Solder Alloy Composition for Suppressing Liftoff Phenomenon
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Solution Overview
Problem
Existing solder alloys face issues with fillet abnormalities such as liftoff phenomenon, solder bridges, and solder icicles during flow soldering, which are not adequately addressed by specifying only the liquidus and solidus temperatures, and are influenced by the segregation of Bi and other elements during solidification.
Innovation Solution
A solder alloy composition with Bi content between 0.1% and 0.8%, Ag between 0% and 0.3%, Cu between 0% and 0.7%, and P between 0.001% and 0.1%, with specific solid and liquid phase ratios at 235°C and 210°C, respectively, is developed to suppress the occurrence of liftoff phenomenon and enhance thermal fatigue resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If Bi content is increased to improve thermal fatigue resistance, then thermal fatigue resistance is improved, but liftoff phenomenon occurs more frequently
Solution Approach 1:
The patent optimizes the Bi content parameter to a specific range (0.1-0.8 mass%) rather than using high amounts, and combines it with controlled Ag content (0-0.3 mass%) to achieve the desired balance between thermal fatigue resistance and suppression of liftoff phenomenon
Solution Approach 2:
The patent creates a composite solder alloy system combining Bi, Ag, Cu, and P elements with specific compositional ranges, where the synergistic interaction between these elements achieves both improved thermal fatigue resistance and suppression of liftoff phenomenon that cannot be achieved by single element addition
2Reliability
If Ag and Bi content are increased to enhance thermal fatigue resistance, then thermal fatigue resistance is improved, but liquid phase ratio increases causing liftoff phenomenon
Solution Approach 1:
The patent establishes specific parameter ranges for Ag (0-0.3 mass%) and Bi (0.1-0.8 mass%) content, and defines target liquid phase ratio ranges at specific temperatures to control solidification behavior and prevent excessive liquid phase formation that causes liftoff
3Strength
If Cu content is increased to improve strength, then strength is improved, but solid phase ratio increases causing solder bridges and solder icicles
Solution Approach 1:
The patent optimizes Cu content to a specific range (0-0.7 mass%) and establishes target solid phase ratio ranges at specific temperatures to control solidification timing and prevent premature solidification that causes solder bridges and icicles while maintaining adequate strength
4Manufacturing precision
If P content is increased to improve wettability, then wettability is improved, but manufacturing precision requirements increase
Solution Approach 1:
The patent sets P content within a specific range (0.001-0.1 mass%) to achieve improved wettability while avoiding excessive P addition that would require stricter manufacturing process control, representing an optimization between performance and manufacturability
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 proposed solder alloy effectively suppresses the generation of liftoff phenomenon, solder bridges, and solder icicles, while providing enhanced thermal fatigue resistance, ensuring reliable connections in electronic components.
Implementation Method 1
a solid phase ratio at 235°C of 0.02 vol. % or less, and a liquid phase ratio at 210°C of 5.0 vol. % or less
Data Source
AI summary
A solder alloy has an alloy composition consisting of, in mass %: Bi: 0.1 to 0.8%; Ag: 0 to 0.3%; Cu: 0 to 0.7%; P: 0.001 to 0.1%, with the balance being Sn. A total amount of Ag and Bi is from 0.3 to 0.8% in the alloy composition.