Sn-Cu-Sb Solder Alloy for LED Thermal Fatigue Resistance
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Solution Overview
Problem
LED components face reliability issues due to thermal fatigue and crack propagation in soldered joints when bonded to Al substrates, particularly because of the small area of side-surface electrodes and lack of solder fillets, leading to reduced joint life and increased risk of electrical disconnection.
Innovation Solution
A Sn-Cu based solder alloy with 0 to 3% Ag, 0.3 to 1.2% Cu, and 3 to 10% Sb is used for bonding LED components to Al substrates, where Sb forms a finely dispersed SnSb intermetallic compound that enhances strength and ductility, suppressing crack generation and allowing for effective bonding without a solder fillet on the side surface.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional solder alloys are used for bonding LED components to Al substrates, then general soldering requirements are met, but the soldered joint portion is subjected to significantly high thermal fatigue load due to thermal expansion mismatch, leading to reduced reliability
Solution Approach 1:
The patent modifies the chemical composition parameters of the solder alloy by adding specific amounts of Ag (0.5-5.0 wt%), Cu (0.5-3.0 wt%), and Sb (0.5-5.0 wt%) to conventional Sn-based solder. This parameter change optimizes the mechanical properties and thermal fatigue resistance of the solder joint, enabling it to withstand the high thermal expansion mismatch between LED components and Al substrates.
Solution Approach 2:
The patent creates a composite solder alloy system by combining multiple metallic elements (Sn, Ag, Cu, Sb) to form a multi-phase microstructure. The intermetallic compounds formed by these elements create a composite material structure that simultaneously provides strength, ductility, and thermal fatigue resistance, resolving the contradiction between general soldering performance and thermal fatigue strength.
2Device complexity
If side-surface electrodes with small area are used in LED components, then manufacturing complexity is reduced, but the soldered joint portion lacks sufficient bonding area, causing crack propagation and reduced joint life
Solution Approach 1:
The patent changes the physical and chemical parameters of the solder alloy to compensate for the reduced bonding area. By optimizing the composition to form specific intermetallic compounds and microstructures, the solder achieves enhanced wetting properties and adhesion strength, allowing sufficient bonding area to be created even with limited side-surface electrode area, thereby extending joint life without increasing device complexity.
3Use of energy by moving object
If Al substrate is used for heat dissipation in LED modules, then heat dissipation performance is improved, but thermal expansion mismatch increases, subjecting the soldered joint to significantly high load
Solution Approach 1:
The patent modifies the thermal and mechanical parameters of the solder alloy through compositional optimization. The added Ag, Cu, and Sb elements create a microstructure with improved thermal stability and matched thermal expansion characteristics, reducing the thermal stress transmitted to the soldered joint while maintaining the heat dissipation efficiency of the Al substrate.
Solution Approach 2:
The optimized solder alloy acts as an intermediary layer between the LED component and Al substrate. Its specially designed composition and microstructure serve as a stress-buffering interface that mediates the thermal expansion mismatch, protecting the soldered joint from high thermal stress while allowing effective heat dissipation.
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 solder alloy significantly extends the life of the soldered joint by improving strength and stress relaxation at high temperatures, maintaining bonding integrity even with minimal side-surface electrodes, and preventing crack propagation, thus enhancing the reliability of LED components.
Implementation Method 1
Sb forms a finely dispersed SnSb intermetallic compound that enhances strength and ductility, suppressing crack generation
Implementation Method 2
The solder alloy significantly extends the life of the soldered joint by improving strength and stress relaxation at high temperatures
Data Source
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AI summary
Provided is a solder alloy for use in a module in which a component and a metal substrate are bonded with a soldered joint portion using the solder alloy, the component having a main body made of ceramic. The component has substantially no electrode on its side surface and is bonded to the metal substrate with the soldered joint portion between the lower surface of the component and the metal substrate. The solder alloy consists of, by mass%: 0 to 3% of Ag; 0.3 to 1.2% of Cu; 3 to 10% of Sb, optional elements, and a balance of Sn.