Sn-Ag-Cu Solder Alloy with Ca or Mn Additives
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Solution Overview
Problem
Sn—Ag—Cu based solder alloys experience increased melting points when Ag content is reduced, leading to potential strength and reliability issues due to Bi deposition on joining interfaces, and existing compositions fail to optimize mechanical characteristics and reliability.
Innovation Solution
A solder alloy composition containing 2.0 to 4.0 wt% Ag, 0.5 to 1.0 wt% Cu, and 0.1 to 0.5 wt% of additive elements such as Ca or Mn, which improves strength, elongation, and reliability by preventing additive element segregation and reducing the likelihood of crack formation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If Ag content is reduced to lower cost, then solder cost decreases, but melting point increases and strength deteriorates
Solution Approach 1:
The invention changes the compositional parameters by introducing Ca and Mn elements in specific amounts (0.01-1.0 wt% each) to the Sn-Ag-Cu solder system. This parameter modification allows the solder to maintain adequate strength at reduced Ag content (0.1-5.0 wt%) while controlling intermetallic compound formation and preventing Bi segregation, thus resolving the contradiction between cost reduction and strength maintenance
Solution Approach 2:
The invention creates a composite solder alloy system by combining Sn, Ag, Cu, Ca, and Mn elements. The Ca and Mn elements work synergistically to modify the microstructure and intermetallic compound distribution, enabling the composite material to achieve both cost-effectiveness through reduced Ag content and mechanical strength through controlled intermetallic formation
2Temperature
If Bi is added to reduce melting point, then melting point decreases, but fragile Bi deposits on interface and fatigue lifetime shortens
Solution Approach 1:
The invention extracts Bi from the solder composition entirely, creating a Bi-free solder alloy. By removing the harmful Bi element that causes interface degradation and shortens fatigue lifetime, the invention eliminates the trade-off between melting point reduction and reliability, allowing the use of alternative elements like Ca and Mn that do not cause interface segregation
Solution Approach 2:
The Ca and Mn elements act as intermediary substances that modify the intermetallic compound formation behavior. These intermediaries control the growth and distribution of intermetallic compounds at the interface, preventing the direct harmful interaction between solder and electrode that would otherwise require Bi to mediate the melting point reduction
3Strength
If Sb is added to improve mechanical characteristics, then strength improves, but elongation deteriorates
Solution Approach 1:
The invention changes the alloying strategy by replacing Sb with Ca and Mn elements. This parameter substitution modifies the intermetallic compound type and distribution, achieving strength improvement through controlled intermetallic formation while maintaining elongation by avoiding the harmful effects of Sb-induced brittleness
Data Source
AI summary
In order to improve the strength and elongation of a solder and improve the reliability of a joining portion joined by the solder, the present invention provides a solder alloy that comprises 2.0 to 4.0 mass % of Ag, 0.5 to 1.0 mass % of Cu, 0.1 to 0.5 mass % of an additive element selected from the group consisting of Ca and Mn, and a balance of Sn.