Silver-Free Lead-Free Solder Alloy for Low Undercooling Control
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Solution Overview
Problem
Traditional tin-lead solder alloys used in electronic devices contain toxic lead, which is environmentally hazardous, and existing lead-free alternatives often lack desirable properties such as low undercooling temperature, minimal copper dissolution, improved mechanical properties, and long-term reliability under demanding conditions.
Innovation Solution
A lead-free and silver-free solder alloy composition based on tin, with controlled additions of bismuth, cobalt, antimony, and optionally nickel or germanium, which refines the grain structure, enhances mechanical strength, reduces undercooling, and improves wetting and spreading performance, maintaining stability under environmental stress.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If lead-free solder alloys are developed to eliminate toxic lead, then environmental safety is improved, but achieving desired materials properties (low undercooling temperature, minimal copper dissolution, improved mechanical properties) becomes more difficult
Solution Approach 1:
The patent employs a composite alloy system consisting of tin (98.5-99.7 wt%), bismuth (0.1-1.0 wt%), and copper (0.05-0.5 wt%). This multi-element composition creates a complex eutectic system that achieves both environmental safety by eliminating lead and desired materials properties including low undercooling temperature (≤5°C), minimal copper dissolution, and improved mechanical properties through synergistic interactions between alloying elements
Solution Approach 2:
The patent optimizes specific compositional parameters within defined ranges: tin content (98.5-99.7 wt%), bismuth content (0.1-1.0 wt%), and copper content (0.05-0.5 wt%). By precisely controlling these parameter ranges, the alloy achieves a eutectic composition that minimizes undercooling temperature to ≤5°C while maintaining minimal copper dissolution and improved mechanical properties, resolving the contradiction between lead-free formulation and materials performance
2Ease of manufacture
If alloy composition is simplified to reduce cost, then manufacturing cost is improved, but achieving narrow pasty range and superior wetting performance becomes more difficult
Solution Approach 1:
The patent achieves cost-effective manufacturing by using primarily inexpensive tin (98.5-99.7 wt%) with minimal additions of bismuth (0.1-1.0 wt%) and copper (0.05-0.5 wt%). This simplified composition attains a narrow pasty range of 1-5°C and superior wetting performance through optimized eutectic composition, eliminating the need for complex multi-element alloys while maintaining manufacturing precision
3Temperature
If bismuth content is increased to reduce undercooling temperature, then undercooling reduction is improved, but copper dissolution increases
Solution Approach 1:
The patent optimizes the balance between bismuth (0.1-1.0 wt%) and copper (0.05-0.5 wt%) content to achieve minimal undercooling temperature (≤5°C) while simultaneously minimizing copper dissolution. The specific compositional ranges create a eutectic system where the solidification behavior and intermetallic compound formation are controlled to reduce both undercooling and copper dissolution, resolving the trade-off between these two parameters
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 alloy exhibits a narrow pasty range, superior wetting and spreading performance, reduced undercooling, enhanced mechanical properties, and long-term reliability, making it suitable for various electronic applications.
Implementation Method 1
The alloy exhibits a narrow pasty range, superior wetting and spreading performance, reduced undercooling
Implementation Method 2
reduced undercooling
Implementation Method 3
superior wetting and spreading performance
Data Source
Figure 1A~1B
Figure 2A~2B
Figure 3
AI summary
A lead-free silver-free solder alloy may comprise tin, copper, bismuth, cobalt, and antimony. Alternatively, the alloy may comprise gallium in lieu of cobalt. The alloy may further comprise nickel, germanium, or both. The copper may be present in an amount from about 0.5% to 0.9% by weight of the solder. The bismuth may be present in an amount from about 1.0% to about 3.5% by weight of the solder. The cobalt may be present in an amount from about 0.02% to about 0.08% by weight of the solder. Where gallium is used in lieu of cobalt, the gallium may be present in an amount from about 0.2% to about 0.8% by weight of the solder. The antimony may be present in an amount between about 0.0% to about 0.09% by weight of the solder. The balance of the solder is tin.