Laser Diode Surface Mounting Structure for Thermal Stress Reduction
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Solution Overview
Problem
Conventional laser diode package structures fail to simultaneously achieve high current, high heat dissipation capacity, and low thermal stress, leading to reduced efficiency and lifespan due to thermal stress from mismatched thermal expansion coefficients and inadequate heat dissipation pathways.
Innovation Solution
A surface mounting package structure featuring a heat-dissipating plate with a conductive through hole and thin, thermally conductive materials like aluminum nitride or aluminum oxide, combined with a tin-plated copper metal plate, and symmetrically arranged bonding wires to minimize thermal stress and enhance heat dissipation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the substrate thickness is increased to provide mechanical support, then the mechanical strength is improved, but the heat dissipation capacity deteriorates due to the longer heat conduction path
Solution Approach 1:
The substrate is segmented into a thin substrate layer and a separate heat-dissipating plate structure. The thin substrate (thickness ≤ 50 μm) provides mechanical support, while the heat-dissipating plate with through-holes provides efficient heat conduction path, separating the mechanical support function from the heat dissipation function to resolve the contradiction between mechanical strength and heat dissipation capacity.
Solution Approach 2:
Heat dissipation is enhanced by adding a vertical dimension through through-holes penetrating the heat-dissipating plate. This creates direct thermal conduction pathways from the laser cavity through the substrate to the heat-dissipating plate, reducing the effective heat conduction distance and improving heat dissipation capacity without compromising mechanical strength.
2Temperature
If materials with different coefficients of thermal expansion are used for the substrate and heat-dissipating plate, then the heat dissipation capacity is improved, but thermal stress is generated causing crystal lattice distortion
Solution Approach 1:
A buffer layer is introduced as an intermediary between the substrate and the heat-dissipating plate. This buffer layer has a coefficient of thermal expansion intermediate between the substrate and the heat-dissipating plate, gradually transitioning the thermal expansion mismatch and reducing thermal stress while maintaining effective heat dissipation pathways.
Solution Approach 2:
The heat-dissipating plate is designed as a composite structure with through-holes filled with high-thermal-conductivity materials. This composite structure provides both efficient heat dissipation and controlled thermal expansion characteristics, allowing the system to achieve good thermal contact while managing thermal stress through the composite material properties.
3Reliability
If soft materials like indium or silver glue are interposed between the epitaxial layer and heat-dissipating plate to avoid thermal stress, then thermal stress is reduced, but electrical conductivity and heat dissipation capacity deteriorate
Solution Approach 1:
The soft material layer is completely removed from the thermal conduction path between the epitaxial layer and the heat-dissipating plate. Instead, direct thermal and electrical contact is established through the thin substrate and the through-hole structure, extracting the problematic soft material layer that caused both thermal stress and electrical resistance issues.
Solution Approach 2:
The thin substrate (thickness ≤ 50 μm) acts as a flexible thin film that provides both mechanical support and direct thermal/electrical conduction pathways. This thin film structure eliminates the need for soft material interlayers while maintaining thermal stress management through its flexibility and direct contact with the heat-dissipating plate.
4Device complexity
If bonding wires are arranged asymmetrically to connect electrodes, then the electrical connection is simplified, but thermal stress is generated due to asymmetric heat dissipation
Solution Approach 1:
The bonding wires are arranged symmetrically with respect to the laser cavity and heat-dissipating plate structure. This symmetric arrangement ensures that heat is dissipated uniformly through the through-holes and bonding wire connections, preventing asymmetric thermal expansion and thermal stress while maintaining simple electrical connectivity between the electrodes.
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 enables efficient heat dissipation and high current handling while minimizing thermal stress, thereby maintaining high emission efficiency and extending the lifespan of the laser diode.
Implementation Method 1
The heat-dissipating plate for carrying one of the two electrodes of the at least one edge-emitting laser diode chip
Implementation Method 2
at least one conductive through hole extending from the top conductive layer to the bottom conductive layer for electrical conduction
Implementation Method 3
thin, thermally conductive materials like aluminum nitride or aluminum oxide
Implementation Method 4
tin-plated copper metal plate
Implementation Method 5
tin-plated copper metal plate
Implementation Method 6
the second metal plate is electrically connected, via at least one bonding wire, to the other electrode
Data Source
AI summary
A laser diode surface mounting structure, having at least one edge-emitting laser diode chip, including two electrodes; a heat-dissipating plate for carrying one of the two electrodes of the at least one edge-emitting laser diode chip, which has a top conductive layer, a bottom conductive layer, and at least one conductive through hole extending from the top conductive layer to the bottom conductive layer for electrically conducting; two or more metal plates spaced apart from each other and located on a plane, wherein a first metal plate is located under the heat-dissipating plate and in contact with the bottom conductive layer of the heat-dissipating plate, and a second metal plate is located adjacent to and separated from the first metal plate; and an insulating frame having an opening and being disposed above the two or more metal plates for holding the two or more metal plates.