LED Substrate Segmentation for Light Extraction and Bonding
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Solution Overview
Problem
Conventional light emitting devices with aluminum oxide substrates and silver wirings suffer from luminous decay due to sulfurization at die bonding areas, and there is a need for enhanced light extraction efficiency and cost reduction in LED manufacturing.
Innovation Solution
A light emitting device design featuring a Zener diode on a polygonal extension area of the substrate, which does not block light from LED chips, combined with a substrate made of a mixture of aluminum oxide and an inorganic component for improved reflectivity, and a reduced upper metal layer area to increase bonding strength and reduce phosphor powder usage, using screen printing for metal layer formation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a Zener diode is deposited on the central region of the substrate, then electrical protection is provided, but light from LED chips is blocked reducing light extraction efficiency
Solution Approach 1:
The substrate surface is segmented into a central region for LED chip mounting and a peripheral region for Zener diode deposition. This spatial segmentation allows the Zener diode to provide electrical protection without blocking light from the LED chips located in the central region, thereby resolving the contradiction between reliability and light extraction efficiency.
Solution Approach 2:
Different functional zones are created on the substrate with distinct properties: the central region is optimized for light emission with high transparency and smooth surface, while the peripheral region is designed for electrical protection components. This local differentiation allows each zone to perform its specific function optimally without interfering with the other.
2Reliability
If the upper metal layer area is increased to improve electrical connection, then electrical conductivity is enhanced, but bonding area between encapsulant and substrate is reduced weakening bonding strength
Solution Approach 1:
The electrical connection function is segmented from the upper metal layer to dedicated conductive patterns and interconnect structures. This allows the upper metal layer to be minimized in area while maintaining sufficient electrical connectivity through optimized conductive pathways, thereby preserving maximum bonding area between the encapsulant and substrate.
Solution Approach 2:
Electrical connection is achieved not only through planar metal layers but also through three-dimensional conductive structures including vias, through-holes, and vertical interconnects. This dimensional transition allows electrical conductivity to be maintained with reduced planar metal area, freeing up surface area for stronger encapsulant-substrate bonding.
3Manufacturing precision
If conventional thin film deposition is used for metal layers, then manufacturing precision is achieved, but manufacturing cost is high
Solution Approach 1:
The manufacturing process parameters are changed from conventional thin film deposition to screen printing techniques. Screen printing offers comparable precision for thick metal layers while significantly reducing manufacturing costs through simpler equipment requirements, faster processing speeds, and lower material waste, thereby resolving the contradiction between manufacturing precision and cost.
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 design enhances light extraction efficiency, increases bonding strength, and reduces manufacturing costs by effectively reflecting light and minimizing phosphor powder usage, while preventing light blockage and sulfurization issues.
Implementation Method 1
the substrate made of a mixture of aluminum oxide and a desired inorganic component has superior light reflectivity. Therefore, light irradiated to the substrate from the LED chips would be reflected more effectively
Implementation Method 2
deposition of a Zener diode on a polygonal extension area of a central region
Data Source
AI summary
A light emitting device includes a substrate having a top surface, upper and lower metal layers, multiple LED chips, at least one Zener diode, multiple conductive wires and an encapsulant. The top surface includes a central region bounded by an imaginary boundary with a profile conforming to an outline of a circle stacked with a polygon. The central region has a die bonding area corresponding to the circle, and at least one polygonal extension area formed outside the die bonding area. The upper metal layer includes multiple conducting pads surrounding the central region. The LED chips are disposed on the die bonding area. The Zener diode is disposed on the polygonal extension area. The encapsulant is disposed on the substrate and covers the LED chips.