Lead-Free Solder Alloy High-Temperature Strength
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Solution Overview
Problem
Existing lead-free solder alloys face challenges in maintaining bonding strength at high temperatures over long periods and lack versatility in application, requiring higher soldering temperatures and limited composition ranges.
Innovation Solution
A lead-free solder alloy composition with Sn-Cu-Ni as the base, including specific amounts of Bi, Ge, and unavoidable impurities, which suppresses bonding strength degradation even at high temperatures, offering high reliability and versatility.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If Bi is added to increase mechanical strength and decrease solidus temperature, then joining strength is improved, but soldering temperature control becomes more complex and reliability at high temperature deteriorates
Solution Approach 1:
The patent optimizes the Bi content parameter within a specific range (0.01-5 wt%) to balance joining strength and high-temperature reliability. This parameter change resolves the contradiction by finding the optimal concentration that provides sufficient mechanical strength while preventing excessive Bi accumulation that would cause reliability deterioration at high temperatures.
Solution Approach 2:
The patent creates a composite solder alloy system combining Sn, Cu, Ni, and Bi elements. This composite material approach resolves the contradiction by synergistically combining the strength-enhancing effect of Bi with the high-temperature stability provided by Sn-Cu-Ni base alloy, achieving both improved joining strength and maintained reliability.
2Strength
If Cu and Ni are added to form intermetallic compounds for strong joining, then joining strength is improved, but soldering temperature increases significantly
Solution Approach 1:
The patent optimizes Cu content (0.1-3 wt%) and Ni content (0.01-0.5 wt%) parameters to control intermetallic compound formation. By precisely controlling these parameter ranges, the patent achieves strong joining through intermetallic compounds while limiting the soldering temperature increase to a manageable level, resolving the contradiction between strength and temperature.
3Temperature
If Sb is added in large amounts to decrease solidus temperature, then melting point is reduced, but solidus temperature remains high and soldering process complexity increases
Solution Approach 1:
The patent replaces large amounts of Sb with optimized Bi content (0.01-5 wt%) and adjusts the Sn-Cu-Ni base composition. This parameter change achieves effective solidus temperature reduction without requiring complex soldering processes, as Bi provides better melting point control and wettability compared to high Sb content alloys.
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AI summary
Provided is a lead-free solder alloy and soldering capable of maintaining strong joining strength even in a high-temperature state after soldering and having high reliability and versatility. The lead-free solder alloy composition of the present invention has Sn-Cu-Ni as a basic composition, which includes 0.1 to 2.0 mass% of Cu, and 0.01 to 0.5 mass% of Ni, 0.1 to 5 mass% of Bi, and 76.0 to 99.5 mass% of Sn, such that it is possible to implement soldering with high reliability without decreasing joining strength of a soldered joint even in a state of being exposed to high temperature for a long time, as well as joining strength at the time of bonding.