LED Filament Thermal Expansion Mismatch and Wire Bond Stress
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Solution Overview
Problem
LED soft filaments with flexible printed circuit substrates face issues such as thermal expansion mismatch, degradation of LED chips, stress on metal wire bonds, complex assembly processes, and challenges in designing power supply circuits for stable current and reduced ripple phenomena.
Innovation Solution
The design incorporates an LED filament with conductive sections and electrodes, where LED sections are connected by conductive wires, and a light conversion layer covers the structure, using an organosilicon-modified polyimide composition for the substrate or light-conversion layer, which includes a thermal curing agent and heat dispersing particles to enhance flexibility and thermal conductivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If FPC substrate is used for LED soft filament to enable bending flexibility, then flexibility is improved, but thermal expansion mismatch causes LED chip displacement and degumming
Solution Approach 1:
The patent changes the thermal expansion parameter by selecting a substrate material (PET or PI) whose thermal expansion coefficient matches that of the LED chip and silver paste, eliminating thermal expansion mismatch during temperature cycles and preventing LED chip displacement and degumming
Solution Approach 2:
The patent uses composite material structure with specific layer combinations (substrate, reflective layer, conductive layer, LED chip, protective layer) where each layer is selected for its specific properties, creating a composite structure that provides both flexibility and thermal stability
2Productivity
If metal wire bonding is used to connect adjacent LED chips in dense arrangement, then electrical connection is achieved, but stress concentration during bending damages wire bonds
Solution Approach 1:
The patent extracts the vulnerable metal wire bonding from the bending stress path by using a rigid substrate that prevents bending, thereby eliminating the stress concentration that causes wire bond damage while maintaining LED chip density through alternative connection methods
Solution Approach 2:
The patent provides beforehand protection by selecting a rigid substrate material that prevents bending before it occurs, thereby preventing stress concentration and protecting the wire bonds from damage before any bending stress can be applied
3Illumination intensity
If multiple LED filaments are installed with different placements and angles for aesthetic appearance, then illumination uniformity is improved, but assembly process becomes complicated
Solution Approach 1:
The patent segments the lighting function into multiple independent LED filaments that can be individually designed with different placements and angles, allowing each segment to contribute to overall illumination uniformity while maintaining independent assembly characteristics
Solution Approach 2:
The patent creates a universal base structure (socket, mounting mechanism) that accommodates multiple LED filaments with different orientations, providing a standardized interface that simplifies assembly despite the varied configurations needed for optimal illumination
4Device complexity
If conventional power supply circuit is used for LED filament, then circuit design is simple, but current instability and ripple phenomena occur
Solution Approach 1:
The patent introduces intermediary components (capacitors, inductors, or active regulation circuits) between the power source and LED filament that filter and stabilize the current, reducing ripple phenomena while maintaining relatively simple overall circuit design through modular power management
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 reduces the breakage of metal wire bonds during bending, simplifies assembly, and achieves stable current supply with reduced ripple, while providing improved thermal dissipation and light efficiency.
Implementation Method 1
which includes a thermal curing agent
Implementation Method 2
heat dispersing particles to enhance flexibility and thermal conductivity
Implementation Method 3
LED sections are connected by conductive wires, and a light conversion layer covers the structure
Data Source
AI summary
An high-efficiency light bulb, comprising: a lamp housing with inner surface and outer surface opposite to the inner surface of the lamp housing, the lamp housing includes a layer of luminescent material, which is formed on the inner surface or the outer surface of the lamp housing or integrated in the material of the lamp housing; a bulb base connected to the lamp housing; a stem connected to the bulb base and located in the lamp housing; and a single filament, disposed in the light housing, further comprising a plurality of supporting arms, connected with and supporting the LED filament, wherein the stem comprises a stand extending to the center of the lamp housing, the stand supports the supporting arms.