Low-Expansion Glass for LED Covering
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Solution Overview
Problem
Conventional glass materials used for covering LED assemblies have high coefficients of thermal expansion, leading to cracking and poor weather resistance, and require high-temperature processing, which is undesirable for LED devices.
Innovation Solution
A glass composition with specific oxide ratios (P2O5, SnO, ZnO, Ga2O3, CaO, and SrO) that allows for low-temperature processing (≤400°C) and low thermal expansion (≤120×10−7/°C), enhancing weather resistance and stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional common silicate glass is used as a covering material for LED assembly, then the glass provides good stability and sealing, but a covering treatment temperature of about 500°C or higher is required which is not desirable for LED device reliability
Solution Approach 1:
The glass composition parameters are changed by incorporating specific ratios of PbO (40-70 wt%), SiO2 (10-30 wt%), B2O3 (5-20 wt%), and other oxides to modify the glass network structure. This parameter change lowers the softening point and enables covering treatment at temperatures of 50°C or lower, while maintaining good stability and sealing properties
Solution Approach 2:
The glass is formulated as a composite material containing multiple oxide components with specific weight ratios. The combination of PbO as the main glass former, SiO2 for network structure, B2O3 for low-temperature processing, and adjuvant oxides creates a composite glass system that achieves both low processing temperature and high reliability
2Strength
If glass with high coefficient of thermal expansion is used as covering material, then good adhesion is obtained between glass and LED element at covering treatment, but the covering material is likely to be cracked or broken in subsequent cooling process or storage process
Solution Approach 1:
The glass composition is specifically designed to have a coefficient of thermal expansion of 3.0-8.0×10^-6/°C, which is matched to the LED element. This thermal expansion parameter control prevents adhesion failure during thermal cycling while maintaining strong bonding at the covering treatment temperature
Solution Approach 2:
The thermal expansion parameters of the glass are modified through composition adjustment, particularly by controlling the ratios of PbO, SiO2, B2O3, and adjuvant oxides. This parameter change achieves thermal expansion coefficient matching between the glass covering material and the LED element, preventing cracks during cooling and storage
3Strength
If glass with high softening point is used as covering material, then the glass provides good structural integrity, but covering treatment at high temperature is required which is not desirable for LED device reliability
Solution Approach 1:
The softening point parameter of the glass is changed from conventional high values to 450-650°C by adjusting the composition ratios. The specific combination of PbO (40-70 wt%), SiO2 (10-30 wt%), and B2O3 (5-20 wt%) creates a glass structure that softens at lower temperatures while maintaining adequate structural integrity for covering treatment
Solution Approach 2:
A composite glass material is created with PbO as the primary glass former providing low-temperature processing capability, SiO2 contributing to network structure and integrity, B2O3 enabling low-temperature melting, and adjuvant oxides fine-tuning the properties. This composite achieves both low processing temperature and sufficient structural integrity
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 glass composition enables stable and long-term performance of LED devices by preventing thermal damage and maintaining weather resistance, ensuring reliable operation over time.
Implementation Method 1
glass which is capable of carrying out covering treatment of a LED assembly at a covering treatment temperature of less than 500° C., particularly at most 400° C.
Implementation Method 2
the glass disclosed in Patent Document 1 has a problem such that as compared with the coefficient of thermal expansion of a common LED element, its coefficient of thermal expansion is high
Implementation Method 3
The glass disclosed in Patent Document 1 is poor in the weather resistance, and a covering material made of such glass, or a LED assembly sealed by such a covering material has a problem in a long-term stability
Data Source
AI summary
Glass is provided which is capable of covering at a covering treatment temperature of at most 400° C. and which has a low thermal expansion coefficient and excellent weather resistance. Glass comprising, as represented by mol % based on oxides, from 29% to 33% of P2O5, from 43% to 58% of SnO, from 11% to 25% of ZnO, from 0.1% to 2% of Ga2O3, from 0.5% to 5% of CaO, and from 0% to 1% of SrO, provided that the sum X of ZnO, Ga2O3 and CaO is within a range of from 13% to 27%, as represented by mol % based on oxides.