Lead-Free Solder Alloy Composition With Reduced Undercooling
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Solution Overview
Problem
Existing lead-based solder alloys used in electronic applications are toxic and environmentally hazardous, necessitating the development of lead-free alternatives with improved mechanical and thermal properties for extreme environments.
Innovation Solution
A lead-free solder alloy composition comprising 3.8 wt.% silver, 0.7 wt.% copper, 1.5 wt.% bismuth, 0.05 wt.% cobalt, 0.008 wt.% titanium, and balance tin, optionally with nickel, which enhances mechanical strength, reduces undercooling temperature, and provides high temperature creep resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If lead-free solder alloys are developed to replace toxic tin-lead based alloys, then environmental safety is improved, but mechanical strength and reliability deteriorate
Solution Approach 1:
The patent employs composite material design by combining multiple elements (Sn-3.8Ag-0.7Cu-1.5Bi-0.05Co-0.008Ti) to create a lead-free solder alloy that achieves both environmental safety and superior thermo-mechanical reliability. The synergistic interaction between different elements produces a composite material with properties exceeding those of individual components, particularly in high-temperature creep resistance and mechanical strength.
Solution Approach 2:
The patent applies parameter changes by precisely controlling the composition ratios of each element in the solder alloy. By optimizing the weight percentages of silver (3.8%), copper (0.7%), bismuth (1.5%), cobalt (0.05%), and titanium (0.008%), the alloy achieves a balance between environmental compatibility and enhanced mechanical properties, including reduced undercooling temperature and improved reliability in extreme environments.
2Strength
If traditional tin-lead based alloys are used to achieve desired materials properties, then mechanical properties are improved, but environmental hazards worsen
Solution Approach 1:
The patent extracts and eliminates the harmful lead component from traditional solder alloys while retaining and optimizing the beneficial elements (silver, copper, and adding bismuth, cobalt, and titanium). This extraction of the toxic substance allows the development of an environmentally safe alloy that maintains or improves mechanical properties through the synergistic combination of remaining and added elements.
Solution Approach 2:
The patent changes the compositional parameters by removing lead and precisely controlling the percentages of other elements. This parameter optimization enables the lead-free alloy to achieve desired mechanical strength and reliability without the environmental hazards associated with lead-containing materials.
3Reliability
If lead-free solder alloys are designed for extreme environments, then high temperature creep resistance is improved, but undercooling temperature increases
Solution Approach 1:
The patent applies parameter changes by optimizing the composition ratios of elements to achieve a balance between high-temperature creep resistance and undercooling characteristics. The specific formulation (Sn-3.8Ag-0.7Cu-1.5Bi-0.05Co-0.008Ti) creates a microstructure that provides both high-temperature stability and controlled solidification behavior, reducing undercooling while maintaining creep resistance.
Solution Approach 2:
The patent uses composite material design where the interaction between different elements creates a microstructure that simultaneously improves high-temperature creep resistance and reduces undercooling temperature. The combination of bismuth, cobalt, and titanium with silver and copper produces synergistic effects that address both thermal properties.
Data Source
Figure 1A~1B
Figure 2A~2B
Figure 3
AI summary
A lead-free solder alloy is based on tin and comprises silver, copper, bismuth, cobalt and titanium. The alloy may further comprise antimony, nickel, or both. Silver is present in an amount from 3.1% to 3.8% by weight of the solder. Copper is present in an amount from 0.5% to 0.8% by weight of the solder. Bismuth may be present in an amount from 0.0% (or 1.5%) to 3.2% by weight of the solder. Cobalt is present in an amount from 0.03% to about 1.0% (or 0.05%) by weight of the solder. Titanium is present in an amount from 0.005% to 0.02% by weight of the solder. Antimony may be present in an amount between 1.0% to 3.0% by weight of the solder. The balance of the solder is tin.