Leadframe-Based Packages for Solid State Light Emitting Devices
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Solution Overview
Problem
Existing solid state light emitting device packages face challenges in heat dissipation and thermal performance, particularly when multiple LEDs are mounted closely together for applications like general lighting, where heat retention limits the intensity and color of combined light emission.
Innovation Solution
A modular package design featuring a leadframe with a central region and electrical leads of varying thicknesses, where the central region has a thicker bottom surface and oblique sidewalls forming a reflector cup, allowing for improved heat dissipation through a larger surface area rather than the leads, and an encapsulant forming a lens above the reflector cup for optical enhancement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If heat is extracted through the leads in conventional packages, then electrical connection is maintained, but thermal resistance increases and limits heat dissipation
Solution Approach 1:
The patent transitions from one-dimensional heat extraction through narrow leads to two-dimensional heat dissipation through the bottom surface of the central region. The leadframe's bottom surface provides a large area contact with the heatsink, enabling heat to be extracted across a broad surface rather than through constrained lead paths, thereby reducing thermal resistance while maintaining electrical connection integrity.
2Illumination intensity
If multiple LEDs are mounted closely together, then light intensity and color mixing improve, but heat retention increases
Solution Approach 1:
The leadframe is divided into distinct functional regions: a central region for mounting multiple LEDs in close proximity to achieve desired light output, and a bottom surface region optimized for heat extraction. This segmentation allows the lighting function and thermal management function to be optimized independently, enabling high-intensity multi-LED configurations without suffering from heat retention issues.
3Temperature
If the leadframe central region has uniform thickness, then manufacturing is simplified, but heat dissipation surface area is reduced
Solution Approach 1:
The leadframe exhibits local quality variations in its thickness profile: the central region maintains a first thickness optimized for LED mounting and electrical connection, while the bottom surface extends to a second, greater thickness to maximize heat dissipation surface area. This localized thickness variation is achieved through stamping processes that create the desired profile, balancing manufacturing feasibility with optimized thermal performance.
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 enhances thermal performance by reducing thermal resistance and improving heat dissipation, enabling higher intensity and better color mixing of light emitted by multiple LEDs, while maintaining optical quality and simplifying assembly through injection molding techniques.
Implementation Method 1
improved heat dissipation through a larger surface area rather than the leads
Implementation Method 2
reducing thermal resistance and improving heat dissipation
Implementation Method 3
The reflective cup 13 may be filled with an encapsulant material 16 containing a wavelength conversion material such as a phosphor. Light emitted by the LED at a first wavelength may be absorbed by the phosphor, which may responsively emit light at a second wavelength.
Implementation Method 4
The entire assembly is then encapsulated in a clear protective resin 14, which may be molded in the shape of a lens to collimate the light emitted from the LED chip 12.
Implementation Method 5
The upper sidewalls may include oblique inner surfaces that define a reflector cup surrounding the die mounting region.
Data Source
AI summary
A modular package for a light emitting device includes a leadframe having a top surface and including a central region having a bottom surface and having a first thickness between the top surface of the leadframe and the bottom surface of the central region. The leadframe may further include an electrical lead extending away from the central region. The electrical lead has a bottom surface and has a second thickness from the top surface of the leadframe to the bottom surface of the electrical lead. The second thickness may be less than the first thickness. The package further includes a package body on the leadframe surrounding the central region and exposing the bottom surface of the central region. The package body may be at least partially provided beneath the bottom surface of the lead and adjacent the bottom surface of the central region. Methods of forming modular packages and leadframes are also disclosed.