Strip LED Packaging Trench for Gold Wire Thermal Fatigue
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Solution Overview
Problem
Linear LEDs with multiple chips fail to meet stringent automobile specifications due to thermal stress on gold wires caused by mismatched coefficients of linear thermal expansion between the packaging colloid and gold wires, leading to thermal fatigue and breakage during cold and hot temperature cycles.
Innovation Solution
Incorporating a horizontal trench in the packaging colloid with a narrow width between adjacent LED chips to reduce the effective length of thermal stress on electrical connection wires, thereby reducing thermal fatigue and improving reliability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If epoxy or phenyl silicone is used as packaging colloid to maintain structural integrity, then the LED package has sufficient mechanical strength, but thermal stress on gold wires increases during temperature cycles causing reliability degradation
Solution Approach 1:
The packaging colloid is segmented by introducing horizontal trenches that divide the continuous colloid into separate regions. This segmentation reduces the effective length of colloid in contact with gold wires, thereby reducing thermal stress while maintaining local mechanical support where needed.
Solution Approach 2:
The colloid structure is made non-uniform by adding horizontal trenches at specific locations between LED chips. This creates local variations in colloid continuity, reducing thermal stress in critical areas (where gold wires are located) while maintaining structural integrity in other areas.
2Use of energy by moving object
If multiple LED chips are arranged in a row to create linear LED, then light output is enhanced, but thermal stress on electrical connection wires increases leading to thermal fatigue
Solution Approach 1:
Horizontal trenches are introduced to segment the packaging colloid into multiple regions along the linear arrangement of LED chips. This segmentation reduces the continuous thermal stress path on electrical connection wires while maintaining the linear light output configuration.
Solution Approach 2:
The horizontal trenches act as intermediary structures that interrupt the direct thermal stress transmission from the packaging colloid to the electrical connection wires, reducing thermal fatigue without affecting light output.
3Reliability
If packaging colloid with high Tg temperature is used to reduce CLTE mismatch, then thermal stress difference between colloid and gold wire is reduced, but manufacturing complexity increases
Solution Approach 1:
Instead of requiring specialized high-Tg materials, the invention uses standard packaging colloids with horizontal trenches to achieve similar thermal stress reduction effects, simplifying material selection and manufacturing processes.
Solution Approach 2:
The invention changes the structural parameter of the packaging colloid (adding horizontal trenches) rather than changing material parameters (requiring high-Tg materials), thereby achieving thermal stress reduction without increasing manufacturing complexity.
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 horizontal trench design effectively reduces thermal stress on gold wires, enhancing the LED's ability to withstand cold and hot shocks, ensuring compliance with automobile specifications and maintaining uniform light emission without bright spots or dark areas.
Implementation Method 1
A coefficient of linear thermal expansion (CLTE) of epoxy is about 20-40 ppm/° C. below a glass transition temperature (Tg), but when the temperature exceeds the glass transition temperature (Tg), the CLTE of epoxy rises rapidly by about 3-4 times, which is much larger than a CLTE of a gold wire (about 14 ppm/° C.).
Data Source
AI summary
A strip-shaped light-emitting diode (LED) and an application device are provided. The strip-shaped LED includes a substrate, a plurality of LED chips, a plurality of electrical connection wires connected to electrodes of the LED chips, and a packaging colloid. The plurality of LED chips are linearly arranged, covered by the packaging colloid, and the packaging colloid has a horizontal fine trench between two specified adjacent LED chips. Reliability of resistance to cold and hot temperature cycles or cold and hot shocks can be improved.