LED Lead Frame Structure for Flip-Chip Thermal Stress Relief
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Solution Overview
Problem
Conventional LED packages face challenges in achieving high light emission efficiency and uniformity due to light loss and mechanical stress issues, particularly when using flip-chip mounting of LED chips on lead frame structures, which limits their application in compact sizes and thermal cycling reliability.
Innovation Solution
The LED package incorporates a lead frame structure with stress relief features and anchoring features, including notches, trenches, and openings, to enhance mechanical integrity during thermal cycling, along with a housing that forms a recess for LED chip positioning, and uses light-altering materials to optimize light emission direction and efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If multiple LED chips are flip-chip mounted in larger LED packages, then brightness and light emission efficiency increase, but thermal stress and mechanical integrity deteriorate
Solution Approach 1:
The lead frame structure is segmented into multiple leads with distinct mounting locations, allowing separate stress management for each LED chip. Stress relief features are distributed at different locations rather than concentrated, enabling localized stress accommodation while maintaining overall structural integrity across the larger package footprint.
Solution Approach 2:
Different regions of the lead frame structure have different properties: mounting locations have enhanced stress relief features (notches, trenches) for stress accommodation, while other regions maintain structural rigidity for mechanical support. This local differentiation allows the structure to simultaneously handle thermal stress at mounting points and provide overall mechanical strength.
2Reliability
If lead frame structures include stress relief features, then thermal stress is mitigated, but device complexity increases
Solution Approach 1:
Multiple stress relief features (notches and trenches) are merged into a single integrated lead frame structure rather than separate components. The notches and trenches are formed as part of the lead frame manufacturing process, combining stress relief functionality with the structural support function in one unified component.
Solution Approach 2:
The lead frame structure serves multiple functions simultaneously: it provides mechanical support for LED chips, establishes electrical connections through leads, and accommodates thermal stress through integrated notches and trenches. This multi-functionality reduces the need for additional separate components, offsetting the complexity added by stress relief features.
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 configuration enhances the mechanical integrity and light emission efficiency of LED packages, allowing for multiple flip-chip LEDs in larger footprints while maintaining suitable forward driving voltages and reducing thermal stress, thereby improving brightness and reliability.
Implementation Method 1
LEDs are solid-state devices that convert electrical energy to light and generally include one or more active layers of semiconductor material (or an active region) arranged between oppositely doped n-type and p-type layers. When a bias is applied across the doped layers, holes and electrons are injected into the one or more active layers where they recombine to generate emissions such as visible light or ultraviolet emissions.
Implementation Method 2
Lumiphoric materials, such as phosphors, may also be arranged in close proximity to LED emitters to convert portions of light emissions to different wavelengths.
Data Source
AI summary
Light-emitting diode (LED) packages and more particularly LED packages with lead frame structures for flip-chip mounting of LED chips are disclosed. Lead frame structures include multiple leads with arrangements for LED chips to be flip-chip mounted across neighboring pairs of leads. Arrangements of stress relief features and anchoring features relative to mounting locations are provided in lead frame structures to enhance mechanical integrity of flip-chip bonds during thermal cycling. LED packages may further include housings that are formed about the lead frame structures. Housings may include a recess with recess floor arrangements for positioning of LED chips.