Sn-Ag-Cu Solder Alloy Composition for Thermal Fatigue Resistance
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing solder alloys lack sufficient durability, crack resistance, erosion resistance, and tend to form voids, particularly requiring improvement in cold thermal fatigue and melting point management for electronic circuit applications.
Innovation Solution
A tin-silver-copper solder alloy with specific compositions of nickel, cobalt, bismuth, indium, and antimony, optimized in mass ratios and content ranges to achieve low melting points, enhanced mechanical characteristics, and reduced void formation, used in solder pastes for electronic circuit boards.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional lead-free solder alloys are used, then environmental burden is reduced, but durability and cold thermal fatigue resistance are insufficient
Solution Approach 1:
The patent applies parameter changes by precisely controlling the compositional parameters of the solder alloy. Specifically, it maintains Ag content at 2.0-4.0 mass%, Cu at 0.1-1.0 mass%, and adds Bi at 0.1-6.0 mass%, In at 0.1-6.0 mass%, and Ge at 0.003-0.03 mass%. These parameter adjustments optimize the microstructure and mechanical properties, significantly improving durability and cold thermal fatigue resistance while maintaining lead-free composition.
Solution Approach 2:
The patent creates a composite material system by combining multiple elements (Sn-Ag-Cu-Bi-In-Ge) to achieve synergistic effects. The base Sn-Ag-Cu alloy is enhanced with Bi for low melting point and improved strength, In for ductility and crack resistance, and Ge for oxidation resistance and microstructure control. This multi-element composite approach resolves the contradiction by integrating the benefits of each element to simultaneously improve durability and thermal fatigue resistance.
2Strength
If solder alloy composition is optimized for strength, then mechanical characteristics improve, but melting point increases
Solution Approach 1:
The patent uses parameter changes to decouple the relationship between strength and melting point. By adding Bi (0.1-6.0 mass%) and In (0.1-6.0 mass%) to the Sn-Ag-Cu base alloy, the melting point is suppressed through eutectic reactions, while the mechanical strength is maintained or improved through microstructure refinement and intermetallic compound formation. The Ge content (0.003-0.03 mass%) further optimizes the microstructure without significantly affecting the melting point.
Solution Approach 2:
The patent exploits phase transitions by utilizing the eutectic reactions of Bi-Sn and In-Sn systems. The addition of Bi and In creates low-melting-point eutectic phases that lower the overall melting point of the alloy. Simultaneously, these elements form strengthening intermetallic compounds (such as Ag3Sn, Cu6Sn5, and Bi2Te3) during solidification, which enhance mechanical strength. This phase transition mechanism allows the alloy to achieve both low melting point and high strength.
3Reliability
If solder alloy is used for electronic circuits, then electrical connectivity is achieved, but void formation and erosion reduce reliability
Solution Approach 1:
The patent applies parameter changes to suppress void formation and erosion. The Ge content is precisely controlled at 0.003-0.03 mass%, which is sufficient to form a protective oxide layer on the solder surface that prevents erosion, while not excessive to cause brittleness. The Bi and In content ranges (0.1-6.0 mass% each) are optimized to control solidification behavior and reduce void formation by promoting uniform distribution of intermetallic compounds and reducing gas entrapment during soldering.
Solution Approach 2:
The patent uses Ge as an intermediary element that forms a protective oxide layer (GeO2) on the solder surface. This oxide layer acts as a barrier that prevents oxidation of the underlying Sn, Ag, and Cu elements, thereby reducing erosion. Additionally, Bi and In serve as intermediaries during the soldering process, modifying the wetting behavior and solidification pattern to reduce void formation. These intermediary elements mediate between the solder alloy and the environment, protecting the joint 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 optimized solder alloy achieves low melting points, improved durability, crack resistance, and erosion resistance, while effectively suppressing void formation, thereby enhancing the reliability and performance of electronic circuit boards.
Implementation Method 1
the melting point can be suppressed to a low level
Data Source
Figure 1
AI summary
A solder alloy is a tin-silver-copper solder alloy, and contains tin, silver, copper, bismuth, nickel, and cobalt. Relative to the total amount of the solder alloy, the silver content is 2 mass% or more and 4 mass% or less, the nickel content is 0.01 mass% or more and 0.15 mass% or less, and the cobalt content is 0.001 mass% or more and 0.008 mass% or less.