Composite LED Substrate Thermal Expansion Mismatch
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing LED substrates face challenges with thermal conductivity and coefficient of linear thermal expansion mismatch with III-V semiconductor crystals, leading to warping, cracking, and reduced light emission efficiency, especially in high-output LEDs.
Innovation Solution
A composite material substrate is developed by infiltrating porous bodies with aluminum alloy or pure aluminum at high pressure, combined with a metal layer, to achieve high thermal conductivity and a coefficient of linear thermal expansion close to III-V semiconductor crystals, while also providing chemical resistance and electroconductivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a monocrystalline sapphire substrate is used for epitaxial growth of III-V semiconductor crystals, then good single crystal growth can be achieved, but the difference in coefficient of linear thermal expansion causes warping and cracking of the substrate
Solution Approach 1:
The patent employs a composite substrate structure consisting of a sapphire substrate with a bonded high-thermal-conductivity layer (such as diamond or copper). This composite structure allows the sapphire to provide excellent crystalline properties for epitaxial growth while the additional layer compensates for thermal expansion mismatch and improves thermal management, preventing warping and cracking.
Solution Approach 2:
The patent modifies the thermal and mechanical parameters of the substrate system by bonding an additional layer with specific thermal conductivity and thermal expansion properties. This changes the overall thermal management characteristics of the substrate, enabling it to withstand the thermal stresses generated during LED operation without warping or cracking.
2Manufacturing precision
If a monocrystalline sapphire substrate is used, then epitaxial growth can proceed, but the poor thermal conductivity (about 40 W/mK) is insufficient to dissipate heat from high-output LEDs
Solution Approach 1:
The patent creates a composite substrate by bonding a high-thermal-conductivity material (such as diamond with thermal conductivity >1000 W/mK or copper with thermal conductivity >400 W/mK) to the sapphire substrate. This composite structure maintains the sapphire's excellent epitaxial growth properties while adding superior heat dissipation capability through the high-conductivity layer.
Solution Approach 2:
The substrate function is segmented into two distinct layers: the sapphire layer responsible for providing a crystalline template for epitaxial growth, and a separate high-thermal-conductivity layer dedicated to heat dissipation. This segmentation allows each layer to optimize its specific function without compromising the other.
3Temperature
If copper is used as a high thermal conductivity substrate, then thermal conductivity is improved, but the coefficient of linear thermal expansion differs greatly from III-V semiconductor crystals
Solution Approach 1:
The patent uses a composite structure where copper (or other high-conductivity materials) is bonded to sapphire. The sapphire layer acts as an intermediate that is compatible with both the III-V semiconductor crystals and the copper layer, mediating the thermal expansion mismatch. This allows the system to achieve high thermal conductivity from the copper while maintaining compatibility with the semiconductor through the sapphire interface.
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 composite substrate enhances heat dissipation, reliability, and light emission efficiency of high-output LEDs, simplifies production processes, and increases light emission per unit area by matching thermal expansion coefficients and providing adequate strength and chemical resistance.
Implementation Method 1
infiltrating, with an aluminum alloy or pure aluminum, at an infiltrating pressure of at least 30MPa, a plurality of porous bodies stacked in a stacking block that is heated at a temperature of 600 to 800°C
Implementation Method 2
heated at a temperature of 600 to 800°C
Implementation Method 3
excelling in thermal conductivity
Implementation Method 4
forming, on a surface, a metal layer comprising one or more metals chosen from among Ni, Co, Pd, Cu, Ag, Pt and Sn
Data Source
Figure 1~3
AI summary
A substrate for an LED light emitting element having a small difference of linear thermal expansion coefficient with the III-V semiconductor crystal constituting an LED, having an excellent thermal conductivity and suitable for high output LEDs. A porous body comprises one or more materials selected from silicon carbide, aluminum nitride, silicon nitride, diamond, graphite, yttrium oxide, and magnesium oxide and has a porosity that is 10 to 50 volume % and a three-point bending strength that is 50 MPa or more. The porous body is infiltrated, by means of liquid metal forging, with aluminum alloy or pure aluminum at an infiltration pressure of 30 MPa or more, cut and/or ground to a thickness of 0.05 to 0.5 mm and to a surface roughness (Ra) of 0.01 to 0.5 µm, then is formed with a metal layer comprising one or more elements selected from Ni, Co, Pd, Cu, Ag, Au, Pt and Sn on its surface to a thickness of 0.5 to 15 µm, so as to thereby produce the composite substrate for the LED light emitting element.