LED Dies Bonded to Lead Frame Strips for Thermal Management
Solution Overview
Problem
High power LEDs in automotive applications face challenges with heat dissipation due to their small size and complex thermal design, especially when multiple LEDs are connected in series, which is exacerbated in enclosed spaces like automobile headlights.
Innovation Solution
A modular LED structure where high power vertical LEDs are connected in parallel and series, with each LED having a bottom metal pad serving as a cathode and thermal conductor, and a top electrode as a wire bond pad, using wide copper strips for both heat sinking and reflection, and encapsulated in a thermally conductive material to enhance heat dissipation and light emission.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If multiple high power LEDs are connected in series in a compact package, then the desired flux and voltage drop are achieved, but heat dissipation becomes severely limited due to lack of shared thermal path
Solution Approach 1:
The patent divides the thermal management system into multiple independent copper strips, each serving as a separate thermal pathway for individual LED groups. This segmentation allows each LED to have its own dedicated heat sink path, eliminating the bottleneck of shared thermal paths in series-connected LED packages.
Solution Approach 2:
The copper strips serve dual functions: they act as both electrical interconnects for series/parallel LED configurations and as thermal conduction paths for heat dissipation. This multi-functionality resolves the contradiction by integrating electrical and thermal management into a single structure, allowing multiple LEDs to be connected in series while maintaining effective heat sinking through the same copper strips.
2Power
If multiple high power LEDs are connected in series, then the voltage drop requirement is met, but the thermal design complexity increases since LEDs cannot share a large metal pad
Solution Approach 1:
The copper strips serve dual functions: they act as both electrical interconnects for series/parallel LED configurations and as thermal conduction paths for heat dissipation. This multi-functionality resolves the contradiction by integrating electrical and thermal management into a single structure, allowing multiple LEDs to be connected in series while maintaining effective heat sinking through the same copper strips.
Solution Approach 2:
The patent merges the electrical connection function and thermal management function into a single integrated copper strip structure. By combining these functions, the design simplifies the overall thermal management system while maintaining the required electrical connectivity for series-connected LEDs, thereby reducing thermal design complexity.
3Ease of manufacture
If a common submount and PCB are used for multiple LEDs, then manufacturing is simplified, but heat sinking efficiency is reduced compared to direct metal heat sink coupling
Solution Approach 1:
The patent uses copper strips with high thermal and electrical conductivity as an intermediate component between the LED dies and the final heat sink. This composite approach combines the manufacturing simplicity of standardized LED mounting with the superior heat sinking of direct metal coupling, as the copper strips can be easily fabricated and attached while providing excellent thermal pathways.
Solution Approach 2:
The copper strips act as intermediary elements that bridge the gap between the LED dies and the heat sink. These intermediaries provide both electrical connectivity and thermal management, allowing the system to achieve direct heat sink coupling efficiency while maintaining manufacturing simplicity through standardized copper strip fabrication and attachment processes.
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 solution provides efficient heat sinking and wide-angle light emission, suitable for automotive applications, with improved reliability and reduced part count, allowing for effective cooling and uniform temperature distribution across the LED module.
Implementation Method 1
Each of the LED dies has a bottom metal pad which serves as a cathode and a thermal conductor
Implementation Method 2
The three LED dies in a first group have their bottom pads directly soldered or silver-epoxied to a common first copper strip... All the copper strips have a reflective silver layer for reflectance
Implementation Method 3
All the copper strips have a reflective silver layer for reflectance
Implementation Method 4
A top electrode is a wire bond pad and serves as an anode... The anodes of the LED dies in the first group are wire-bonded to the second copper strip
Implementation Method 5
The three LED dies in a first group have their bottom pads directly soldered or silver-epoxied to a common first copper strip
Implementation Method 6
The three LED dies in a first group have their bottom pads directly soldered or silver-epoxied to a common first copper strip
Data Source
Figure 1~3
Figure 4~7
Figure 8~9
AI summary
In one embodiment, an LED bulb includes a plurality of metal lead frame strips, including at least a first strip, a second strip, and a third strip. First LED dies have their bottom electrodes electrically and thermally connected to a top surface of the first strip. Second LED dies have their bottom electrodes electrically and thermally connected to a top surface of the second strip. The top electrodes of the first LED dies are wire bonded to the second strip, and the top electrodes of the second LED dies are wire bonded to the third strip to connect the first LED dies and second LED dies in series and parallel. The strips are then bent to cause the LED dies to face different directions to obtain a wide emission pattern in a small space. The strips are then enclosed in a thermally conductive bulb having electrical leads.