LED Sub-Mount Solder Bond Slit Design for Thermal Strain
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Solution Overview
Problem
High-output light emitting devices, such as LEDs, face challenges in thermal management due to thermal expansion coefficient differences between sub-mounts and main-mounts, leading to strain and inclination issues during thermal cycling tests, which can result in solder bond failures.
Innovation Solution
A light emitting device design featuring a sub-mount with back surface electrodes and a main-mount with a front surface metal pattern that includes slits and necked portions to reduce thermal strain and prevent inclination, along with a solder bond structure that balances solder thickness and distribution to maintain even contact.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the back surface electrode of the sub-mount and the electrode pad of the main-mount are connected using solder in a solder reflow process, then electrical connection is achieved, but the sub-mount may become inclined with respect to the main-mount
Solution Approach 1:
The back surface electrode is divided into two separate electrodes rather than being a single continuous structure. This segmentation allows independent positioning and soldering of each electrode to the main-mount, enabling better control over the sub-mount's orientation and preventing inclination while maintaining electrical connections.
2Temperature
If thermal expansion coefficient difference between the sub-mount and the main-mount is large, then thermal management is achieved, but damage due to strain may occur in a thermal cycling test
Solution Approach 1:
Dividing the back surface electrode into two separate electrodes creates independent thermal expansion paths. Each electrode can expand and contract independently during thermal cycling, reducing the cumulative strain on the solder joints and preventing damage while maintaining effective heat dissipation from the light emitting element.
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 enhances strain resistance during thermal cycles and prevents inclination of the sub-mount relative to the main-mount, improving the reliability and durability of the solder bond structure.
Implementation Method 1
a wiring electrode bonded to the back surface electrode via solder
Implementation Method 2
part of the heat generated by the light emitting element can be dissipated to the main-mount via the back surface electrodes formed in the sub-mount and the electrode pads formed in the main-mount
Data Source
AI summary
A light emitting device includes a light emitting element; a sub-mount including a sub-mount substrate with a front surface on which the light emitting element is disposed, and a back surface electrode disposed in a back surface that is on a back side of the front surface of the sub-mount substrate; a main-mount in which the sub-mount is disposed, the main-mount including a front surface metal pattern including a wiring electrode bonded to the back surface electrode via solder. The front surface metal pattern has a slit, in a plan view, at a position away from a disposition region in which the sub-mount is disposed.