Lead-Free Solder Alloy Composition for Stronger, Fusion-Stable Joints
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Solution Overview
Problem
Existing lead-free Sn—Ag—Cu solder alloys face challenges in achieving improved shear strength, suppressing fusion failure, and addressing Ni leaching, particularly in applications like BGA and QFP, while also being antimony-free to comply with environmental regulations.
Innovation Solution
A lead-free and antimony-free solder alloy composition with specific balances of Ag, Cu, Ni, and Ge contents, along with optional elements, to enhance shear strength and prevent fusion failure by optimizing intermetallic compound formation and oxide film suppression.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If Sn-Ag-Cu solder alloy is used to improve wettability and basic bonding, then solderability is improved, but shear strength is insufficient and fusion failure occurs
Solution Approach 1:
The patent uses a composite solder alloy system combining Sn-Ag-Cu base elements with additional Ni and Ge elements. This composite composition creates multiple intermetallic compounds (Cu6Sn5, Cu3Sn, Ni3Sn4, NiSn) that work synergistically to provide both good wettability from the Sn-Ag-Cu base and enhanced shear strength from the Ni and Ge additions, resolving the contradiction between solderability and strength
Solution Approach 2:
The patent optimizes the concentration parameters of each element within specific ranges: Ag (2.0-4.0%), Cu (0.5-1.0%), Ni (0.01-0.1%), and Ge (0.003-0.008%). By precisely controlling these compositional parameters, the alloy achieves optimal balance between wettability (provided by Sn-Ag-Cu) and shear strength (enhanced by Ni and Ge intermetallic compounds), preventing both fusion failure and excessive strength
2Reliability
If Ni layer is added to improve heat cycle resistance, then heat cycle resistance is improved, but Ni leaching occurs and adhesive strength is reduced
Solution Approach 1:
The patent introduces Ge as an intermediary element that forms NiGe and Ni3Ge intermetallic compounds. These Ge-containing compounds act as barrier phases that suppress Ni leaching into the solder matrix while maintaining heat cycle resistance. The Ge elements mediate between the Ni layer and the solder, preventing direct Ni-Sn diffusion that would cause leaching and adhesive strength reduction
Solution Approach 2:
The patent creates a composite intermetallic compound system including Ni3Sn4, NiSn, NiGe, and Ni3Ge phases. This composite structure provides heat cycle resistance through the Ni-based compounds while the Ge-containing compounds (NiGe, Ni3Ge) form a protective barrier that prevents Ni leaching, thus maintaining both heat cycle resistance and adhesive strength
3Strength
If Ge content is increased to improve impact resistance and discoloration resistance, then impact resistance is improved, but alloy composition balance is disrupted
Solution Approach 1:
The patent optimizes Ge content within a narrow range (0.003-0.008%) to achieve impact resistance and discoloration resistance while maintaining alloy balance. This precise parameter control ensures Ge provides sufficient strengthening effect without excessive oxide formation or liquidus temperature increase that would disrupt composition stability
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 alloy composition achieves improved shear strength, suppresses fusion failure, and inhibits Ni leaching, ensuring reliable bonding in electronic devices with reduced environmental impact.
Implementation Method 1
Ni atoms diffuse into the molten solder and Ti hardly diffuses into the Ni
Implementation Method 2
the solder balls are melted by heating in a reflow furnace, and the molten solder wets the microelectrode, so that solder bumps are formed
Implementation Method 3
oxide film suppression
Implementation Method 4
the molten solder wets the microelectrode
Data Source
AI summary
Provided are a lead-free and antimony-free solder alloy, a solder ball, and a solder joint, which have improved shear strength obtained by grain minuteness at a bonded interface and can suppress fusion failure. The lead-free and antimony-free solder alloy has an alloy composition consisting of, by mass %, 0.1 to 4.5% of Ag, 0.20 to 0.85% of Cu, 0.005 to 0.090% of Ni, and 0.0005 to 0.0090% of Ge with the balance being Sn, and the alloy composition satisfies the following relations (1) and (2): 0.006≤(Ag+Cu+Ni)×Ge<0.023 (1), (Sn/Cu)×(Ni×Ge)/(Ni+Ge)<0.89 (2). Ag, Cu, Ni, Ge, and Sn in the relations (1) and (2) each represent the contents (mass %) in the alloy composition.