Lead-Free Solder Alloy Composition for Creep Resistance and Workability
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Solution Overview
Problem
Conventional solder alloys face challenges with creep resistance and workability, particularly in extreme temperature environments, and existing solutions fail to adequately address these issues while minimizing flux residue and processing defects like edge cracks.
Innovation Solution
A lead-free solder alloy composition consisting of Ag: 0 to 4%, Cu: 0.1 to 1.0%, Ni: 0.01 to 0.3%, Sb: 5.1 to 7.5%, Bi: 0.1 to 4.5%, Co: 0.001 to 0.3%, P: 0.001 to 0.2%, with the balance being Sn, optimized to satisfy specific relationships that enhance creep resistance, workability, and melting point, and can be used in preform or paste form for improved reliability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional Sn-3Ag-0.5 Cu solder alloy is used, then the joint may be broken under temperature variations, but improving creep resistance by adjusting composition degrades workability and causes edge cracks
Solution Approach 1:
The patent applies parameter changes by precisely adjusting the compositional parameters of the solder alloy. Specifically, it limits Ag to 0-4%, Cu to 0.1-1.0%, Ni to 0.01-0.3%, Sb to 5.1-7.5%, Bi to 0.1-4.5%, Co to 0.001-0.3%, and P to 0.001-0.2%. This compositional optimization resolves the contradiction by finding the optimal parameter range that provides sufficient creep resistance for joint reliability while preventing excessive brittleness that would cause edge cracks during processing.
Solution Approach 2:
The patent employs composite materials by creating a multi-element solder alloy system that combines Sn with carefully controlled amounts of Ag, Cu, Ni, Sb, Bi, Co, and P. This composite approach allows the alloy to achieve both improved creep resistance through the synergistic effects of multiple elements and adequate ductility for workability, resolving the technical contradiction between reliability and ease of manufacture.
2Ease of operation
If solder paste with flux is used, then soldering can be performed, but flux residue adheres to the soldered part causing corrosion and insulation resistance decrease
Solution Approach 1:
The patent applies the disposable principle by promoting the use of preform solder instead of solder paste with flux. The preform solder is a self-contained, disposable component that eliminates the need for flux entirely. This resolves the contradiction by providing a soldering solution that achieves the necessary soldering capability without generating any flux residue that could cause corrosion or insulation problems.
3Reliability
If solder alloy with high creep resistance is developed, then joint reliability improves, but edge cracks occur during rolling step
Solution Approach 1:
The patent resolves this contradiction through parameter changes by optimizing the compositional parameters within specific ranges. The controlled addition of elements like Ni (0.01-0.3%), Co (0.001-0.3%), and P (0.001-0.2%) along with Sb (5.1-7.5%) and Bi (0.1-4.5%) creates an alloy that achieves high creep resistance while maintaining adequate ductility to prevent edge cracks during the rolling manufacturing process.
Solution Approach 2:
The patent uses composite materials by formulating a complex multi-element alloy system where each component contributes specific properties. The combination of Sn base metal with controlled amounts of Ag, Cu, Ni, Sb, Bi, Co, and P creates a composite material structure that simultaneously provides creep resistance for reliability and sufficient workability to prevent manufacturing defects like edge cracks.
Data Source
AI summary
A solder alloy has an alloy composition consisting of, in mass %, Ag: 0 to 4%, Cu: 0.1 to 1.0%, Ni: 0.01 to 0.3%, Sb: 5.1 to 7.5%, Bi: 0.1 to 4.5%, Co: 0.001 to 0.3%, P: 0.001 to 0.2%, and the balance being Sn.