Lead-Free Solder Alloy Composition for Shear Strength and Fusion Control
Find Innovative SolutionsGenerate Solutions
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 requiring high integration and high functionality, such as QFP and BGA, while also being antimony-free to comply with environmental regulations.
Innovation Solution
A lead-free and antimony-free solder alloy composition comprising 0.1 to 4.5% Ag, 0.20 to 0.85% Cu, 0.2 to 5.00% Bi, 0.005 to 0.09% Ni, and 0.0005 to 0.0090% Ge, with specific mass ratios and relations to optimize grain minuteness and balance of elements to enhance shear strength and prevent fusion failure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If conventional Sn-Ag-Cu solder alloy is used, then basic soldering function is achieved, but shear strength is insufficient and fusion failure occurs
Solution Approach 1:
The invention changes the chemical composition parameters of the solder alloy by adding specific amounts of Bi (0.1-5.0 mass%), Ni (0.01-0.1 mass%), and Ge (0.001-0.01 mass%) to the conventional Sn-Ag-Cu base composition. This parameter modification optimizes the microstructure and intermetallic compound formation, thereby improving both shear strength and preventing fusion failure simultaneously.
Solution Approach 2:
The invention creates a composite solder alloy system by combining multiple elements (Sn, Ag, Cu, Bi, Ni, Ge) in specific proportions. The synergistic interaction between these elements produces a composite material with enhanced mechanical properties and improved bonding reliability, where Bi refines grain structure, Ni controls intermetallic formation, and Ge prevents oxide formation.
2Strength
If Ni layer is added to back metal to improve wettability, then adhesive strength improves, but Ni leaching occurs when Ni layer melts into molten solder
Solution Approach 1:
The invention introduces Ge as an intermediary element that preferentially reacts with oxygen to form a protective oxide layer on the solder surface. This intermediary mechanism prevents direct contact between molten solder and Ni in the back metal, thereby suppressing Ni leaching while maintaining good wettability through the flux-assisted bonding process.
Solution Approach 2:
The invention modifies the solder alloy composition by adding Ni (0.01-0.1 mass%) and Ge (0.001-0.01 mass%) to control the chemical reactions at the interface. The specific parameter ranges are optimized to balance Ni's beneficial effect on wettability against its harmful leaching tendency, with Ge serving to mitigate the leaching through oxide formation.
3Object-generated harmful factors
If Ti barrier layer is formed to suppress Ni diffusion, then Ni diffusion is suppressed, but wettability deteriorates when Ti layer is exposed
Solution Approach 1:
The invention adjusts the solder alloy composition parameters, particularly adding Bi (0.1-5.0 mass%) and Ni (0.01-0.1 mass%), to optimize the wetting behavior on Ti surfaces. The specific composition ranges are designed to overcome Ti's poor wettability while maintaining its barrier function, enabling successful bonding even when Ti is exposed.
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 optimized solder alloy composition effectively suppresses fusion failure and improves shear strength, ensuring reliable bonding in high-integration electronic devices, while being environmentally friendly by avoiding lead and antimony.
Implementation Method 1
a barrier layer such as Ti is usually formed on the back metal to suppress Ni from diffusing into the silicon chip
Implementation Method 2
the molten solder wets the microelectrode, so that solder bumps are formed on the microelectrodes
Data Source
AI summary
Provided are a lead-free and antimony-free solder alloy, a solder ball, and a solder joint that 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 having an alloy composition consisting of, by mass %, 0.1 to 4.5% of Ag, 0.20 to 0.85% of Cu, 0.2 to 5.00% of Bi, 0.005 to 0.09% 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): 0.013≤(Ag+Cu+Ni+Bi)×Ge≤0.027 (1), Sn×Cu×Ni≤5.0 (2). Ag, Cu, Ni, Bi, Ge, and Sn in the relations (1) and (2) each represent the contents (mass %) in the alloy composition.