LED Filament with Flexible Substrate for Uniform Illumination
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Solution Overview
Problem
LED light bulbs with traditional hard or soft filaments face challenges in achieving uniform illumination due to substrate blocking light, thermal expansion issues, stress concentration leading to metal wire breakage, and complex assembly processes, along with inefficient heat dissipation and flicker in power supply.
Innovation Solution
An LED filament using a Polyimide film substrate with copper foil and silver plating, where copper foil is placed between LED chips, and conductive electrodes are connected with wires, covered by a light conversion layer, and a power supply module with a rectifying, filtering, and driving circuit to provide stable current, enhancing heat dissipation and light emission efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If a glass substrate is used in LED hard filament, then structural stability is improved, but light transmission is blocked and illumination uniformity deteriorates
Solution Approach 1:
The patent replaces the traditional glass substrate with a flexible printed circuit board (FPC) substrate. This thin film approach allows the substrate to be flexible and transparent, enabling uniform light transmission while maintaining structural stability through the circuit board design. The FPC substrate can be bent to create curved LED filament shapes without breaking, while still providing mechanical support and electrical connectivity.
Solution Approach 2:
The patent employs a composite structure combining FPC substrate with LED chips, phosphor materials, and encapsulant resin. This composite approach integrates the mechanical support function of the substrate with the light-emitting function of LED chips and the light-diffusing function of phosphor, achieving both structural stability and uniform illumination simultaneously.
2Adaptability or versatility
If FPC substrate is used in LED soft filament, then flexibility and bending capability are improved, but thermal expansion mismatch causes LED chip displacement and metal wire bonding damage
Solution Approach 1:
The patent carefully selects FPC substrate materials with thermal expansion coefficients matched to LED chips and encapsulant resin. By controlling the thermal expansion parameter of the substrate material, the patent prevents relative displacement between LED chips and substrate during temperature changes, while maintaining the flexibility and bending capability of the FPC structure.
Solution Approach 2:
The patent designs the FPC substrate with appropriate thickness and structural reinforcement in advance to prevent excessive bending stress concentration. This beforehand cushioning approach ensures that when the LED filament is bent, the stress is distributed evenly throughout the substrate, preventing metal wire bonding damage and LED chip displacement while maintaining flexibility.
3Illumination intensity
If multiple LED filaments are installed in a single LED light bulb, then illumination uniformity is improved, but assembly complexity and production cost increase
Solution Approach 1:
The patent merges multiple LED chip units onto a single FPC substrate to form one integrated LED filament. This combining approach allows the filament to provide uniform illumination equivalent to multiple separate filaments while being installed as a single component, greatly simplifying the assembly process and reducing production complexity.
Solution Approach 2:
The patent arranges LED chips in a two-dimensional array pattern on the FPC substrate rather than a single linear row. This dimensional change allows light to be emitted from multiple points across the filament surface, achieving uniform illumination distribution while maintaining a single-filament structure that is easy to install.
4Illumination intensity
If LED chips are arranged densely on the filament, then light emission intensity is improved, but stress concentration during bending causes metal wire bonding breakage
Solution Approach 1:
The patent designs the FPC substrate with increased thickness and structural reinforcement at the locations where metal wire bonding connects adjacent LED chips. This beforehand cushioning provides extra mechanical strength at stress concentration points, preventing wire bonding breakage even when LED chips are arranged densely and the filament is bent into curves.
Solution Approach 2:
The patent uses a composite encapsulant resin structure that surrounds and protects the metal wire bonding between densely arranged LED chips. This composite material approach provides both mechanical protection to prevent wire breakage and proper spacing to allow heat dissipation, enabling dense chip arrangement without compromising wire bonding strength.
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 improves thermal radiation, reduces the probability of conductive wire breakage, enhances luminous efficiency, achieves uniform and wide illumination, and provides a stable current to prevent flicker, resulting in a reliable and efficient LED light bulb.
Implementation Method 1
copper foil and at least one LED chip are attached on the LED filament substrate, wherein the copper foil is located between two adjacent LED chips
Implementation Method 2
a first light conversion layer covers a single LED chip and part of a first wire and a second wire which are connected with the LED chip
Data Source
Figure 1A~2
Figure 3A~3C
Figure 3D~3F
AI summary
An LED filament (100) comprises at least one LED section (102, 104), a conductive section (130), two conductive electrodes (110, 112) and a light conversion layer (120). The conductive section (130) is used to electrically connect two adjacent LED sections (102, 104). The two conductive electrodes (110, 112) are electrically connected to each of the LED sections (102, 104). Each of the LED sections (102, 104) includes at least two LED chips (142) electrically connected to each other. The light conversion layer (120) covers the LED sections (102, 104), the conductive sections (130) and the conductive electrodes (110, 112), and a part of the two electrodes (110, 112) is exposed respectively. Since the LED filament (100) includes the LED section (102, 104) and the conductive section (130), when the LED filament (100) is bent, the stress is easily concentrated on the conductive section (130). Therefore, the breakage probability of the conductive wires (140) connected within the LED section (102, 104) is reduced during bending.The quality of the LED flament (100) and its application is improved.