dies, and a phosphor layer is molded over the exposed LED surface. A lens is then molded over the LEDs and over a portion of the reflective layer. The submount wafer is then singulated. The reflective layer increases the efficiency of the LED device by reducing light absorption by the submount without any additional processing steps.