Low Thermal Resistance LED Package Using Planar Submount
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Solution Overview
Problem
Traditional LED packages suffer from high thermal resistance due to lengthy heat conduction paths and low thermal conductivity materials, leading to increased junction temperatures, reduced light brightness, and potential breakage from stress caused by bonding wires, which are costly and inefficient.
Innovation Solution
A thin metal sheet is etched into sections for a submount and lead frames, held together with an insulating cup, eliminating the need for a separate heat sink and reducing the package thickness, while using a transparent lens to enhance luminance and optical flexibility, and allowing for series or parallel electrical connections.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If bonding wires are used to couple the LED chip to lead frames, then electrical connection is achieved, but thermal resistance increases and reliability decreases due to stress and heat generation
Solution Approach 1:
The patent removes the bonding wire component entirely from the LED package structure. The LED chip is directly mounted on the lead frame without intermediate bonding wires, eliminating the source of thermal resistance and mechanical stress associated with wire bonding. This extraction of the problematic element directly resolves the contradiction between reliability and energy loss.
Solution Approach 2:
The patent merges the electrical connection function and thermal conduction function into a single integrated lead frame structure. The lead frame serves both as the electrical terminal and as the primary heat dissipation path, eliminating the need for separate bonding wires. This consolidation improves both reliability by removing weak connection points and reduces thermal resistance by creating a direct thermal pathway.
2Temperature
If traditional lead frame structures are used, then mechanical support is provided, but thermal resistance is excessive due to small cross-sectional area and long heat conduction path
Solution Approach 1:
The patent transitions from a traditional three-dimensional heat conduction path through bonding wires and lead frames to a two-dimensional planar heat dissipation structure. The lead frame is designed with an extended surface area that spreads heat laterally across the package footprint, reducing the effective thermal resistance by providing multiple parallel heat conduction paths and increasing the cross-sectional area for heat flow.
Solution Approach 2:
The lead frame is segmented into multiple thermal conduction paths that originate from different points on the LED chip and converge at the package leads. This segmentation creates parallel heat flow channels, reducing the overall thermal resistance by providing multiple routes for heat to escape simultaneously rather than relying on a single long conduction path.
3Ease of manufacture
If traditional LED package structures are used, then basic functionality is achieved, but production cost is high due to gold or aluminum bonding wires
Solution Approach 1:
The patent replaces expensive gold or aluminum bonding wires with a inexpensive copper-based lead frame structure. The lead frame material, while less expensive, is designed to provide sufficient mechanical support and electrical connection without the need for precious metals. This substitution dramatically reduces material costs while maintaining functional reliability through the integrated design.
Solution Approach 2:
The lead frame is designed to perform multiple functions simultaneously: providing mechanical support for the LED chip, establishing electrical connections, and serving as the primary heat dissipation pathway. This multi-functionality eliminates the need for separate bonding wires and reduces the number of manufacturing steps, thereby lowering production costs while improving reliability through fewer potential failure points.
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 design significantly lowers thermal resistance, reduces production costs, and maintains final temperature stability while improving light transmission and optical versatility.
Implementation Method 1
Since the light emitting diode chip is the sole source of heat generation, and only a negligible amount of this energy is radiated as electromagnetic waves, the bulk of the energy is transformed into heat. Thus the thermal-resistance formula can be rewritten as: RθJ-P=(TJ−TP)/(If−If)
Implementation Method 2
The LED 10 is coated with transparent glue, leaving only the leads exposed for external connection. Another prior art is shown in FIG. 2. A LED chip 10 is mounted on a printed circuit board 13, and is wire bonded with gold or aluminum wire 14 to surface contact leads of the printed circuit board. The structure is covered with transparent glue 12.
Data Source
AI summary
A LED chip is bonded on a large submount serving as a heat sink. The submount is punched out from a thin metal sheet together with two other sections of lead frames for the LED and held together with insulating material. The planar structure makes the package thin. A transparent lens may be mounted over the submount. More than one LED of same or different color can be mounted on the submount.